Colony formation in the Cheilostomatous Bryozoan Fenestrulina Malusii var. Thykeophora

Transcription

1 New Zealand Journal of Marine and Freshwater Research ISSN: (Print) (Online) Journal homepage: Colony formation in the Cheilostomatous Bryozoan Fenestrulina Malusii var. Thykeophora D. P. Gordon To cite this article: D. P. Gordon (1971) Colony formation in the Cheilostomatous Bryozoan Fenestrulina Malusii var. Thykeophora, New Zealand Journal of Marine and Freshwater Research, 5:2, , DOI: / To link to this article: Published online: 30 Mar Submit your article to this journal Article views: 56 View related articles Citing articles: 5 View citing articles Full Terms & Conditions of access and use can be found at

2 342 [JUNE COLONY FORMATION IN THE CHEILOSTOMATOUS BRYOZOAN FENESTRULINA MALUSII VAR. THYKEOPHORA D. P. GORDON* Leigh Marine Laboratory, University of Auckland, Private Bag, Auckland, New Zealand (Received for publication 14 April 1970) ABSTRACT The early stages of colony formation of Fenestrulina malusii var. thyreophora are described, and notes on two other species are included for comparison. In Fenestrulina, early budding patterns are very variable, although some patterns are commoner than others. At the 3-zooid stage of colony formation there is usually temporary suppression of budding on one side, with the result that the three first-generation zooids produced from the ancestrula arise 1, 2, 4 in the commonest budding sequence rather than 1, 2, 3; budding patterns may be considerably modified when colonies are obstructed. In Fenestrulina and Eurystomella foraminigera the first zooid budded from the ancestrula lies in the distal midline whereas the second zooid occupies this position in Crassimarginatella papulifera. In all three species the proximal periancestrular zooids are not budded directly from the ancestrula but belong to the third zooidal generation. INTRODUCTION The patterns of budding during the development of bryozoan colonies are very variable. For a number of species, the early stages following the establishment of the ancestrula by larval metamorphosis have been described by many workers, but no one has ever determined the number and frequency of occurrence of the growth patterns that a species may exhibit. This paper describes the colony development (astogeny) of an incrusting cheilostome to demonstrate the variability in budding patterns found in a single species. Notes on two other species are included for comparison. The ways in which zooid buds are formed during astogeny is described by Gordon (in press). MATERIALS AND METHODS The three species Fenestrulina malusii (Audouin) var. thyreophora Busk, Eurystomella foraminigera (Hincks), and Crassimarginatella papulifera (MacGillivray) were collected from an intertidal rocky platform at Goat Island Bay, near Leigh, North Island, New Zealand. During the summer of Fenestrulina larvae settled in large numbers on a variety of surfaces. The numbers and frequency of occurrence of different budding patterns during colony formation were recorded from the numerous ancestrulae and young colonies available. *Present address: Biology Dept, Dalhousie Univerity, Halifax, Nova Scotia, Canada. N.Z. Journal of Marine and Freshwater Research 5 (2) :

3 1971] GORDON COLONY FORMATION IN Fenestrulina 343 Some colonies kept in aquaria at the Leigh Marine Laboratory were followed through a succession of budding stages, but most records of these stages were obtained by microscopic examination of colonies from the shore. One can fairly quickly determine the budding sequences of very young colonies according to the development of the feeding polypides and the degree of calcification of the frontal walls. Sequences are easy to determine in this way up to stage V in colony development. Only for a small number of colonies could the sequences of development at and beyond stage V be recorded. RESULTS Astogeny of Fenestrulina malusii var. thyreophora Zooid development is sequential in the early stages, and no two zooids arise simultaneously. The ancestrula buds off the first zooid in the distal midline. The positions of the next zooid to develop, and of all the other zooids which will arise subsequently, are variable. This variability is shown in Fig. 1; there are three possible positions for zooid 2, five for zooid 3, and eleven for zooid 4. Only seven positions (two in one colony) were noted for zooid 5 because this is the stage at which accurate recording of sequences becomes difficult. At stage V zooids in different parts of a colony start to develop simultaneously. Certain growth patterns are commoner than others. In the two main patterns found in stage III (14 and 16 times) only two first-generation zooids are formed, with the suppression of one disto-lateral zooid. Such suppression of one side was noted in some species by Waters (1924). Colonies are more or less symmetrical after stage IV. There is no apparent tendency to anticlockwise development, although Medd (1966) found this condition to be common in Cretaceous membraniporine bryozoans. I have noticed it sometimes in unobstructed colonies of Crepidacantha crinispina Levinsen, Fenestrulina malusii, and Crassimarginatella papulifera. As the number of distal and disto-lateral zooids increases, new zooids are budded off proximally (Fig. 2). Zooids from both sides meet at the proximal end of the ancestrula and the colony assumes the beginnings of its later circular form. In Fenestrulina, the development of proximally directed zooids may begin immediately after the formation of the first zooidal generation (bottom of stage V in Fig. 1). However, development of the proximal zooids may be postponed until there are 50 or more in the colony. Thereafter, the colony usually radiates outward in centrifugal fashion, maintaining its circular form until obstructed. The patterns of growth shown in Fig. 1 are of unobstructed colonies of Fenestrulina. The budding sequence and directions of growth may be modified by external factors. Larvae frequently metamorphose against such impediments as prominences on rock surfaces or in broken polychaete tubes. Development which is impeded on one side usually proceeds in a direction which is directly or obliquely opposite to the obstructed side (Fig. 3).

4 344 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [JUNE 0 FIG. 1 Alternative budding sequences in the early astogeny of Fenestrulina malusii var. thyreophora colonies from Leigh, N.Z., A refers to the ancestrula, 1-5 refers to the order of development of the daughter zooids. The numbers beneath each colony represent the number of times that the particular sequence was recorded. The Roman numerals refer to groups of colonies arranged in the figure according to the stage at which zooid 1, 2, 3, 4 or 5 arises.

5 1971] GORDON COLONY FORMATION IN Fenestrulina 345 B FIG. 2 A 16-zooid colony of Fenestrulina malusii var. thyreophora from Leigh, N.Z., , with three zooidal generations; B diagrammatic representations of A (depicted according to the method of Harmer 1931) showing the origins of the zooid generations and the sequences in which they arose: Zooids bi-b3 = zooids of the first zooidal generation (for b a read ba), Zooids C1-C9 = zooids of the second zooidal generation, Zooids di-ds = zooids of the third zooidal generation.

6 346 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [JUNE Astogeny of Eurystomella foraminigera The ancestrula cuts off one distal semicircular chamber from which three first-generation zooids arise. The first zooid lies on the midline, and the position of subsequent buds is variable. The proximal members of the periancestrular zooids are derived as in Fenestrulina and belong to the third zooidal generation from the ancestrula (Fig. 4). The young colony typically assumes a roughly circular shape early in astogeny by the development of the proximal zooids. Fig. 4E is a diagrammatic representation of a 20-zooid colony showing the origins of the periancestrular zooids. Waters (1925b) pictured the ancestrula of a colony from Stewart Island, but his accompanying text gave no indication of the origin of the later zooids. Astogeny of Crassimarginatella papulifera Zooid 1 is typically skewed disto-laterally to the ancestrula, but the position is variable, and the asymmetry may be left- or right-handed. Zooid 2 arises adjacent to zooid 1 and (Fig. 5) occupies the midline position that is occupied by zooid 1 in Fenestrulina and Eurystomella- Young colonies often show a tendency to anticlockwise development, but this is ultimately obliterated by the late development of the remaining periancestrular zooids and their progeny (Fig. 6). DISCUSSION The budding patterns of Fenestrulina colonies are highly variable. The only stage which is constant is stage I where the first zooid to be budded from the ancestrula always lies in the distal midline. Eurystomella behaves similarly, but in Crassimarginatella zooid 2 lies in the distal midline. At stage II in Fenestrulina, zooid 2 may arise with equal likelihood on the left or right of zooid 1; the frequencies of left- or righthand budding of zooid 2 in Fig. 1 are not significantly different (0.8 > P > 0.7). At stage III, however, there is a tendency towards suppression of one disto-lateral zooid. The difference in the observed frequencies of colonies showing the suppression and those showing nonsuppression is significantly in favour of the former (P < 0.001). Waters (1924) noted this suppression of one side in a number of species, but he considered that production of three first-generation zooids before any second-generation zooids are budded is the general rule. Fenestrulina malusii var. thyreophora is an exception to this. The asymmetry of young colonies is later obliterated by the eventual budding of the remaining zooid of the first generation and the significance of its temporary suppression is unknown. Further variations in the astogeny of cheilostomes is discussed by Boardman and Cheetham (1969). The proximal periancestrular zooids of all three species are not budded directly from the ancestrula but belong to the third zooidal generation. This origin of proximal zooids was recorded by Waters (1924; 1925a, b;

7 1971] GORDON COLONY FORMATION IN Fenestrulina 347 B FIG. 3 Modifications of the normal astogenetic sequences of Fenestrulina malusii var. thyreophora, from Leigh, N.Z., A colony obstructed by Spirorbis; B colony which arose from a larva which metamorphosed in a broken polychaete tube. Sig-10

8 348 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [JUNE FIG. 4 Stages in the astogeny of Eurystomella foraminigera, from Leigh, N.Z., A ancestrula and three zooids of the first asexual generation; B sequence of development in an obstructed colony; C Waters' (1925b) representation of a colony from Stewart Island; D 20-zooid colony showing directions of budding; E diagrammatic representation of the zooidal generations of the colony in D.

9 1971] GORDON COLONY FORMATION IN Fenestrulina 349 FIG. 5 Early stages in the astogeny of Crassimarginatella papulifera, from Leigh, N.Z., 1967-^68. A alternative positions of the first zooid budded from the ancestrula; B and C later stages of A.

10 350 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH [JUNE B FIG. 6 Crassimarginatella papulifera, from Leigh, N.Z A 20-zooid colony showing a tendency to anticlockwise development (the numbers in the zooids are not meant to imply the exact budding sequence); B diagrammatic representation of the zooidal generations of A.

11 1971] GORDON COLONY FORMATION IN Fenestrulina a, b) and Medd (1966) for a number of species, and by Cook (1964) for Conopeum reticulum, and it seems to be general in cheilostomes. Direct budding of proximal zooids from the ancestrula is known, however, and is figured by Stach (1938) for Smittina papillifera, Lagaaij (1963) for Cupuladria canariensis, and Powell (1968) for Hippopodina jeegeensis. Although the early stages of colony formation may be very variable and somewhat asymmetrical, the tendency in the older stages of the three species studied here is always towards a more or less radially asymmetrical colony. ACKNOWLEDGMENTS I am grateful to Dr W. J. Ballantine, Director of the Leigh Marine Laboratory, for use of facilities. I also wish to thank Dr W. C. Banta (Smithsonian Institution) and Dr E. L. Mills (Institute of Oceanography, Dalhousie University) for criticising the manuscript. LITERATURE CITED BOARDMAN, R. S. and CHEETHAM, A. H. 1969: Skeletal growth, intracolony variation, and evolution in Bryozoa: a review. Journal of Paleontology 43: COOK, P. L. 1964: The development of Electra monostachys (Busk) and Conopeum reticulum (L.) Polyzoa, Anasca. Cahiers de biologie marine 5: GORDON, D. P. (in press) : Zooidal budding in the cheilostomatous bryozoan Fenestrulina malusii var. thyreophora. N.Z. Journal of Marine and Freshwater Research 5. HARMER, S. F. 1931: Recent work on Polyzoa. Proceedings of the Linnean Society of London 143: LAGAAIJ, R. 1963: Cupuladria canarienis (Busk) - Portrait of a bryozoan. Paleontology 6: MEDD, A. W. 1966: The zoarial development of some membranimorph Polyzoa. Annals and Magazine of Natural History 9: POWELL, N. A. 1968: Early astogeny in Hippopodina feegeensis (Busk). National Museum of Canada Bulletin 223: 1-4. STACH, L. W. 1938: Colony formation in Smittina papillifera (MacGillivray, 1869) (Bryozoa). Proceedings of the Zoological Society of London 108B: WATERS, A. W. 1924: The ancestrula of Membranipora pilosa L. and of other cheilostomatous Bryozoa. Annals and Magazine of Natural History 14: a: Ancestrulae of cheilostomatous Bryozoa II. Annals and Magazine of Natural History 15: b: Ancestrulae of cheilostomatous Bryozoa III. Annals and Magazine of Natural History 16: a: Ancestrulae and frontal of cheilostomatous Bryozoa. Annals and Magazine of Natural History 17: b: Ancestrulae of cheilostomatous Bryozoa V. Annals and Magazine of Natural History 18: