INTRO TO ANIMAL DIVERSITY Common Characteristics Development History Body Plan Diversity and Phylogeny

Common Characteristics of Animals: multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers Cell Structure Multicellular, Eukaryotic, no cell walls Support by extracellular proteins (e.g., collagen, cadherins) Most have Muscle & Nervous tissues Nutritional Mode: Heterotrophs w/ internal digestion REPRODUCTION/LIFE-CYCLE Mostly sexual reproduction & diploid dominant DEVELOPEMENT Zygote  cleavage  gastrulation & tissue (germ layer) formation Regulated by homeoboxes (e.g., Hox genes

Eight-cell stage Cross section of blastula Cross section of gastrula Figure 32.2-3 Zygote Cleavage Eight-cell stage Cleavage Blastocoel Cross section of blastula Blastula Figure 32.2-3 Early embryonic development in animals (step 3) Gastrulation Cross section of gastrula Blastocoel Endoderm Ectoderm Blastopore Archenteron

Larval Stages Most animals have at least one larval stage Morphologically distinct from parent; different food source (ecological role) Larvae juvenile A juvenile resembles an adult, but is not yet sexually mature metamorphosis

Evolutionary History of Animals: 770-700 m. y. of evolultion; 1 Evolutionary History of Animals: 770-700 m.y. of evolultion; 1.3+ million species Fossil evidence of animals 770 m.y.o Closest living relative to animals are Choanoflagellates Cadherin protein domain similarities Cell attachement and cell signalling gene similarity + morphological similarity w/ sponges CCD domain that is unique to animals 560 m.y.a.: macroscopic animals & predator-prey relationships 535-525 m.y.a: Cambrian explosion large animals, bilateral animals, exoskeletons, mineralized endoskeletons inc. arthropods, chordates, and echniderms ~450 m.y.a .: first terrestrial animals appear (arthropods) ~365 m.y.a.: first terrestrial vertebrates appear giving rise to reptiles and amphibians ~ 251-65 m.y.a.: first mammals appear (coincides with angiosperm development) 65m.ya.- present: Large marine reptiles and non-flying dinosaurs experienced massive extinctions, medium and large mammals came to dominate terrestrial ecosystems

Individual choanoflagellate Choano- flagellates OTHER EUKARYOTES Figure 32.3 Individual choanoflagellate Closest animal relative Choano- flagellates OTHER EUKARYOTES Sponges Figure 32.3 Three lines of evidence that choanoflagellates are closely related to animals Animals Collar cell (choanocyte) Other animals

Choano- flagellate Hydra “CCD” domain (only found in animals) Fruit Figure 32.4 Choano- flagellate Hydra “CCD” domain (only found in animals) Fruit fly By recombination of choanoflagellate domain + unique domain Mouse Figure 32.4 Cadherin proteins in choanoflagellates and animals

Animals can be characterized by “body plans” Body plan = symmetry + tissue organization + body cavity + development Asymmetry Radial symmetry Bilateral symmetry Germ Layers: Endoderm? Ectoderm? Mesoderm? aceolomate psuedocoelomate coelomate Protostome dueterostome

Bilaterally symmetric Symmetry Bilaterally symmetric Radially symmetric asymmetric

(a) Radial symmetry (b) Bilateral symmetry Figure 32.8 Figure 32.8 Body symmetry (b) Bilateral symmetry

Video: Sea Urchin Embryonic Development (Time Lapse)

Coelomates & pseudocoelomates = grades NOT clades Body Cavity = Coelum (a) Coelomate (b) Psuedocoelomate Coelom Body covering (from ectoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Muscle layer (from mesoderm) Pseudo- coelom Digestive tract (from endoderm) Digestive tract (from endoderm) (c) Acoelomate Body covering (from ectoderm) Key Ectoderm Figure 32.9 Body cavities of triploblastic animals Tissue- filled region (from mesoderm) Mesoderm Endoderm Wall of digestive cavity (from endoderm) Coelomates & pseudocoelomates = grades NOT clades

(a) Coelomate Coelom Body covering (from ectoderm) Tissue layer Figure 32.9a (a) Coelomate Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Figure 32.9a Body cavities of triploblastic animals (part 1: coelomate) Key Ectoderm Mesoderm Endoderm

(b) Pseudocoelomate Body covering (from ectoderm) Muscle layer (from Figure 32.9b (b) Pseudocoelomate Body covering (from ectoderm) Muscle layer (from mesoderm) Pseudo- coelom Digestive tract (from endoderm) Figure 32.9b Body cavities of triploblastic animals (part 2: pseudocoelomate) Key Ectoderm Mesoderm Endoderm

Wall of digestive cavity (from endoderm) Figure 32.9c (c) Acoelomate Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) Figure 32.9c Body cavities of triploblastic animals (part 3: acoelomate) Key Ectoderm Mesoderm Endoderm

Protostome development (examples: molluscs, annelids) Figure 32.10 Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (a) Cleavage Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate (b) Coelom formation Coelom Archenteron Coelom Mesoderm Blastopore Blastopore Mesoderm Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. Figure 32.10 A comparison of protostome and deuterostome development (c) Fate of the blastopore Anus Mouth Digestive tube Key Ectoderm Mesoderm Mouth Anus Endoderm Mouth develops from blastopore. Anus develops from blastopore.

Protostome development (examples: molluscs, annelids) Figure 32.10a Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (a) Eight-cell stage Eight-cell stage Cleavage Figure 32.10a A comparison of protostome and deuterostome development (part 1: cleavage) Spiral and determinate Radial and indeterminate

Protostome development (examples: molluscs, annelids) Figure 32.10b Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (b) Coelom formation Coelom Archenteron Coelom Key Mesoderm Blastopore Blastopore Mesoderm Ectoderm Figure 32.10b A comparison of protostome and deuterostome development (part 2: coelom formation) Mesoderm Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. Endoderm

Protostome development (examples: molluscs, annelids) Figure 32.10c Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (c) Fate of the blastopore Anus Mouth Digestive tube Key Ectoderm Mouth Anus Figure 32.10c A comparison of protostome and deuterostome development (part 3: fate of the blastopore) Mesoderm Mouth develops from blastopore. Anus develops from blastopore. Endoderm

Cleavage In protostome development, cleavage is spiral and determinate In deuterostome development, cleavage is radial and indeterminate With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo Indeterminate cleavage makes possible identical twins, and embryonic stem cells

Coelom Formation 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

Fate of the Blastopore 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

36+ animal phyla: based on morphological, molecular, and fossil data 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. Eumetazoa (“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

invertebrates protostomes Porifera Metazoa Ctenophora ANCESTRAL Figure 32.11 Porifera ANCESTRAL PROTIST Ctenophora Metazoa Cnidaria Eumetazoa Acoela Single common animal ancestor Hemichordata Echinodermata True Tissues Deuterostomia Bilateria Chordata Bilateral & 3 germ layers Platyhelminthes invertebrates Rotifera Only phylum containing vertebrates Ectoprocta Figure 32.11 A phylogeny of living animals Lophotrochozoa Brachiopoda protostomes Mollusca Annelida Nematoda Ecdysozoa Arthropoda