Animal Diversity: Introduction to Body Plans

1. Chapter 32 An Introduction to Animal Diversity “Abridged” version!

2. Overview: Welcome to Your Kingdom • Animal are multicellular • Heterotrophic; must ingest their food • Eukaryotes, with cells lacking cell walls • Tissues that develop from embryonic layers • their bodies are held together by structural proteins such as collagen • Nervous tissue and muscle tissue are unique to animals

3. Single cell Stalk (b) (a) • The common ancestor of living animals • May have lived 1.2 billion–800 million years ago • May have resembled modern choanoflagellates, protists that are the closest living relatives of animals

4. Several characteristics of animals sufficiently define their grouping and levels of complexity • Body plan • Symmetry • Tissues (types, layers) • Body cavities (acoelomate, pseudocoelomate, eucoelomate) • Reproduction and development

5. Concept 32.3: Animals can be characterized by “body plans” • One way in which zoologists categorize the diversity of animals • Is according to general features of morphology and development • A group of animal species • That share the same level of organizational complexity is known as a grade

6. Tissues • 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

7. Animal embryos • Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesoderm • Diploblastic animals • Have two germ layers • Triploblastic animals • Have three germ layers

8. (a) Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images. • Some animals have radial symmetry • Like in a flower pot Figure 32.7a

9. (b) Bilateral symmetry. A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves. • Some animals exhibit bilateral symmetry • Or two-sided symmetry Figure 32.7b

10. Bilaterally symmetrical animals have • A dorsal (top) side and a ventral (bottom) side • A right and left side (lateral) • Anterior (head) and posterior (tail) ends • Cephalization, the development of a head with senses concentrated in one area, is considered an evolutionary step forward

11. Body Cavities • In triploblastic animals • A body cavity may be present or absent

12. (a) Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm. Body covering (from ectoderm) Coelom Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Figure 32.8a • A true body cavity • Is called a coelom and is derived from mesoderm

13. Body covering (from ectoderm) (b) Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm. Muscle layer (from mesoderm) Pseudocoelom Digestive tract (from ectoderm) • A pseudocoelom • Is a body cavity derived from the blastocoel, rather than from mesoderm Figure 32.8b

14. Body covering (from ectoderm) Tissue- filled region (from mesoderm) Digestive tract (from endoderm) (c) Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall. • Organisms without body cavities • Are considered acoelomates Figure 32.8c

15. Reproduction and Development • Most animals reproduce sexually • With the diploid stage usually dominating the life cycle • After a sperm fertilizes an egg • The zygote undergoes cleavage, leading to the formation of a blastula • The blastula undergoes gastrulation • Resulting in the formation of embryonic tissue layers and a gastrula

16. Only one cleavage stage–the eight-cell embryo–is shown here. In most animals, cleavage results in the formation of a multicellular stage called a blastula. The blastula of many animals is a hollow ball of cells. The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage. 2 3 1 Blastocoel Cleavage Cleavage The endoderm of the archenteron de- velops into the tissue lining the animal’s digestive tract. 6 Cross section of blastula Eight-cell stage Blastula Zygote Blastocoel Endoderm The blind pouch formed by gastru- lation, called the archenteron, opens to the outside via the blastopore. 5 Ectoderm Gastrulation Gastrula Blastopore Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer). 4 • Early embryonic development in animals Figure 32.2

17. Digestive cavity Somatic cells Hollow sphere of unspecialized cells (shown in cross section) Reproductive cells Colonial protist, an aggregate of identical cells Beginning of cell specialization Infolding Gastrula-like “protoanimal”

18. Protostome and Deuterostome Development • Based on certain features seen in early development • Many animals can be categorized as having one of two developmental modes: protostome development or deuterostome development

19. Deuterostome development (examples: echinoderms, chordates) Protostome development (examples: molluscs, annelids, arthropods) (a) Cleavage. In general, protostomedevelopment begins with spiral, determinate cleavage.Deuterostome development is characterized by radial, indeterminate cleavage. Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate Cleavage • In protostome development • Cleavage is spiral and determinate • In deuterostome development • Cleavage is radial and indeterminate Figure 32.9a

20. (b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development). Coelom Archenteron Coelom Mesoderm Blastopore Mesoderm Blastopore Enterocoelous: folds of archenteron form coelom Schizocoelous: solid masses of mesoderm split and form coelom Figure 32.9b Coelom Formation • In protostome development • The splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous development • In deuterostome development • Formation of the body cavity is described as enterocoelous development

21. Mouth Anus Digestive tube Anus Mouth Mouth develops from blastopore Anus develops from blastopore Figure 32.9c Fate of the Blastopore • In protostome development • The blastopore becomes the mouth • In deuterostome development • The blastopore becomes the anus

22. Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree • Zoologists currently recognize about 35 animal phyla • The current debate in animal systematics • Has led to the development of two phylogenetic hypotheses, but others exist as well

23. Cnidaria Chordata Mollusca Annelida Rotifera Silicarea Phoronida Nemertea Calcarea Arthropoda Ctenophora Ectoprocta Brachiopoda Nematoda Echinodermata Platyhelminthes “Radiata” Deuterostomia Lophotrochozoa “Porifera” Ecdysozoa Bilateria Eumetazoa Metazoa Ancestral colonial flagellate • One hypothesis of animal phylogeny based mainly on molecular data Figure 32.11

24. Rotifera Cnidaria Porifera Annelida Mollusca Chordata Phoronida Nemertea Ctenophora Nematoda Arthropoda Ectoprocta Brachiopoda Echinodermata Platyhelminthes “Radiata” Deuterostomia Protostomia Bilateria Eumetazoa Metazoa Ancestral colonial flagellate • One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons Figure 32.10