Phytogeny, evolution and classification of the Branchiopoda (Crustacea)

Transcription

1 l - I y d w b U M w 412: , i m (f) 1999 K hm er Academie Publisher.';. Printed in the Netherlands. 191 Phytogeny, evolution and classification of the Branchiopoda (Crustacea) Stefan Negrea1, Nicolae Botnariuc2 & Henri J, Dumont3* 1Institute oj'speoiogy 1Emile Rucoviiza \ Romanian A cadem y o f Sciences, Frumocisa 11, BucurestL Rom ania 2Biological Faculty, University o f Bucharest, SpL Independentei 93-95, Bitcuresti, Rom ania *Institute o f Anim al Ecology, University o f Ghent, Ledeganckstraat, 35, 9000 Gent, B elgium R eceived 2 0 July in revised form 5 July 1999; accepted 14 July 1999 Key words: Branchiopoda, paleontology, phylogeny, evolution, classification A bstract We present a cladistic analysis of all branehiopod groups, using a total of 42 morphological characters. The class Branchiopoda is composed of live superorders and 11 orders (nine recent, two fossil). The orders Ctenopoda, Anomopoda and Onychopoda form a monophyletie group, combined in the superorder Cladocera. The order Haplopoda, the fourth so-called cladoceran order (.v. tai. ), belongs to a new monotypie superorder, the Leptodorida, The cireumtropieal Cyciesteria hislopi is the sole representative of a new eonehoslraean order, the Cyclestherida. Abbreviations: As - Anostraca (outgroup); No - Notostraca; La - Laevicaudata; Sp - Spinicaudata; C'y - Cyclestherida; Ila - Haplopoda; Ct - Ctenopoda; Ap - Anomopoda; On - Onychopoda; Sd - presumed significance of the derived stales 14. Introduction In spite of exciting recent developments (see further), there is still uncertainly regarding the phylogenetic relationship and composition of the crustacean class Branchiopoda. In the present article, wc propose several modifications to the classification of the Branchiopoda, based on a cladistic analysis of three types of characters; anatomical, morpho-ecological (features which, like limbs and a carapace, became subject to modification by adaptation to specific food regimes) and ontogenetic (post-embryonic development, with or without larval stages). The results are presented as a cladogram (Figure 2) and as a phylogenetic tree (Figure 3). We conclude with a proposal for a phylogenetic classification and a characterisation of the live proposed super-orders. P resent state o f branehiopod classification A thorough analysis of former classifications of the Branchiopoda was made by Fryer ( 1987a), who pro * A u th o r lo r co[ti*spoikkik'c posed a new scheme. His analysis included classifications developed by Sars (1867, 1890), Gerstaecker ( ), Caiman (1909), Scourliekl (1926), Friksson (1934), Linder (1945), Preuss (1951 ), Brooks (1959), Tascli ( 1969), Flossner ( 1972) and Schram (1986). Fryer (loe. eil.) only overlooked one system, devised by Starobogalov (1986), in the same year as Schram's, and which published in Russian and, therefore, not widely available - is quite different in content and terminology from those of West Huropean and North-Ameriean authors. To complete the review by Fryer (1987a), we here present the classification of.starobogalov ( 1986), which lias been little used outside the Russianspeaking world (see Korovehinsky, 1990), Class Branehiopodiodes Caiman, 1909 I.Subclass Polyphemiones nov infraelass Speleoneclioni nom. nov. (= Remipedia Yaeger, 1981) Superorder Speleonectifbrmii I,L L L OrderSpeleoneeliformes, new status L 1.2, Superorder Tesnusoearid i fomii i

2 Order Tesnusocaridiformes nom. nov.(= Enantiopoda Birstein, 1960) 1.2. Infraclass Hutchinsonellioni nom. nov.(= Cephalocarida Sanders, 1955) Order Hutchinsonellifonnes nom. nov. (= Brachypoda Birstein, 1960) 1.3. Infraclass Polyphemioni nov, L3.1. Superorder Lepidocaridiformii Order Lepidocaridiformes nom. nov. (= Lipostraca Scourfield, 1926) Superorder Polyphemiformii Order Polyphemiformes nom. nov. (= Onychopoda Sars, 1865) Order Leptodoriformes nom. nov. (= Haplopoda Sars, 1865) 2. Subclass Branchipodiones Caiman, Infraclass Triopioni nom. nov. (= Calmanostraca Tasch, 1969) Superorder Odariiformii Order Odariiformes Simonetta & Della Cave, Superorder Triopiformii Order Triopiformes nom. nov. (= Notostraca Sars, 1867) Superorder Ketmeniiformii Order Ketmeniiformes nom. nov. (= Kazacharthra Novojilov, 1957) 2.2. Infraclass Branchipodioni Caiman, Superorder Leanchoiliformii Order Leanchoiliformes Stoermer, Order Yohiiformes Simonetta & Della Cave, Superorder Branchipodiformii Order Bracnhipodiformes nom. nov. (= Branchiopoda Latreille, 1917, =AnostracaSars, 1867) 3. Subclass Daphniiones nov Superorder Daphniifonnii Order Protocaridiformes Simonetta & Della Cave, Order Daphniiformes Milne-Edwards, 1840 (= Ctenopoda et Anomopoda Sars, 1865) Superorder Limnadiiformii (= Conchostraca Sars, 1867) Order Lynceifonnes nom, nov. (= Laevicaudata Linder, 1945) Order Limnadiiformes nom. nov, (j= Spinicaudata Linder, 1945) Starobogatovi system is not limited to the Branchiopoda, but includes all Crustacea. He divides "the superclass Crustacea into four classes (instead of 10-12) and nine subclasses, based upon the proportion between the prototagmata (i.e. the anterior and posterior groups of larval somites and the group of post- larval ones), and the definitive tagmata of the body, and on the general segmental structure of the body, as well as on the carapace form and the degree of het- eronomy of the trunk appendages". However, in using only those characters, his classification of the Branchiopoda is unacceptable. For example, it includes into the Branchiopoda certain groups of arthropods that do not belong there, viz.: 1. Remipedia ( Speleonectioni1); these are not bran chiopods (Fryer, 1987 a) 2. Cephalocarida ( Hutchinsonellioni1): generally considered to be non-branchiopoda (Fryer, 1987a) 3. Odoraici ( Odariiformes ): this largest of the bi- valved arthropods of the Burgess shales is not a branehiopod (Gould, 1989) 4. Leanchoilici ( Leanchoiliformes ) and Yohoia ( Yo- hoiiformes ): (Gould, 1989). these are not even crustaceans The- system of Schram (1986) was qualified by Fryer (1987a) as follows: this...classification of the Branchiopoda...suffers from several fundamental weaknesses... although based on computer programmes. The system is as follows: Class P hyllopoda I.Subclass Phyllocarida five orders, four of them extinct) 2. Subclass Cephalocarida 2.1. Order Brachypoda 2.2. Order Lipostraca 3. Subclass Sarsostraca 3.1. Order Anostraca 4. Subclass Calmanostraca 4.1. Order Notostraca 4.2. Order Kazacharthra 4.3. Order Conchostraca Suborder Laevicaudata 4.3.2, Suborder Spinicaudata 4.4. Order Cladocera Suborder Haplopoda Suborder Eucladocera Superfamily Sidoidea Superfamily Daphnoidea Superfamily Polyphemoidea Like Starobogatov, Schram included all Crustacea in his system. He divided the group into four

3 193 classes: the Remipedia, Malacostraca, Phyllopoda and Maxillopoda. The term branehiopod was abandoned as a taxonomie unit, and the Phyllopoda include two groups generally regarded as non-branchiopods, the Phyllocarida and the Cephalocarida. The conclusion reached by Fryer (1987a) was: whatever approach is used, requires reliable data for assessment. No computer programme can generate a meaningful system from inadequate elata and the system o f Schram reveals a lack of understanding of the animals involved, is based in part on erroneous or ambiguous data, and ignores biological reality. In our opinion, Fryer s (1987a) classification of the Branchiopoda is the best currently available, yet it still simplifies reality. It includes the following 10 orders: 1. Anostraca 2. Lipostraea+ 3. Spinicaudata 4. Laevicaudata 5. Ctenopoda 6. Anomopoda 7. Onychopoda 8. Haplopoda 9. Notostraca 10. KazachartlmH- (+ = fossii group). We accept these 10 orders which are well delimited. We do, however, doubt the conclusion that the Cladocera are "an unnatural group, an assemblage of organisms of diverse phyletic affinities and that the classification of branchiopoda is rendered difficult by the heterogeneous nature of the organisms involved. We here argue that branchipods are monophyietic and will present arguments to that effect in the following pages. Fryer s (1987a, b) position was first challenged by Walossek (1993), who used a phylogenetic analysis based on rather complex synapomorphies, concluded to branehiopod monophyly, listed characters on which to found the monophyietic units and formulated a ground pattern. Shortly thereafter, Martin & Cash-Clark (1993), stated: we disagree (with Fryer) that such trenchant differences among extant ciado- ecrans rentier useless any attempt to reconstruct the derivation of one group of cladocerans from another. Faced with the absence of a more likely evolutionary scenario, we postulate a phylogeny that assumes, instead, cladocerae monophyly. They return to the hypothesis of a derivation of the cladocerans from an ancestor of the cyclestheriids: we are attempting to clarify what Fryer (1987a) rightfully termed vaguely stated forms of the conchostracan-cladoceran theory. They conclude that their study had resolved a few morphological problems regarding onychopods, but recognize that several others await a solution before a more comprehensive attempt at a phylogeny of the cladoceran taxa becomes possible. Olesen (1996) and Olesen et al. (1997) recently tackled the phylogeny of the Conchostraca and Cladocera, giving great weight to the dorsal (neck) organ of the Conchostraca, the head-pores of the Cladocera and the structure of the male claspers in both. A recent study by Olesen (1998), based on 56 characters, subjects the Diplostraca (-Conchostraca and Cladocera) to a cladistic analysis. The results are interesting but challenging: certain forgotten higher taxa are reinstated (e.g. the Diplostraca and the Gymnomera = Onychopoda + Haplopoda). In line with cladist principles, a classificatory hierarchy without indication of absolute rank is suggested as well. The purpose of the present paper is slightly different: we aim at deriving a phylogenetic tree for all Branchiopoda, starting from the 10 order system of Fryer and at clarifying the phyletic relationship within Branchiopoda (excluding Onychina ) as established by Walossek (1993, 1995). Finally, we mention some attempts at deriving branehiopod phylogenies based on the base sequence of mitochondrial (12 S) genes (Hanner & Fugate, 1997; Schwenk et al., 1998). These papers produced only partial phylogenies but are very promising for the future. The ancestor o f th e Branchiopoda As usual, the fossil record is unsatisfactory. Some fossils, once considered as ancestral to the branchi o- pods, are the phyiiopod layer of the Burgess shales, dated to the middle Cambrian (c. 530 m y) (Walcott, 1912). This period of a rapid (not more than 5-10 M y) faunal diversification, known as the Cambrian explosion, is one of the first archives of multicellular animals with hard parts (Gould, 1989). Walcott s (1912) classification of Burgess shale branchiopoda is as follows: Order Anostraca: Opabinici, Leanchoilia, Yohoia, Bidentia Order Notostraca: N a n u m, ßurgessia, Anamcdocaris, Waptia.

4 194 These genera may, however, not even be crustaceans, except Naraoici, which is a highly specialized trilobite (Whittington, 1977; Gould, 1989). Others, like Opabinia and Anomalocaris, have been reassigned to totally new phyla. In 1976, Briggs described a new arthropod from the Burgess shales, Branchiocam n.gen.l a possible precursor of the branchi opods. It has a bivalved carapace that covers the head and anterior two thirds of the body. The body is composed of 46 segments and a bifid telson. The appendages appear to be biramous. The head is remarkable, devoid of any appendage behind the mouth. Briggs (loc. cit.) concludes: this organism seems to defy all classification within whatever group of recent arthropod. But Fryer (1987a) is of the opinion that..its appendages... indicate branehiopod affinities. Fryer (1987a) also mentions the discovery by Mikulic et al. (1985) of a silurian arthropod, as yet unnamed and which cannot with certainty be assigned to any major arthropod group, has... been suggested as showing possible branehiopod affinities. Likewise, Fryer (1987a) mentions that after Müller & Walossek (1985) such fossils and the excellently preserved minute Cambrian crustacean fauna from the Orsten of Sweden (...) suggest that the fossil record may yet provide evidence that will assist in tracing branehiopod history. Thus, Walossek & Muller (1990) and Budd (1996), dealing with the monophyietic origin of the Crustacea, discuss M artim so- nia from the Upper Cambrian Orsten formation of Sweden. According to Budd, Martinssonia possesses nearly all the characters associated with crown group crustaceans and is placed as the immediate sister taxon to them. For all these reasons, we assigned the ancestral branehiopod in our phylogenetic tree (Figure 3) to the Middle Cambrian. From this hypothetical ancestor are derived 1 monophyietic groups, which correspond to the ten terminal orders of Fryer (1987a) (Figures 1-3). A comment on the phylogenetic scheme of Walossek. In Walosseki conception (1993, 1995), the bran- chiopods are comprised of two phyletic lines: an anostracan and a phyiiopod line (Figures I and 3). In the Upper Cambrian, a distinctive lineage detached from that of the ancestral branehiopod (Figure 3). This supposition is based on the fossil Rehbachi- ella kinnekullensis from the Upper Cambrian Orsten (limestone modules) of Sweden (Muller, 1983). Walossek (1993, 1995) described the larval stages and discussed functional and comparative aspects of the fossil s morphology and ontogeny. He also proposed a phylogenetic scheme for the branchiopods, to fix the position of Rehbachiella as a member of the anostracan line (Figure 1). Walossek (pers. com.) added that I suggest that Rehbachiella should be at the base of the line leading to the tlipostraca and the recent anostraeans; since 1 call the whole monophylum based on autapomorphies the Anostraca, the recent group was suggested to be named the Eiumoslraca (see Figure 1), The characters for this are given in Walossek (1993), a major monograph on Rehbachi- ella, in which only the phylogeny of the Cladocera remained unresolved. Still in the Upper Cambrian, a second line detached from that of the ancestral branehiopod (Figure 3). Its principal apomorphy is compound eyes internalized and shifted dorsaly (Walossek, 1993, 1995). It gave rise to two derivations: the Cahnano.straca and the Onychura (Figure 1), The Calmanostraca presumably detached from the ancestor of the phyllopods during the Silurian since, according to Taseh ( 1969), Calmanostraca already existed in the Lower Devonian (Figure 3). Their basic apomorphies tue: a bottom mode of life with adjustment of the anterior trunk limbs for omnivorous feeding, a polymetamery of the trunk, and long multiannulate i'ureal rami. The ancestor of the Cainumoslruea evolved in two directions (Figure 3). One lineage lead to the order Notostraca, of which fossils are known since the Upper Carboniferous (Taseh, 1969; Fryer, 1987a; Walossek, 1993, 1995) and with a single family extant (Triop- idae). The second lineage gave way, in the Lower Jurassic (Lias) to several genera of the fossil family Ketmeniidae, classified among fkuxacharthra (Taseh, 1969). For further details on the phylogeny of the Calmanostraca, see Walossek ( 1993, 1995). The status of the second derivative of the phyl- lopod line, the Onycluira (sensu Walossek) remains unresolved. Here, we will only address the phyletic relationships of the conehoslracan- leptodorid-cladocerait line. According to Walossek (loc. cit), this line includes the Conchostraca (Spinicaudata and Laevicaudata) and Cladocera, with as basic apomorphy the presence of a bivalved secondary shield behind the larval head shield. He adds that their status within the Onychura is not well resolved (see

5 195 EUANOSTRACA (since Upper Jurassic) NOTOSTRACA (since Carboniferous) SPINICAUDATA (since Silurian) CLADOCERA (since Cretaceous) LAEVICAUDATA ( S in ce?) t LIPOSTRACA Lepidocaris (D evonian) K AZACHARTHRA (Triassic/Jurassic) CO NCHOSTRACA OSTRACA CALMA OSTRACA ONYCHURA t Rehbachiella (Upper Cam brian) Anterior trunk limbs modified for bottom life and omnivory, trunk polym clam cric, furcal ram i multiannulata (apom orphics for Calm anostraca BivaHcd carapace behiu 1 head shield (apo Inorphy for lychura) A N C E S T R A L S A R S O S T R A C A N Compound eyes internalized, shifted Compound eyes raised dorsnlly (apomorphy at front; naupliar nuchal for phyiiopod line organ reduced in early larval instars (apomorphy for anostracan line) LINE ANOSTRACAN PHYLLOPOD LINE M AXILLOPODA (Sin ce Upper Cam brian) Complex postmandibular filter-feeding apparatus with sternal food groove (apom orphy for branehiopod line) Osmoregulatory nuchal organ (apom orphy uniting Branchiopoda and M axillopoda) I. Presum ed phyletic relationship of the Branchiopoda according to Walossek (1995) (apomorphics arranged otherwise than in orgimtl). [ ' gure I, node seven). Walossek (1995) gives more details: Onychura develop a secondary shield behind the original head shield during ontogeny. It originates from tergal outgrowths of the maxillary of the lirst trunk somite and this structure is clearly not homologous to the large, bivalved head shields of other Crustacea, and is even unique among Arthropoda. However, one year later Fryer (1996) categorically slated that "there is no such thing as a secondary shield, a term that has been used instead of carapace in the Spinicaudata, Laevicaudata, Anomopoda, Ctenopoda, Haplopoda and Onychopoda. He concludes: "the concept of a secondary shield is erroneous and is based on a misunderstanding of the processes involved in carapace formation. To use the alleged possession of such a shield by all these orders as a synapo- morphy which unites them into one group, for which Walossek uses the outmoded name Onychura, is to base this unity on a non-existent character. Nor is the carapace of these orders always bivalved, nor do they all have a nauplius as claim ed...on a wider plane, there is no reason lo restrict the name carapace to cases

6 196 a n o - n o t o - l a e v e s p i n i - c y c l e s - h a p l o - S T R A C A S T R A C A C A U D A T A C A U D A T A T H E R ID A P O D A Since D ev onian Since C a rb o n i ferous Since C retaceous Since S ilu rian Since Perm ian Since Q u a te rn a ry C T E N O P O D A Since Q u atern ary ANOM O P O D A Since Perm ian O N Y C H O P O D A Since Q u a te rn a ry C a rap ac e encloses only tru n k ; lim bs t s a a i A n o m o p o d a ) 7 C L A D O C E R A N A N C E S T O R F irst p a ir o f tru n k lim bs in m ale w ith o u t clnspcr; m ctan au p liu s present (apom orphy for L eptodorid, line) 0 C a ra p a c e reduced to dorsal brood pouch; (ap o m o rp h ics for O nychopoda) O nly first p air of tru n k lim bs in male p erm an en tly w ith clasping hook; larv al stages absent (apom orphics for C ladocera» line) L E P T O D O R ID L IN E C a rap ace bivalved and w ith hinge; 16 p airs o f tru n k lim bs (apom orphics for Cyclestherida) CLADOCERAN L IN E C arap ace bivnlved, w ithout hinge; 4-6 pairs o f tru n k lim bs (apom orphics u n itin g C ladocera and L ep to d o rid» ) C Y C L E S T H E R IID Eyes n o t fused into a single organ; R eproduction gnm ogenctic w ith larval stages (apom orphy for Laevicaudata an d Spinicaudata) A N C E S T O R Both eyes fused to a single organ in nduits; tw o m odes of repro d u ctio n, b u t p red o m in an t mode is parthenogenesis w ith o u t larv al stages (apom orphics fo r C yclestherida plus L cptodorida and C ladocera) C O N C H O S T R A C A N C a ra p a c e d o rsal, univalvcd, covering h ead and a n te rio r portion of tru n k ; te rm in a l, long m ultiarticulatc furcal ram i (apom orphies for C alm anostrncan A N C E S T O R C a rap ace bivalved, en clo sin g tru n k an d head, o r only tru n k, or secondarily reduced to a dorsal brood pouch; a term in a l pair o f claw s, or a sim ple furca, som etim es secondarily ab sen t (apom orphies for C onchostraca» line) C A L M A N O S T R A C A C o m p o u n d eyes ex tern alized ; paired cau d al setae absent (ap o m o rp h ic s for A n o stra c a n line) 1 C O N C H O S T R A C A L IN E C om pound eyes internalized paired c audal setae presen t (apom orphics for Phyiiopod line) A N O S T R A C A L IN E P I I Y L L O P O D L IN E C om plex p ostm andibulnr filter-feeding a p p a ra tu s w ith stern al food groove (apom orphy fo r Branehiopod line) F ig u re 2, Cladogram of the presumed phyletic relationships of and within the Class Branchiopoda, with principal npomurplnes indicated.

7 197 PER IO D AND At least eleven (M ILLIO N S families Triopidne Leptodoridae Sididae Holopedidac Ten Familie*) Polyphemidae Podonidae Corcopagidae YEARS) ANOSTRACA NOTOSTRACA SPINICAUDATA HAPLOPODA LAEVICAUDATA CYCLESTHERIDA CTENOPODA ANOM OPODA ONYCHOPODA 1.8 T, F T, F F,S Moina O («Pi'iPP^Í Daphnia (ephippia) 136 è w /Asmusslltl c(t) f Esthcriell lae (T) t L I,enidae (T) t, Ipsilonll ae (T) T F,S Sim ocephalus (ephippia) * C Pro chydorus t 195,Vcrtexlidae (T) f t LIPOSTRACA 400 A N C'ESTRA t> A N C E STR ^ft^l'manostraca> ^ 435 SAUSOSTRACAN N. T, F a n c e s t r a l l e p t o d o r i d A N C E S T R A L C O N C H O S T R A C A N jj ANCESTRAL CLADOCERAN A N C E S T R A L B R A N C H Ï O P O D L E G E N D 2 O- 3 SARSOSTRACA 4 ANOSTRACA /-y,.[ re J, Iwolulionary live of the Branchiopoda constructed willi the help of data from the litemiure and from this arcticle. I. fossii or extant; 2, hypothetical; 3. Superorder (according to iliis article); 4. Order (according lo this article). F, from L;rycr ( 1087a); R» from Raymond (1946); S, from.smirnov ( ); T, from Taseh (I960); W, from Walossek (1993, 1995).

8 198 where all thoracic segments are fused to it (as in certain malaeostracans), as Walossek suggests. Carapace is a long-established and much used name that refers to a clearly defined, usually readily recognized structure whose nature and mode of origin are known; it should not be rejected, least of all on the basis of a misunderstanding'*. In spite of this rejected concept of a secondary shield, Walossek clearly has the merit to have demonstrated the phylogeny of the anostracan and phyllopod- calmanostracan lineages. We, therefore, reproduce his cladistic scheme (Figure 1), replacing the contested node seven by an alternative cladistic scheme (Figure 2), based on different apomorphies. The derivation of the conchostracan-leptodorid- cladoceran lineage from the ancestral phyiiopod probably took place in the Silurian (Walossek, 1995) or Lower Devonian (Taseh, 1969; Fryer, 1987a, see Figure 3). A reconstruction of the phylogeny of the B ranchiopoda Here, we attempt to identify phylogenetic Links of and within Branchiopoda, in the first place among the orders of the Onychura sensu Walossek, based on a cladistic analysis (Figure 2). M ethods Our phylogenetic hypothesis is based on an analysis of 42 characters (Table 1), using PHYLIP 3.5 (Felsenstein, 1989). Polymorphic characters of the initial matrix were converted to a binary state with the help of the FACTOR program. The resulting matrix was processed by a mixed parsimony algorithm (MIX, version 3.5c) using the WAGNER and CAMIN-SOKAL parsimony methods. The CAMIN-SOKAL method resulted in a single most parsimonious tree (tree length 131 steps) (Figure 2). The latter method was appropriate, since most characters were polarized series. Alternatively, PENNY (an algorithm for obtaining Dollo or polymorphism parsimony, version 3.5c) gave a clado- gram (TL 53) that was only marginally different in arrangement (therefore, not shown here). The WAG NER method produced two most parsimonious trees, but the consensus tree (not shown either) was again not substantially different from the tree obtained by both other methods. From the decomposition matrix cited above, we calculated a consistence and a FARRIS index, using PAUP (version and obtained the following summary statistics: tree length 110, consistency index and f (normalized) The cladograms obtained using PAUP and PHYLIP were so similar that we can assume that phylogenetic relationships were indeed obtained. Characters used in the phylogenetic analysis We indicate the plesiomorphic state by 0, and the derived states by 1, 2, 3, 4 or 5 (Table 1). The passage of polymorphic characters from one state to another was codified in the initial matrix. We selected the Anostraca as an outgroup. For selecting characters, we relied on Fryer (1987a), Botnariuc (1947, 1948), Negrea (1983), Rivier (1998), Thiéry (1996) and Walossek (1993, 1995). It should be added that characters 5-7, dealing with trunk limbs, are fairly general. Dumont & Silva-Briano (1997, 1998) opened up new possibilities (unfortunately limited to the Anomopoda) to use trunk limb morphology in sys- tematics and phylogeny, but these were not applied in our study. They may serve as a later, independent test (together with evidence derived from gene-sequences) of the phyletic system generated hereafter. Position and extension o f carapace 0 = absent (As); 1 = dorsally covering head and anterior portion of trunk (No); 2 = permanently enclosing trunk and head, no head shield (Sp, Cy); 3= permanently enclosing trunk only, head free, with head-shield (La, Ct, Ap); 4 = secondarily reduced to a dorsal brood pouch located at posterior extremity of Thorax (Ha); 5= secondarily reduced to a dorsal brood pouch located in the axis of the trunk (On). Sd: from a body without carapace to one that fully encloses the body, with or without a free head; secondarily reduced to a brood pouch in the predatory Haplopoda and Onychopoda. Structure o f carapace = absent (As); 1 = univalved ( head shield in Walosseki terminology) (No); 2= bivalved with a hinge (La, Sp, Cy); 3= bivalved without a hinge (Ha, Ct, Ap, On). Sd: from a carapace with a hinge to one without a hinge; the Notostraca are a case apart. Modification o f carapace infernale 0= absent (As); 1= not modified (No, La, Sp); 2 - more or less modified to brood pouch (in partheno- genetic female) or as an ephippium (in gamogenetic

9 Table I. A b b re via tio n s; As - Anostraca (out group); No - Notostraca; La - Laevicaudata; Sp - Spinicaudata; Cy - Cyclestherida; Ha - Haplopoda; C t - Ctenopoda; Ap - Anomopoda; On - Onychopoda; 0 - plesiomorphic; 12,3,4,5 - apomorphic (derived states 1,2,3,4,5) 199 No Character As No La Sp cy Ha Cl Ap On 1 Position and extension of carapace Structure of carapace Modification of carapace in female 0 1 I Shape of dorsal organ in adult ! Shape of telson (postabdomen) in female Shape of telson (postabdomen) in male Armature of telson (postabdomen) in both sexes Type of trunk limbs in female Number of trunk limbs in female IO Numbers of pairs of prehensile trunk limbs in male 11 Exopoditus of trunk limbs Osmoregulatory (branchial) epipodites in adult 13 Segmentation of trunk 0 0 t) Segments of trunk with appendages (} Paired caudal setae ( Number of rami of antennae Number of segments of antennae (per branch) 18 Muscles of antennae Number of segments of antennules in both sexes Position and number of sensillae of antennules in female 21 Position and number ofsensilllae of antennules in male I Shape of antennules in male Position of compound eyes in adult J 24 Number of compound eyes in adult I Type of mandible c mandibular muscles in adult Type of maxillules 0 1 Í) Type of maxillae Shape of food groove Structure of heart Ventral ganglia J 32 Shape of ovaries Position of ovaries Position of female genital opening Type of resting eggs I 0 36 Position of eggs (embryos) Development in ovisac/brood pouch ! I 38 Development from resting eggs I I 1 39 Nährboden ( placenta ) Opening of vasa dcferentia 0 t Penes Number and type oflarval stages

10 200 females of Anomopoda) (Cy, Ct, Ap). 3= secondarily reduced to a brood pouch with large ventral aperture (Ha); 4= secondarily reduced to a brood pouch, closed to the exterior (On). Sd: from a simple carapace to one with increasingly complex modifications aimed at protecting eggs, resting embryos (ephippia) and parthenogenetic juveniles. Shape o f nuchal organ in adults 0= more or less developed, circular or oval, as the rest of the dorsal organ of the larval stages (As,No,La,Sp,Cy). 1= well developed as an adhesive organ (Ct); 2 - less developed, sometimes rudimentary, circular or elongate (Macrothrix, Eurycercus) or even absent (Diaphanosoma, Acantholeberis, Bosmina) (Ap); 3= well developed into a nuchal plate (Ha, On). Sd: decrease in size and, rarely, change in function (Sida); developed into a nuchal plate in predators (Ha, On). For more information, see Olesen (1996). Shape o f telson (postabdomen) infernale 0= short and cylindrical (with terminal, flattened furcal rami in As; with terminal pair of multi-article rami in No); 1= more or less massive (with terminal pair of claws in Sp, Cy, Ct, Ap); 2 - feebly developed (without terminal furcal rami in La; terminating in a simple furca, sometimes secondarily absent, or in a long filament probably derived from fused furcae in On); 3= long and cylindrical, similar to abdominal1 segments (with simple furcae in Ha). Sd: from a short telson with furcal rami to a more or less developed postabdomen with terminal claws; secondarily reduced in predatory onychopods. Haplopods stands apart. Shape o f telson (postabdomen) in male 0= telson short, similar to female (As, No); 1= postabdomen weakly developed, similar to female (La); 2= postabdomen essentially a more or less massive prolongation (Sp, Cy, Ct); 3= postabdomen often markedly modified for copulation (exception: Euiycereus) (Ap); 4 = teslon long and cylindrical, similar to female (Ha); 5= presumed telson more or less short, as in female (On). Sd: from weakly to strongly developed; secondarily modified for copulation or reduced (in Onychopoda). Haplopoda stand apart. Armature o f telson (postabdomen) infernales and males 0= without setae, spinules or spines (As); 1= with few setae and spinules; spines only on posterior margin (No); 2= with few spinules only (La,Ha); 3= with more or less numerous setae, spinules and spines (even denticles) on dorso-lateral margin (Sp, Cy, Ct, Ap); 4 - secondanly without spines, but sometimes with line, short setae (On). Sd: from absence of an armature to a more and more complex one. Secondarily reduced in Onychopoda. Type o f trunk limbs in fem ales 0= foliaceous, fittratory (showing strong degree of serial homology, with small differences in shape and sizes in As; showing strong degree of serial homology but differing in size along a longitudinal gradient in La and Cy; quasi-similar in shape (but 6th pair reduced in Ct); 1= foliaceous but non-filtnuory (projecting laterally, differing in structure from all other orders in No); 2= foliaceous but extremely variable in shape, modified according to function (filtration, grasping, guiding particles in Ap); 3- stenopodous, cylindrical, segmented, differing in size and shape along longitudinal axis, reminescent of limbs of metanauplius or postmetanauplius (On); 4= stenopodous, cylindrical, segmented, grasping thoraic limbs quasi-similar in shape but differing in size, the first one by far the longest (Ha). Sd: from limbs that are almost similar to limbs that are progressively specialized according to their function (see Fryer, 1987a). Number o f trunk limbs in fem ales 0= 11 pairs, exceptionally 17 or 19 pairs (As); 1= pairs (No); 2= pairs, but exceptionally up lo 32 pairs in some species (La, Sp, Cy); 3= 5-6 pairs, exceptionally (Guernella, Neoihrix) the fifth pair rudimentary (Ha, Ct, Ap); 4= 4 pairs (On). Sd: reduction in the number of pairs of trunk limbs with phyiiopod lineage. Number o f pairs o f prehensile trunk limbs in males (used in mating) 0= no prehensile limbs (As, No); 1= first two pairs modified to stout claspers (Sp); 2= first pair modified to claspers, second pair either unmodified, or only slightly modified (Lynceus), or only left or right limb prehensile (Lynceopsis) (La); 3^ only first pair with clasping hook (Cy, Ct, Ap, On); 4= first pair without clasping hook but, occasionally, old males with a curved spine distally (Ha). Sd: except in the

11 201 Anostraca, where the (second) antennae are modi lied to prehensile organs, and the Notostraca, all other branchiopods have one or two pairs of trunk limbs modified to some extent. Exopodiies o f trunk limbs 0= present (As, No, La, Sp, Cy, Ct, Ap, On- except Cereopagidae where they are replaced by a small chitinized outgrowth); 1= absent (Ha). Sd: exopodites conserved in evolution, except in Leptodorida. O smo regid at m y (branchial) epipodites in adults 0= present on each limb (As, No, La, Sp, Cy); 1= present but reduced (Ct, Ap); 2= absent (Ha, On). Sd: reduction and loss in Haplopoda and Onychopoda (predators witli cylindrical legs). Segm entation o f trunk 0= usually all segments distinctly individualized (19-27 post-cephalic segments plus a telson in As; cylindrical 'segments' in No; up to 32 - at least! - trunk segments in Sp; 16 trunk segments in Cy; trunk segments in La); I only elongate abdomen clearly segmented (3 segments plus a telson); thoracic segmentation obscured by fusion (Ha); 2= mostly all segments obscured by fusion (Ct, Ap, On). Sd: from a distinct segmentation to a total fusion of all segments. Segm ents o f trunk bearing appendages 0= only anterior part of trunk ( thorax ) with appendages (As, No, Ha, Ct, Ap, On); I - anterior ( thorax ) and posterior { abdomen ) part of trunk with appendages (La, Sp, Cy). Sd: (in the phyiiopod lineage) reduction in the number of limbs and concentration thereof in the anterior zone (thorax) of the trunk; limb segments progressively fused (see also characters 9 and 12). Paired caudal setae ('abdom inalsetae', setae nata to res') ()~ absent (As); 1= small dorsal sensorial setae (No); 2= more or less developed (La, vsp, Cy, Ct, Ap); 3= secondarily reduced (rather small in On, but exceptionally developed in Polyphem us, though lost in adult of Cercopagis); 4= very small (Ha), Sd: from absence to more or less well developed caudal setae; secondarily reduced in predatory orders Haplopoda and Onychopoda, with complete loss in adult Cercopagis ( which have a compensatory long caudal appendage, see Negrea, 1983 and Rivier, 1998). Num ber o f antennal ram i 0= uniramous (As, No); 1= biramous (La, Sp, Cy, Ha, Ct -secondarily uniramous in female o i H olopedium -, Ap, On). Sd: from a uniramous to a biramous, natatory antenna. Num ber o f antennal segm ents (per branch) 0= Linsegmentcd (As, in No vestgial or absent); 1= multisegmented (up to 28 in La, up to 23 in Sp, up to 8 in Cy, 4 in Ha, 2-3 in Ct, 3-4 in Ap and On). Sd: from unsegmented to multisegmented. In the phyiiopod lineage, a reduction in the number and elongation of the segments occurs. Antennal m uscles Q= all extrinsic muscles on same side of body as the appendage served (As, No, Sp, Cy); 1=some extrinsic muscles originate on opposite side of body (Ha, La, Ct, Ap, On). Sd: situation 1 represents an evolutionary advance over situation o (see Fryer, 1987a; Olesen, 1998). Num ber o f segments o f antennules infernale and nude 0= one segment (As, No, Cy, Ha, Ct, Ap, On); 1= two segments (La,Sp). Sd: The antennules are uniramous and unsegmented, the Laevicaudata and Spinicaudata excepted. Position and num ber o fsen silla e on antennules in fem ales 0= confined to tip (several apical sensillae in As, No, Cy, Ha, Ct, Ap, On); 1= not confined to tip (numerous sensillae laterally on swollen distal segment in La; several lateral lobes with numerous sensillae on distal segment in Sp). Sd: a progressive concentration of sensillae at the tip of the antennules (except in Laevicaudata and Spinicaudata). Position and num ber o fsen silla e on antennules in male 0 - confined to tip (several apical or apical and subap- ical sensillae, with or without apical flagellum in As, No, Cy, Ap, On); 1= not confined to tip (numerous lateral sensillae on distal segment in La; several lateral lobes with numerous sensillae on distal segment in Sp; up to 70 lateral sensillae along the anterior margin in Ha; lateral tuft ofsensillae at the base of a long flagellum in Ct). Sd: like in the females, concentration of sensillae at the tip of the antennule, but males have an extra flagellum, or other structures for grasping females.

12 202 Shape o f antennules in the male 0= short and tubular, differing in length according to species, not modified for grasping females (As, No, On); 1= elongate (in La less than in Sp) and not modified for grasping females (La, Sp, Cy, Ha); 2= elongate and modified for grasping (Ct, but in Holopedium similar in both sexes); 3= often longer than in female, mostly only slightly modified for clasping in Macrothricids and Chydorids, frequently with grapling spine (Ap). Sd: from simple antennules to antennules modified for use in mating. Position o f compound eyes in adults 0= externalized, raised on front (As); 1= internal, usually located at antero-dorsal or frontal part of head (No, La, Sp, Cy, Ha, Ct, Ap and On- where they occupy most of the head cavity). Sd: from external, stalked eyes (As) to internal eyes, the largest being found in Onychopods. N um ber o f com pound eyes in adults 0= two unfused eyes (As, No, La, Sp); 1= two eyes fused to single organ (Cy, Ha, On and Ap). Secondarily reduced in M onospilus, Bryospilus, Nicsmirnovius and some A lona; lost in cave-inhabiting Alona). Sd: from two separated to one or no eye. Type o f mandible 0= grinding-rolling type (sometimes with secondary modifications for biting in As; La, Sp, Cy, Ct, Ap; adapted for biting in On); 1= biting type (massive, with biting molar region in No); 2= styliform type (not grinding in Ha, a unique type in branchiopods - see Fryer, 1987a). Sd: standard mandible of the grinding- rolling type, modified in predatory branchiopods into either a biting type (Onychopoda) or a special, unique type (Notostraca, Haplopoda). Type o f maxillae 0= reduced to small, simple lobes with or without setae (As, No where absent in some species of Triops, La, Sp, Cy, Ct); 1= reduced to a mound or apparently absent (Ap); 2= absent (Ha, On). Sd: reduction and loss. Always absent in predatory Onychopode and Haplopoda. Shape o f fo o d groove 0= deep and narrow (As, Ct, Ap); 1= broadly V- or U-shaped and shallow (No, La, Sp, Cy); 2= no true food groove (Ha); 3= no food groove (On). Sd: from a deep and narrow food groove to a broad groove or no groove at all (in predators). Structure o f the heart 0=with 11 pairs of ostia, corresponding to 11thoracic segments (As, No); 1- with four pairs of ostia (Sp, Cy); 2= with three pairs of ostia (La); 3= with two ostia- spherical, ovoid or fusiform (Ha, Ct, Ap, On), Sd: reduction of number of ostia from 11 to two. Ventral ganglia 0= ventral ganglia not coalesced, forming a scalari- form nerve chain (As, No, La, Sp, Cy, Ct, Ap); 1= ventral ganglia more or less coalesced into a single mass (Ha, On). Sd: from a ladder-shaped nerve chain to a concentration into a single gangliar mass in predators. Shape o f ovaries 0= tubular, with or without sacculiform dilatations (As, La, Sp, Cy, Ha); 1= sacculiform and more or les elongated (Ct, Ap, On); 2= ramified (No). Sd: from a tubular to a saccular, more concentrated shape. The Notostraca stand apart. 5c m andibular muscles in adults 0= present (As, La, Sp, Cy, Ha, Ct, On and Ap- except Anchistropus and Pseudochydorus); 1= absent (No). Sd: the 5c muscle is only missing in the Notostraca and in two genera of the Anomopoda (Fryer, 1988; Olesen, 1998). Type o f maxillules 0= unsegmented, more or less reduced, with some spines (As, La, Sp, Cy, Ct, Ap, On); 1= two- segmented, robust and denticulated, closely associated with labrum (No); 2= absent (He). Sd: reduction and loss. Notostraca form a special case. Position o f ovaries 0= located in the 4abdomen' on either side of gui ( As, Ha); 1= surrounding the gut from the first lo the I 8th segment (La, Sp, Cy); 2= located in the thorax' on either side of the gut (No, Q, Ap, On ). Sd: progressive limitation of ovaries to specified body parts (first to abdomen, nest to thorax). Position o f fem a le gonopore 0= ventral (an unpaired opening in the median ovisac in As; openings at the base of trunk limbs 11 in No, Sp and, after Linder, 1945 in La too); I - dorsolateral (oviducts open directly to the brood pouch in Cy, Ha,

13 203 Ct, Ap, On). Sd: from a ventral to a dorsal position, to open directly into the dorsal brood pouch. Type o f restin g eggs 0 = not enclosed in a case made from the carapace (clutches composed of numerous eggs, spherical, drought-resistant, with several protective layers in As and No; up to 2000 small eggs, usually spherical, produced in clumped masses and shed at moult in La and Sp; few spherical and transparent eggs with little vitellus and double protective case, shed free from brood pouch in Ha; up to 20 small eggs surrounded by oviduct-derived secretion and shed freely in Ct; usually clutches of two eggs carried temporarily in brood pouch which is shed freely in On (Fryer, 1987a; Thidry, 1996); 1= enclosed in case made in whole or part of old carapace (simplest in Macrothricidae, most elaborate ephippium in Daphniidae); up to 13, usually 1-2 large eggs in each ephippium in Ap (the homology between the anomopod and cyclestherid ephippium is uncertain). Sd: more and more elaborate protection by envelopes (including elements derived from the carapace in the case of an ephippium) in parallel with a reduction in the number of eggs produced. Position o f eggs or em bryos 0 - in ventral median ovisac (modified i 2th trunk limb) (As); 1= encapsulated in cxopod of trunk limbs 11 (No); 2= attached to dorsal extension of exopod of certain trunk limbs (eggs in La and Sp, embryos in Cy); 3= in dorsal brood pouch, not attached dorsally, situated under the carapace (eggs and embryos in Ha, Cl and Ap); 4= in a dorsal brood pouch that is a membranaceous envelope closed to the exterior (On). Sd: from the ventral position of eggs carried in structures that are modified legs to a dorsal position open enclosed to the exterior (see also Olesen, 1998). D evelopm ent in ovisac/ brood pouch Os with free-swimming larval instars (As, No, La, Sp); I - without larval stages (Cy, Ha, Ct, Ap, On). Sd: from a development with nauplii to a direct development in the brood pouch. D evelopm ent from resting eggs 0 = with larval stages (As, No, La, Sp, Ct, Ha), 1= without larval stages (Cy, Ap, On). Sd: from a development with larval stages to a development without such stages. Nährboden ( placenta/) 0= absent (As, No, La, Sp, Cy, Ha, Ct except Penilia, Ap except Moininae). 1= present (On). Sd: partheno- genetic eggs nourished in brood pouch by a placenta in all Onychopoda (Fryer, 1987a). O pening o f vasa deferentia (sperm iducts) 0= immediately behind trunk limbs (As, Ct, On); 1= on J 1th pair of trunk limbs (No, La, Sp, Cy); 2= on last segment of trunk (separately on last segment of abdomen in Fia; at distal end of postabdomen in anomopods except Eurycercus). Sd: from opening between or immediately behind the limbs to opening near the tip of the postabdomen, through a simple pore or via a penes. Penes 0= present (paired in As; paired in Ct except in Sida:, mounds or paired penes in On); 1= absent (paired genital pores in No, La, Sp, Cy, Ha); 2= absent but postabdomen modified, often markedly, for copulation (Ap except Eurycercus where postabdomen unmodified, and Leydigia, with unpaired penes between end- claws; however, because of unusual position, the latter is not considered homologous to the penes elsewhere - see Olesen, 1998). Sd: from simple gonopores, to a pair of penes, to a postabdomen modified for copulation, N um ber a n d type o f larval stages 0= two or three larval stages: nauplius, metanauplius and heliophora (As, No, La, Sp, Cy); 1= one larval stage, the metanauplius (Ha); 2= no larval stages. Resting and parthenogenetic eggs hatch as small replicas of the adult (Ct, Ap, On), Sd: reduction of the number of larval stages, up to their complete loss. Cladistic analysis Constructed on evidence of only apomorphies, our cladogram aims at the identification of monophyietic groups, as well as their parental relationship (Figure 2). Numerous plesiomorphies shared by the Anostraca, Notostraca, Laevicaudata and Spinicaudata (4, 11,12, 13, 24, 28, 31, 34, 35, 37, 38, 39, 42), plus the plesiomorphie characters shared by the Anostraca and the Notostraca (5, 6, 10, 14, 16, 17, 18, 19, 20, 21, 22, 30) and those common to Anostraca, Laevidaudata and Spinicaudata (8, 25, 26, 27, 32) show that the

14 204 anostracan and phyiiopod lines have evolved in parallel, and that these represent the oldest branchiopods. They represent a parallel evolution of homologous organs. Such a parallelism suggests a common origin (Vandel, 1943). The Anostraca have the largest number of plesiomorphisms (42 - see Table 1), They are considered the most primitive branchiopods, close to the common ancestor and constitute the sister-group of the phyllopods, which is why we chose them as an outgroup. Also the other primitive groups have numerous plesiomorphies: Notostraca 25, Laevicaudata 18 and Spinicaudata 19 (Table 1). The Cyclestherida, with 18 plesiomorphies, are also primitive. The Haplopoda have only nine plesiomorphies, the Ctenopoda 15, the Anomopoda 11, and the Onychopoda 12 (Table 1). Sets of apomorphies (1, 2, 3, 7, 9, 15, 23, 36) are shared by the Notostraca, Laevicaudata, Spinicaudata, Cyclestherida, Haplopoda, Ctenopoda, Anomopoda and Onychopoda, while characters 5,6,10, 16, 17 and 30 are common to all these groups without the Notostraca (Table 1). These characters are synapomorphies, representing the heritage from a common ancestor. We, therefore, conclude that the branchiopods of the phyiiopod line compose a monophyietic group. Apomorphies 1 (derived state I), 2 (1), 7 (1), 8 (1), 9(1), 15 (I),25(1), 26(1), 27(1), 32(2) and3 6 (1 )are typ ical of the Notostraca and characterize this order as the most primitive of the Phyiiopod line. Apomorphies 6 (derived state 1), IO (2) and 30 (2) are limited to the Laevicaudata; 10(1) is specific to Spinicaudata. The Cyclestherida have no exclusive apomorphy and require a separate discussion. This group shares two apomorphies with the Spinicaudata only (of which they are present considered a family); 1 (derived state 2) and 30 ( 1). It shares five apomorphies with only the Laevicaudata plus Spinicaudata; 2(2), 9 (2), 14 (1), 33 (1) and 36 (2). It also shares a single apomorphy with the Ctenopoda and the Anomopoda, 3 (2), and three with the Haplopoda, Ctenopoda and Onychopoda (=the Cladocera s.l): 24 (1), 34 (1) and 37 (1). It follows from this that the group occupies an intermediate position between Laevicaudata and Spinicaudata on the one hand, and between the Haplopoda, Ctenopoda, Anomopoda and Onychopoda on the other hand. Morphologically, it is somewhat closer to the Conchostraca than to the Cladocera, as seen from our cladogram (Figure 2). For this reason, we here separate the Cyclestheridae in the new order Cyclestherida, but maintain it within the superorder Conchostraca. The apomorphies that characterize the Haplopoda are more numerous than those of the other groups, even the Notostraca: 1 (derived state 4), 3 (3), 5 (3), 6 (4), 8 (4), 10 (4) 11 (1), 13 (1), 15 (4), 25 (2), 27 (2), 29 (2), 42 (1). On this evidence, we separate the Haplopoda from the Cladocera s. I. in the new super- order Leptodorida, at the same rank as the Sarsostraca, Calmanostraca, Conchostraca and Cladocera (see also Calmanostracan line section). Only two, yet significant apomorphies separate the Ctenopoda 'from all other branchiopods: 4 devised (state 1) and 22 (2). The Anomopoda, in turn, are characterized by the following six apomorphics: 4 (derived state 2), 6 (3), 8 (2), 22 (3), 28 (I) and 41 (2). The Onychopoda are distinctive by I (5), 3 (4), 6 (5), 7(4), 8 (3), 9 (4), 15 (3), 29 (3), 36 (4) and 39 (I). The Onychopoda also share two apomorphies with the Haplopoda, Ctenopoda and Anomopoda: 2 (3), and 30 (3); four with Ctenopoda and Anomopoda: 13 (2), 32 (1 ), 38 ( 1), and 42 (2); four with the Haplopoda: 4 (3 ), 12 (2), 28 (2), and 31 (1). All these synapomorphies reveal a degree of relatedness between the Leptodorida and Cladocera. Discussion Our cladogram (Figure 2) contains eight cladistic nodes. The principal branehiopod apomorphy is that proposed by Walossek ( 1995) complex postmandibu- lar filtering apparatus with sternal food groove. Sarsostracan (anostracan) line Of the branehiopod ancestor (Figure 2, node I), two branches detach: an anostracan, and a phyiiopod line. The main anostracan-linc apomorphies are: compound eyes external, raised in front, and caudal setae absent (characters 15 and 23). From (his lineage, Rehbachiella detached in the Upper Cntuhrium (Figure 1, node 3 and Figure 3). The Devonian saw the rise and decline of the Lepidoearididae, part of the fossil order Lipostraca (Figures 1 and 3). According to Taseh (1969) true Anostraca also appeared in the Devonian, while Walossek (1995) pushes the Euanostraca up to the Upper Jurassic. The orders Anostraca and flipostraca are combined in the superorder Sarsostraca. The synapomorphy uniting holti orders is the reduced lateral expansion of the head shield rims (Walossek, 1995). More details on the evolution of the anostracan line can be found in the papers by Walossek ( 1993, 1995).

15 205 C a lm a n o stm c a n line The phyiiopod line is comprised of the Calmanostraca, Conchostraca, Leptodorida and Cladocera (s.str.), each with the value of a superorder (Figures 2 and 3). This lineage has the following main synapomorphies: compound eyes internal, usually situated on antero- dorsal or frontal part of head, and caudal setae present (characters 15 and 23), Of the ancestral phyiiopod (Figure 2, node 2), two branches took off: a ealmanostraean, and a conehostracan line. The main apomorphies o f the ealmanostracans are a univalved eapapaee, a dorsally covered head and anterior part of trunk, and a terminal pair of mulitarticulate furcal rami (characters 1 and 5). According to Walossek (1995), the Notostraca (known since the Carboniferous) and tile Kazacharthra (Upper Triassic/Lower Jurassic) are sister-taxa, by their loss of the iiltratory habit of the anterior trunk limbs, flattening of the anterior zone of the body, loss of a ventral food groove, a plate-shaped labrum, cirriform furcal rami and polymetamery of the trunk, all of which support the validity of the Calmanostraca as a monophyietic taxon (Figure 1). C onehostracan line O f the ancestor of the Conchostraca (Figure 2, node 3), a branch detached towards the Laevicaudata and the Spinicaudata (Figure 2, node 4) and another one towards the Cyclestherida (Figure 2, node 5). The main apomorphies of the conehostracan line are: carapace bivalved, enclosing trunk and head, or only the trunk, or secondarily reduced to a dorsal brood pouch; a terminal pair of claws, or a simple furca, often secondarily absent (characters I and 5; Figure 2, nodes 2 aruj 3). The principal apomorphy uniting the Laevicaudata and the Spinicaudata consists of two unfused eyes, while that of the Cyclestherida, Lcpto- dorida and Cladocera consists of two fused eyes in adults (character 24, Figure 2, nodes 3 and 5). It is also important to underscore the fact thai reproduction in the Laevi- and Spinicaudata is exclusively gamo- genelie, and includes larval stages. In contrast, the Cyclestherida, Leptodorida and Cladocera have two modes o f reproduction, but predominantly partheno- genetie without larval stages (see character 42 and Figure 2). A m ajor character, restricted to the Conchostraca, and giving Lhem an ontogenetic uniqueness among the branchiopods, is a planktonic larva, the heliophora, described by Botnariuo (1948). It appears after 3-4 larval moults and marks the transition of the naupliar to the bivalved from. Botnariuc & Viña Bayes (1977) state that heliophora means bearer of a lip and that the species Cyclestheria hislopi takes an exceptional position among conchostracans with respect to this feature. Roessler ( 1995b) studied the ecology and life cycle of Cyclestheria hislopi in Colombia but missed the paper by Botnariuc & Vina Bayes (1977) on Cuba. It showed that C. hislopi has two modes of posternbryonic development: one in water (predominantly in ephemeral pools), with the heliophora stage present, and one inside the brood pouch (in permanent waters), without heliophora stage. In the second case, the metanauplius directly transforms to a bivalved stage, giving the false impression that C. hislopi has only two larval stages. This double ontogenetic pathway represents an adaptation that widens the ecological valency of the species and helps to understand its wide geographic range. Life in intermittent waterbodies, with the production of drought-resistant embryos that subsequently have a free (autonomous) development is the rule in conchostracans. It is, therefore, probable that the pathway of the heliophora stage came first, with larval development inside a brood pouch a later adaptation to life in permanent water. This appearance of viviparity (Botnariuc & Vi na Baes, 1977) is also common in many cladoceran species. Reproduction in C. hislopi is predominantly parthenogenetic, with males very rare (Olesen et al., 1997). The line of the conehostracan ancestor appears to have had a long evolution (Figure 3). One lineage may have detached from the common trunk in the Silurian to produce the order Laevicaudata. But, curiously, the most ancient fossils of Lynceus only appear in the Lower Cretaceous (Taseh, 1969; Fryer, 1987a). Another lineage detached in the Lower Devonian (Taseh, 1969; Fryer, 1987a) or Upper Silurian (Walossek, 1993, 1995), and gave rise to the Spinicaudata. This lineage is represented by fossils of Cyzicus already in the Lower Devonian and is known by six fossil families (Ipsiloniidae from the Devonian tilt the Lower Cretaceous; Asmussiidae from the Devonian till the Upper Cretaceous; Leaiidae from the Middle Devonian till the Lower Cretaceous; Vertexiidae from the Lower Carboniferous till the Upper Trias; Estheriei- lidae from the Upper Carboniferous till the Lower Cretaceous; Pemphilimnadiopsidae during the Upper Carboniferous only (Taseh, 1969), and by three extant families (Cyzicidae, Lepestheriidae and Limnadiidae (Taseh, 1969; Roessler, 1995c; Thiéry, 1996).

16 206 The reason we think that the Laevicaudata detached from the common conehostracan trunk earlier than the Spinicaudata and Cyclestherida, lies (Botnariuc, 1947; Botnariuc & Orghidan, 1953; Botnariuc & Vina Bayes, 1977) in the shape of the cyclestheriid valve, which is distinctly globular, resembling that of the Lynceidae in morphometry. The presence of a single pair of prehensile appendages in males is another character that unites both, even if the origin of their building blocks is different. In the genus Cyzicus (Spinicaudata: Cyzicidae), the apical claw is a transformed exopodite. Its club (or hook) is derived from a transformation of endite IV. The endopodite constitutes the zone of insertion of the claw. The palp of the endopodite is laterally displaced and the endital palp situated on endite IV remains as the palp of the endopodital club (Botnariuc, L947). In Lynceus (Laevicaudata: Lynceidae), the apical claw is a transformed exopodite, like in the preceding genus. Here, however, the club of the endopodite is derived from endite III, not from endite IV as in Cyzicus. The endite IV and the endopodite are laterally displaced and have become palps of the prehensile appendage. Consequently, neither the palps of the prehensile limb nor the club of the endopodite of the Lynceidae can be considered as homologous to the equivalent pieces in the Cyzicidae. In Cyclestheria (Cyclestherida), the apical claw is again derived from a transformed exopodite. Here, the club belongs to endite IV and is, therefore, homologous to that of the Cyzicidae, while the palp plays the role of a prehensile limb. Consequently, this organ is homologous to that of the Lynceidae. Fryer (1987a) considers this case an excellent example of homoplasy, that would not have been revealed had the development of the appendage in question not been studied. According to Botnariuc & Vina Bayes (1977), the important fact that both the lynceid and cyclestheriid males have a single pair of prehensile limbs suggests the possibility that both families became detached from the common trunk of the conchostracans prior to the différenciation of the second pair of prehensile limbs in other families. This argues in favour of the primitive nature of both groups. That the pieces of the prehensile limb of the Lynceidae are not homologous with those of the Cycles- theridae suggests both broke away from the common trunk at different times. Based upon the character of the valves (the most globular of all being that of the Lynceidae), the number of limbs, the head structure and the heliophora larva, we suggest that the first group to detach was that of the Lynceidae (Figure 3). For more recent observations on the external morphology of the male of Cyclestheria hislopi, and a comparison of male claspers between Cladocera and Conchostraca (including its bearing on the phylogeny of the branchiopods, see Olesen et al., 1996). Leptodorid line The ancestor of the Cyclestherida sent a branch (Figure 2, node 5) to the extant eyclestheriids, and another to the Leptodorida and the Cladocera (node 6). The main apomorphies of the Cyclestherida are: a bivalved carapace with a hinge and 16 pairs of trunk limbs, as opposed to the apomorphies uniting Leptodorida and Cladocera: carapace bivalved without a lunge, and 4-6 pairs of trunk limbs (characters 2 and 9). The Leptodorida have the following apomorphies: first pair of trunk limbs in male devoid of a clasping hook and metanauplius present, as opposed to the apomorphies for the cladoceran line: only first pair of trunk limbs in male with clasper, and larval stages absent (characters IO and 42; nodes 6 and 7 of Figure 2). The derivation of the Leptodorid lineage from that of its common ancestor with the Cyclestherida seems to have happened in the Devonian or later (no fossil record available) (Figure 3). This ancestor probably had a laterally compressed carapace without hinge, enclosing the body; the eyes were united into a single organ; the antennae biramous and natatory; the limbs serially similar and foliaceous; the food-groove well- developed; reproduction predominantly by parthenogenesis and without resting eggs; a dorsal brood pouch and metanauplius present. We suppose that this ancestor gave rise to the sole extant representative of the Haplopoda, Leptodora kindtii, considered by Brooks (1959) to be nothing but an unusual conehostracan: the group comprising all of the Cladocera except Leptodora kindti (Focke) is named Eucladocera by Eriksson, and in some ways Leptodora is more like an aberrant conehostracan than a derivative of the Eucladocera. This soft-bodied species does not fossilize well, and only subfossil - though characteristic - mandibles are known from Lake Windermere, England (Taseh, 1969). According to Eriksson (1934), the size and segmentation of the body, the head position, the structure of the antennae and the digestive tube, the mode of insertion of the brood sac and the metanauplius stage

17 207 arc all primitive characters, indicative of the origin of this taxon. Clearly, all modifications of the ancestor of the Cyclestherida leading to the Leptodorida relied an adaptation of the latter to a predatory way of life. Such are, for example: the reduction of the carapace to a dorsal brood sac in females (liberates the legs and increases swimming speed); the transformation of the legs from foliaceous to cylindrical (stenopodous), without fi l ter combs; the total reduction of the exopocl- ites; the modilication of the mandibles from a crushing to a biting type; loss of the two maxillae and of the food groove. though probably later than the ctenopods. This, the Anomopoda, left the fossil record discussed above and currently includes a large number of species in at least IO families (Daphniidae, Ilyocryptidae, Eurycercidae, Sayciidac, Macrothricidae, Bosminidae, Chydoridae, Ophryoxidae, Acantholeberidae and Neothrieidae, see Dumont & Silva-Briano, 1998 and Figure 3) A third lineage detached, again in the Permian, and probably before the separation of the Ctenopoda and of the Anomopoda (Figure 3). This, the Onychopoda, has left no true fossil record (except subfossils of cf. Polyphemus from England: Taseh, 1969) and is currently composed of the three families Polyphemidae, Podonidae and Cercopagiclae, C ladoceran line Of the ancestor of the Cladocera (Figure 2, node 7) a branch leads to the Ctenopoda and the Anomopoda (node 8), and another one lo the Onychopoda. The principal apomorphies uniting Ctenopoda and Anomopoda are: carapace enclosing only the trunk and trunk limbs foliaceous, as opposed lo the following apomorphies for the Onychopoda: carapace reduced to a dorsal brood pouch, and trunk limbs stenopodous (characters I and 8; Figure 2, nodes 7 and 8 ). The derivation of the cladoceran lineage (s.str.) of that of the ancestor of the cyelcsleriids probably took place in the Devonian or Carboniferous. According to Smirnov (1970, 1971), typical cladocerans already existed in the Permian: Propleuroxus freyi and four fossil species o( Archedaphnia occur in Permian sediments of Transbaikalia (Figure 3). In more recent deposits, dated lo the Oligocène, ephippia of Daphnia have been found (Frey, 1964, 1967), and ephippia of M oina occurred in niocene layers (Conidea 1968) (Figure 3). Two finds from the Lower Cretaceous should also be mentioned: ephippia of Simocephalus (Frey, 1967, 1993) and the fossil species Prochydorus rotundus from Mongolia (Smirnov, 1992, 1996). For the latter, Fryer (1995) proposed a new subfamily, the Proehydorinae (in replacement of Smirnov s family Proehydoridae). The lineage of the cladoceran ancestor evolved in three directions (Figure 3). A first lineage may have detached from the common trunk in the Permian (leaving no Ibssi! record because of its soft integument), leading to the order Ctenopoda, currently represented by the families Sididae and Holopodidae. A second, and most important, lineage also became detached from the common trunk during the Permian, C onclusions A cladistic analysis involving 42 characters revealed a common ancestor to the nine extant groups of branchiopods, strongly suggesting that it constitutes a monophyietic group. The Anostraca (outgroup) are the most primitive of the nine, characterized by the largest number of plesiomorphies. vsynplesiomorphies between the anostracan and the phyiiopod lines suggest a parallel evolution of homologous organs. The prehensile limbs of the male Cyclestherida (Cyelestlieria) and the Laevicaudata (Lynceus) are an excellent example of homoplasy. The characters thai allow a separation between the Spinicaudata and the Cyclestheridae on the one hand (see Fryer, j 987a) anti characters shared with the cladocerans, on the other hand, justify the creation of a new order, the Cyclestherida. À large number of aulapomorphies separate the Haplopoda from the three other groups of cladocerans (Ctenopoda, Anomopoda, Onychopoda) and justify the creation of a new superorder, the Leptodorida. The course of evolution from the most primitive lo the most highly evolved anomopoda and onyehy- pods is characterised by a simplification and reduction of certain complex structures, inherited from the ancestral branehiopod, as well as by Ihe progressive evolution of structures adapted to life in epigean and subterranean aquatic habitats. The main evolutionary tendencies are: I, Conservation of numerous primitive characters in the extant Anostraca.

18 Reduction of the body segmentation by a fusion of somites, culminating in a total loss of these segmentation in the onychopods. 3. Modification of the carapace to engulf the brood pouch of parthenogenetic females, to form an ephippium in gamogenetic females or its reduction to an incubator sac (in females of the haplopods and onychopods). 4. Fusion of the eyes to a single medial organ (Leptodorida and Cladocera s.s.), most advanced in raptorial species (Haplopoda and particularly Ony- chopoda)(buteyes may be reduced in subterranean species). 5. Reduction of the number of foliaceous trunk limbs (to 5-6 in the ctenopods and anomopods, to 4 in the onychopods), and various specialisations to filter, crawl, brush, for chemo- and mechanorecep- tion (Anomopoda) and for prey capture (Onychopoda). 6. Conservation of the swimming antennae as a means of locomotion in the Conchostraca, Leptodorida, and Cladocera s.s. The antennae are more reduced in benthic and hypogean forms, particularly chydorids, as an adaptation to their mode of life. 7. Reduction of the postembryonic larval stages, up to their total absence in the Cladocera s.s. 8. Reduction of bisexual reproduction (up to a complete disappearance in certain tropical anomopods), or alternation with parthenogenetic reproduction for ecological reasons (Leptodorida and Cladocera s.s.). P roposed phylogenetic classification Superclass Crustacea Lamarck, 1801 Class Branchiopoda Latreille, 1817 (as defined by Caiman, 1909) Superorder Sarsostraca Taseh, Order Anostraca Sars, Family Artemiidae Grochowski, Family Polyarthemiidae Simon, Family Branchrnectidae Daday, Family Branchipodidae Milne-Edwards, Family Chirocephalidae Daday, Family Artemiopsidae Brtek, Family Linderiellidae Brtek, Family Streptocephalidae Daday, Family Thamnocephalidae Packard, t Family Gilsonicarididae Van Straelen, 1943 Note: This ten-family system reflects the views of Brtek (1997). However, recent molecular work using the base sequence of the SSU operon (Weekers et ah, in press) has shown that the Branchipodidae are poly- phyletic and represent two or three families, while also the Thamnocephalidae may need to be split in two taxa of family level. Moreover, the Parartemiidae combine into a single clade with the Artemiidae (the Subordo Artemiina), opposed to all other anostracans (the Subordo Anostracina). 2.f Order Lipostraca Scourfield, t Family Lepidoearididae Scourfield, 1926 Superorder Calm anostraca Taseh, Order Notostraca Sars, Family Triopidae Keilhack, t Order Kazacharthra Novojilov, t Family Ketmeniidae Novojilov, 1957 Superorder C onchostraca Sars, Order Spinicaudata Linder, Family Cyzicidae Stebbing, Family Leptestheriidae Stebbing, Family Limnadiidae Burmeister, f Family Ipsiloniidae Novojilov, f Family Asmussiidae Kobayashi, t Family Leai idae Raymond, t Family Vertexidae Kobayashi, t Family Estheriellidae Kobayashi, f Family Pemphilimnadiopsidae Taseh, Order Laevicaudata Linder, Family Lynceidae Sayce, Order Cyclestherida, new order 3.1. Family Cyclestheriidae Sars, 1887 Superorder Leptodorida, new superorder 1. Order Haplopoda Sars, 1865 LÍ. Family Leptodoridae Lili jeborg, 1861 Superorder Cladocera M ilne-edwards, 1840 (sensu strictu, as defined in this paper) 1. Order Ctenopoda Sars, 1865 (=Sidoidca Baird,

19 209 i 850, emend. Brooks, 1959) 1.1. Family Sididae Baird, 1850 (emend. Sars, 1865) 1.2. Family Holopedidae Sars, Order Anomopoda Sars, 1865 (= Chydoroidea Dy- bowski & Grochowski, 1894, emend. Brooks, 1959) 2.1. Family Daphniidae Straus, 1820 (emend. Sehoedler, 1858) 2.2. Family Bosminidae Baird, 1845 (emend, Sars, 1865) 2.3. Family Ilyocryptidae Smirnov, Family Eurycercidae Kurz, Family Sayeiidae Frey, Family Chydoridae Dybowski & Grochowski, 1894 (emend. Stebbing, 1902) 2.7. Family Ophryoxidae Smirnov, Family Aeantholeberidae Smirnov, Family Macrothricidae Norman & Brady, Family Neothricidae Dumont & Silva-Briano, Order Onychopoda Sars, 1865 (^Polyphcmoidea Baird, 1845, emend. Brooks, 1959) Family Polyphemidae Baird, Family Podonidae Mordukhai-Bollovskoi, Family Cercopauidac Mordukhai-Bollovskoi, 1968 Principal diagnostic characters of the live superorder,s The present study showed that it is necessary to distinguish live superorders of branchiopods. In the fob lowing paragraphs we list (heir principal diagnostic characters (main source of information: Fryer, 1987a). Superorder Sarsostraca lasch, 969 Body elongated, divided into two lagiuala: a cephalum and a po.sfeeplialie part composed of 18* 27 segments, plus a telson. No carapace, Eyes raised on front. 1lead short. Labrum well developed. Mandibles of the rolling type. Anntenules simple, cylindrical. Trunk limbs up lo 21 pairs, fuliuceotis or modified, Food groove deep and narrow. Paired caudal setae absent. Nauplius with large labrum. Length of adult c. 3 mm in Lipostraca and 8 35 mm (maximum 100 mm) in Anostraca. Fresh or continental saline waters, often in ephemeral pools. Efficient swimmers. Superorder C alm anostraca Taseh, 1969 Body elongated, Head composed of few somites. Trunk composed of numerous basically cylindrical segments1(see Fryer, 1987a, p. 379), not homologous 10 those of other branchiopods (25-44 segments, of which the last 4-14 lack appendages in the Notostraca and apparently abdominal segments lack appendages in Kazacharthra) and telson. A dorsal, uni- valved, shield-like carapace, covering the head and anterior portion of trunk. Eyes essile, paired. Antennae uniramous, vestigial or even absent (unknown in Kazacharthra). Trunk limbs non-liltratory, similar in shape but different in structure from those of other branchiopods (35-71 pairs in Notostraca and 11 pairs in Kazacharthra). Nauplius and metanauplius present (uncertain in Kazacharthra). Length variable (up lo mm in Notostraca and about 100 nun in Kazacharthra). Fresh and sometimes brackish water. The Notostraca arc non-filtering, benthic omnivores. Superorder Conchostraca Sars, IS67 Body short. Trunk with from 10 (in Laevicaudata) Lo up to 32 segments (in Spinicaudata), all bearing appendages, and a telson (posiabdomen). Paired caudal setae present. Carapace bivalved, with hinge. Head with rostrum, l'iyes paired, sessile, more or less eon- lluent: ocellus placed below eyes, large, composed of four cups. Labrum large, llcshy. Antennules more or less elongate, of 1-2 segments (in Spinicaudata), or superficially 2-4 segmented (in Laevicaudata). Antennae large, biramous, natatory, much larger than antennules. Mandibles of grinding type. Trunk limbs foliaceous, directed venlrally and showing considerable serial homology (16-32 pairs in Spinicaudata, in Laevicaudata). Food groove broadly V- or U-shaped. Alimentary canal straight, without loops, witti convoluted anterior caeca that occupy much of the head. Genital ducts opening on I 1th segment. Eggs small and numerous (exceeding 2000 in some cases). Three poslembryonic stages present: nauplius, luetaimuplius and heliophora. Length of females up lo 17 mm in Spinicaudata and 7 mm in Laevicaudata (bill males smaller). Freshwater, mainly ephemeral pools (but Cyclestheria also in permanent waters). Superorder Leptodorida, new superorder Body strongly elongate, hyaline and translucent* Head elongated, slender, cylindrical. Thorax short with cryptic segmentation, bearing six pairs of cylindrical

20 210 legs without exopodites or branchial epipodites, and carapace (in females) reduced to a dorsal brood sac. Abdomen* elongate, cylindrical, distinctly segmented into three segments and telson ending in two claws. No caudal setae. Eye single (in adults), filling anterior part of head. Ocellus lost in adult stage. Labrum short and swollen. Mandibles styliform, not grinding. Maxillules and maxillae absent. No true food groove. No anterior caeca. Anus opening at end of telson. Antennae biramous and natatory, with four segments per branch. Antennules uniramous, short in female, elongate in male. Reproduction by parthenogenesis and bisexual with production of resting eggs. A metanauplius only present. Male with first trunk limb modified into a (female) clasping organ. Length adult female 7 11 mm (exceptionally up to 18 mm), and male 7-9 mm. Freshwater, planktonic predators. Superorder Cladocera M ilne-edw ards, 1840 (s.sin) Body short, of few segments, tagmosis mostly obscure; body terminating in a strong telson, named postabdomen (rather small in the onychopods), armed with a pair of terminal claws and with a pair of sensory setae on a proeminence (which may be small, long or very long in the Onychopoda). Carapace bivalved without a hinge, enclosing trunk and its appendages but not the head (except Onychopoda, where the carapace is reduced to a dorsal brood sac). Head short. Labrum fleshy. Eye single with several lenses, occupying most of the head in the Onychopoda. Ocellus usually present, but lost in the Onychopoda. Antennules tubular in female. Antennae biramous, natatory (secondarily uniramous in female of Holopedium ), with 2, 3 or 4 segments per branch. Mandibles of grinding type, but modified for biting in Onychopoda. Maxillae reduced or absent. Trunk limbs 4-6 pairs, with exopodite (lost in Cercopagidae); all filtratory and similar in Ctenopoda; modified to perform various functions such as filtration, grasping, scraping, guiding or sweeping particles, locomotion and even chemo- and mechanoreception in Anomopoda; modified to capture prey in the Onychopoda. Pood groove deep and narrow, and no true food groove in Onychopoda. Alimentary canal straight or with a loop. Reproduction either bisexual or by cyclical parthenogenesis. Resting eggs present. Postembryonic larval stages absent. Few arctic daphnids and several Caspian and oceanic cercopagids are obligate parthenogens. Males smaller than females and their antennules mostly modified for clasping; their first trunk limb end in a clasper. Length from 0.2 nun (male of Alonella nana) to 6 mm (female of Daphnia magna) in Anomopoda, but only 4 mm in Ctenopoda and up to 12 mm in Onychopoda with long caudal processes (Cercopagidae). 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