Chapter 32 An Introduction to Animal Diversity What is an animal? Multicellular, heterotrophic eukaryote – ingestion Structural support from structural proteins – NOT cell walls Nervous tissue & muscle tissue for impulse conduction & movement Sexual reproduction with motile sperm swimming to non-motile egg How did animals evolve? - Current animal development

Figure 32.2 Early embryonic development in animals (layer 1) Zygote Cleavage Eight-cell stage Cleavage – cell division w/out cytokinesis - More cells but same total volume – no cell growth

Figure 32.2 Early embryonic development in animals (layer 2) Zygote Cleavage Eight-cell stage Blastula Cross section of blastula Blastocoel Blastula – hollow ball of cells -coel – opening or cavity

Figure 32.2 Early embryonic development in animals (layer 3) Zygote Cleavage Eight-cell stage Blastula Cross section of blastula Blastocoel Gastrula Gastrulation Endoderm Ectoderm Blastopore Gastrulation – movement of cells to form 2 layers Blastopore – opening where cells move into Ectoderm – outside layer Endoderm – inside layer

Chapter 32 An Introduction to Animal Diversity What is an animal? Multicellular, heterotrophic eukaryote – ingestion Structural support from structural proteins – NOT cell walls Nervous tissue & muscle tissue for impulse conduction & movement Sexual reproduction with motile sperm swimming to non-motile egg How did animals evolve? Current animal development Current hypothesis

Figure 32.4 One hypothesis for the origin of animals from a flagellated protist Colonial protist, an aggregate of identical cells Hollow sphere of unspecialized cells (shown in cross section) Beginning of cell specialization Infolding Gastrula-like “protoanimal” Somatic cells Digestive cavity Reproductive cells

Chapter 32 An Introduction to Animal Diversity What is an animal? How did animals evolve? How are animals grouped & characterized? Body plans Symmetry None (sponge) Radial multiple central axis “cuts” provide mirror images Only have top & bottom Bilateral Only 1 central axis “cut” provides a mirror image Has top, bottom, left & right Radial Bilateral

Chapter 32 An Introduction to Animal Diversity What is an animal? How did animals evolve? How are animals grouped & characterized? Body plans Symmetry & TISSUES None (sponge) Radial multiple central axis “cuts” provide mirror images Only have top & bottom Diploblastic – 2 cell layers Ectoderm Endoderm Bilateral Only 1 central axis cut provides a mirror image Has top, bottom, left & right Triploblastic – 3 cell layers Ectoderm & endoderm Mesoderm – in between ecto- & endoderm Cephalization – movement of sensory equipment towards the anterior end of the organism – associated with movement

Chapter 32 An Introduction to Animal Diversity What is an animal? How did animals evolve? How are animals grouped & characterized? Body plans Symmetry & tissues Body cavities Acoelomates – without a body cavity Pseudocoelomates – “false body cavity” – cavity not completely lined with tissue derived from mesoderm Coelomates – body cavity completely lined with tissue from mesoderm

Figure 32.8 Body plans of triploblastic animals Coelom Body covering (from ectoderm) Digestive tract (from endoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Pseudocoelom Muscle layer (from mesoderm) Tissue- filled region Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm. (a) Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm. (b) Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall. (c)

Chapter 32 An Introduction to Animal Diversity What is an animal? How did animals evolve? How are animals grouped & characterized? Body plans Symmetry & tissues Body cavities Developmental plan Protostome Deuterostome

Figure 32.9 A comparison of protostome and deuterostome development Protostome development (examples: molluscs, annelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Eight-cell stage Spiral and determinate Radial and indeterminate Coelom Archenteron Blastopore Mesoderm Schizocoelous: solid masses of mesoderm split and form coelom Enterocoelous: folds of archenteron form coelom Anus Mouth Mouth develops from blastopore Anus develops Cleavage. In general, protostome development begins with spiral, determinate cleavage. Deuterostome development is characterized by radial, indeterminate cleavage. (a) 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). (b) Fate of the blastopore. In protostome development, the mouth forms from the blastopore. In deuterostome development, the mouth forms from a secondary opening. (c) Digestive tube

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

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

Figure 32.12 Ecdysis Ecdysozoa – secrete an exoskeleton and molt Nematoda & Arthropoda

Figure 32.13 Characteristics of lophotrochozoans 100 m Apical tuft of cilia Mouth Anus (a) An ectoproct, a lophophorate (b) Structure of trochophore larva