An Overview of Animal Diversity

Figure 32.1 CAMPBELL BIOLOGY Figure 32.1a A Kingdom of Consumers TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson! Most animals are mobile and use traits such as strength, speed, toxins, or camouflage to detect, capture, and eat other organisms 32! For example, the chameleon captures insect prey with its long, sticky, quick-moving tongue An Overview of Animal Diversity Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick 2 3 4 Concept 32.1: Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers Nutritional Mode Cell Structure and Specialization Reproduction and Development! Animals are heterotrophs that ingest their food! Animals are multicellular eukaryotes! There are exceptions to nearly every criterion for distinguishing animals from other life-forms! Their cells lack cell walls! Several characteristics, taken together, sufficiently define the group! Their bodies are held together by structural proteins such as collagen! Most animals reproduce sexually, with the diploid usually dominating the life cycle! After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage! leads to formation of a multicellular, hollow blastula! Nervous tissue and muscle tissue are unique, defining characteristics of animals! The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues! Tissues are groups of similar cells that act as a functional unit 5 6 Figure 32.2-1 Figure 32.2-2 7 Figure 32.2-3 8 Blastula Video: Sea Urchin Embryonic Development (Time Lapse) of blastula Blastula of blastula Gastrulation of gastrula 9 10 Blastopore 11 Concept 32.2: The history of animals spans more than half a billion years! Most animals have at least one larval! A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis to become a juvenile! A juvenile resembles an adult, but is not yet sexually mature! Most animals, and only animals, have Hox genes that regulate the development of body form! More than 1.3 million animal species have been named to date; far more are estimated to exist! Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology! The common ancestor of all living animals likely lived between 700 and 770 million 13 14 12 Steps in the Origin of Multicellular Animals! Morphological and molecular evidence points to a group of protists called choanoflagellates as the closest living relatives to animals! The common ancestor may have resembled modern choanoflagellates 15 16

Figure 32.3 Figure 32.4 Neoproterozoic Era (1 Billion 542 Million Years Ago)! The origin of multicellularity requires the evolution of new ways for cells to adhere (attach) and signal (communicate) to each other Individual choanoflagellate Choanoflagellates OTHER EUKARYOTES! Molecular analysis has revealed similarities between genes coding for proteins involved in adherence and attachment in choanoflagellates and animals Sponges Animals 17 CCD domain (only found in animals) Fruit fly Mouse 18 Figure 32.5 19 Figure 32.5a 1.5 cm! Early animal embryos and evidence of predation have also been found in Neoproterozoic rocks Hydra Collar cell (choanocyte) Other animals! Early members of the animal fossil record include the Ediacaran biota, which dates back to about 560 million Choanoflagellate Figure 32.5b 1.5 cm 0.4 cm 20 Figure 32.6 0.4 cm Bore hole 0.1 mm (a) Mawsonites spriggi (b) Spriggina floundersi (a) Mawsonites spriggi 21 (b) Spriggina floundersi 22 23 Figure 32.7 24 Figure 32.7a Figure 32.7b Paleozoic Era (542 251 Million Years Ago)! The Cambrian explosion (535 to 525 million ) marks the earliest fossil appearance of many major groups of living animals! Most of the fossils from the Cambrian explosion are of bilaterians, organisms that have the following traits: 1 cm Hallucigenia fossil (530 mya)! Bilaterally symmetric form 1 cm! Complete digestive tract Hallucigenia fossil (530 mya)! One-way digestive system 25 26! There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota! New predator-prey relationships! Animal diversity continued to increase through the Paleozoic, but was punctuated by mass extinctions! Animals began to make an impact on land by 450 million! A rise in atmospheric oxygen! Vertebrates made the transition to land around 365 million! The evolution of the Hox gene complex 27 28 Mesozoic Era (251 65.5 Million Years Ago) Cenozoic Era (65.5 Million Years Ago to the Present)! Coral reefs emerged, becoming important marine ecological niches for other organisms! The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals! The ancestors of plesiosaurs were reptiles that returned to the water! These extinctions included the large, nonflying dinosaurs and the marine reptiles! During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates! Mammals increased in size and exploited vacated ecological niches! The first mammals emerged! The global climate cooled! Flowering plants and insects diversified 29 30 31 32

Concept 32.3: Animals can be characterized by body plans! Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits! Some body plans have been conserved, while others have changed multiple times over the course of evolution Symmetry! Animals can be categorized according to the symmetry of their bodies, or lack of it! Some animals have radial symmetry, with no front and back, or left and right Figure 32.8 (a) Radial symmetry! Two-sided symmetry is called bilateral symmetry! Bilaterally symmetrical animals have! A dorsal (top) side and a ventral (bottom) side! A right and left side! Anterior (front) and posterior (back) ends! Many also have sensory equipment, such as a brain, concentrated in their anterior end (b) Bilateral symmetry 33 34 35 36 Tissues! Radial animals are often sessile or planktonic (drifting or weakly swimming)! Bilateral animals often move actively and have a central nervous system! Animal body plans also vary according to the organization of the animal s tissues! Tissues are collections of specialized cells isolated from other tissues by membranous layers! During development, three germ layers give rise to the tissues and organs of the animal embryo! is the germ layer covering the embryo s surface! is the innermost germ layer and lines the developing digestive tube, called the archenteron! Sponges and a few other groups lack true tissues! Diploblastic animals have ectoderm and endoderm! These include cnidarians and a few other groups! Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians! These include flatworms, arthropods, vertebrates, and others 37 38 39 40 Body Cavities Figure 32.9 Figure 32.9a Figure 32.9b! Most triploblastic animals possess a body cavity! A true body cavity is called a coelom and is derived from mesoderm! ates are animals that possess a true coelom (a) ate Tissue layer lining coelom and suspending internal organs (c) Acoelomate Tissuefilled region Wall of digestive cavity (b) Psuedocoelomate Pseudocoelom Muscle layer (a) ate Tissue layer lining coelom and suspending internal organs (b) Pseudocoelomate Pseudocoelom Muscle layer 41 42 43 44 Figure 32.9c (c) Acoelomate Tissuefilled region! A pseudocoelom is a body cavity derived from the mesoderm and endoderm! Triploblastic animals that possess a pseudocoelom are called pseudocoelomates! Triploblastic animals that lack a body cavity are called acoelomates! Terms such as coelomates and pseudocoelomates refer to organisms that have a similar body plan and belong to the same grade! A grade is a group whose members share key biological features Wall of digestive cavity! A grade is not necessarily a clade, an ancestor and all of its descendants 45 46 47 48

Protostome and Deuterostome Development Figure 32.10 Figure 32.10a! Based on early development, many animals can be categorized as having protostome development or deuterostome development! In protostome development, cleavage is spiral and determinate! In deuterostome development, cleavage is radial and indeterminate (a) (b) formation Spiral and determinate Radial and indeterminate (a) 49! With indeterminate cleavage, each cell in the early s of cleavage retains the capacity to develop into a complete embryo! Indeterminate cleavage makes possible identical twins, and embryonic stem cells 50 (c) Fate of the blastopore Blastopore Blastopore Solid masses of mesoderm Folds of archenteron split and form coelom. form coelom. Digestive tube develops from blastopore. develops from blastopore. 51 Spiral and determinate Radial and indeterminate 52 Figure 32.10b Figure 32.10c Formation Fate of the Blastopore (b) formation Blastopore Blastopore Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. (c) Fate of the blastopore develops from blastopore. Digestive tube develops from blastopore.! In protostome development, the splitting of solid masses of mesoderm forms the coelom! In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom! The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula! In protostome development, the blastopore becomes the mouth! In deuterostome development, the blastopore becomes the anus 53 54 55 56 Concept 32.4: Views of animal phylogeny continue to be shaped by new molecular and morphological data! By 500 million, most animal phyla with members alive today were established 57 The Diversification of Animals! Zoologists recognize about three dozen animal phyla! Phylogenies now combine morphological, molecular, and fossil data 58! Five important points about the relationships among living animals are reflected in their phylogeny 1. All animals share a common ancestor 2. Sponges are basal animals 3. ( true animals ) is a clade of animals with true tissues 4. Most animal phyla belong to the clade Bilateria 5. There are three major clades of bilaterian animals, all of which are invertebrates, animals that lack a backbone, except Chordata, which are classified as vertebrates because they have a backbone 59 Figure 32.11 ANCESTRAL PROTIST 770 million 680 million Bilateria 670 million Lophotrochozoa Ecdysozoa Hemichordata Chordata Rotifera Ectoprocta Brachiopoda 60 Figure 32.11a Figure 32.11b ANCESTRAL PROTIST 770 million 680 million Bilateria 670 million 61 Lophotrochozoa Ecdysozoa Hemichordata Chordata Rotifera Ectoprocta Brachiopoda 62! The bilaterians are divided into three clades:, Ecdysozoa, and Lophotrochozoa! includes hemichordates (acorn worms), echinoderms (sea stars and relatives), and chordates! This clade includes both vertebrates and invertebrates 63! Ecdysozoa is a clade of invertebrates that shed their exoskeletons through a process called ecdysis 64

Figure 32.12 Figure 32.12a Future Directions in Animal Systematics! Lophotrochozoa is another clade of bilaterian invertebrates Lophophore Apical tuft of cilia Lophophore! Systematics, like all fields of scientific research, is an ongoing, dynamic process of inquiry! Some lophotrochozoans have a feeding structure called a lophophore! Three outstanding questions are the focus of current research! Others go through a distinct developmental called the trochophore larva (a) Lophophore feeding structures of an ectoproct (b) Structure of a trochophore larva (a) Lophophore feeding structures of an ectoproct 1. Are sponges monophyletic? 2. Are ctenophores basal metazoans? 3. Are acoelomate flatworms basal bilaterians? 65 66 67 68 Figure 32.UN01 Figure 32.UN02 Figure 32.UN03 Figure 32.UN04 Animal Phylum Cephalochordata Urochordata Vertebrata No. of i mirnas (x i) 1 5.8 2 35 3 2.5 4 26 5 38.6 6 33 7 59.1 8 25 9 50.8 10 58 11 147.5 S x No. of Cell Types (y i) 25 30 34 38 45 68 73 77 83 94 172.5 S y 535 525 mya: Cambrian explosion 560 mya: Ediacaran animals Era 365 mya: Early land animals Origin and diversification of dinosaurs Diversification of mammals Neoproterozoic Paleozoic Mesozoic Cenozoic 1,000 542 251 65.5 0 Millions of (mya) True tissues Bilateral symmetry Three germ layers (basal animals) (basal bilaterians) Lophotrochozoa Ecdysozoa Bilateria (most animals) Blastopore Fate Protostomy (P) Deuterostomy (D) Neither (N) Phyla, Rotifera, ; most, most ; few, Chordata; most ; few, few Source: A. Hejnol and M. Martindale, The mouth, the anus, and the blastopore open questions about questionable openings. In Animal Evolution: Genomes, Fossils and Trees, eds. D. T. J. Littlewood and M. J. Telford, Oxford University Press, pp. 33 40 (2009). 69 70 71 72 Figure 32.UN05 73