Chapter 32 Introduction to Animal Diversity

Animal Characteristics 1.) All are heterotrophs & must ingest food to digest it. 2.) All eukaryotic and multicellular. 3.) Cell do NOT have cell walls. 4.) Cells are held together by structural proteins (such as collagen).

Animal Characteristics 5.) Have muscle & nerve cells. 6.) Most reproduce sexually. a.) Diploid zygote usually undergoes cleavage: cell divisions without cell growth. b.) Cleavage leads to formation of a hollow ball of cells called a blastula. c.) Blastula undergoes gastrulation: formation of embryonic tissue layers that will develop into adult parts. i.) Results in a stage called a gastrula. (Unique to animals).

Animal Characteristics 7.) All animals have genes called Hox genes that play large roles in development. a.) Control cell differentiation & division producing morphological (body shape) features.

Animal Evolution 1.) Ancestor of animals (& fungi) was most likely a flagellated protist. 2.) First fossils that are clearly animals are from 575 mya. 3.) Animal diversification occurred widely during the Cambrian period – “Cambrian explosion.”

Animal Body Plans 1.) Symmetry a.) No body symmetry: sponges b.) Radial symmetry: symmetry around a central point (no left or right side) - sea anemones c.) Bilateral symmetry: two-sided symmetry with a left & right side

Animal Body Plans i.) Animals with bilateral symmetry typically have their sensory organs concentrated at one end (the head end). This trend is called cephalization. ii.) Symmetry fits lifestyle: radial animals are generally sessile (don’t move) & sensory organs are not concentrated at any “end.” Bilateral animals typically move – head end (with sensory organs) first.

Animal Body Plans 2.) Tissues: collections of specialized cells isolated from other tissues by membranous layers. a.) Sponges are the only animals without true tissues.

Animal Body Plans b.) In all other animals, tissue layers form during gastrulation. These embryonic tissue layers are called germ layers: i.) Ectoderm: outer layer - gives rise to outer covering of animal & (in some) CNS. ii.) Endoderm: inner layer – lines developing digestive tract (called archenteron) & gives rise to lining of digestive tract & organs derived from it (liver & lungs). iii.) Mesoderm: middle layer – forms muscles & most other organs.

Animal Body Plans c.) Diploblastic animals: have only endo- and ectoderm (jellyfish & corals). d.) Triploblastic animals: have all 3 germ layers (vertebrates, arthropods, flatworms)

Animal Body Plans 3.) Body cavities: fluid-filled space separating the digestive tract from outer body wall – also called a coelom. a.) A “true” coelom is derived from the mesoderm. Animals with this are called coelomates.

Animal Body Plans b.) Pseudocoelomates have a coelom but it is not derived from mesoderm.

Animal Body Plans c.) Acoelomates do not have a coelom.

Animal Body Plans d.) Functions of body cavity: i.) Fluid cushions organs. ii.) Space allows organs to grow & move independently.

Animal Body Plans 4.) Protostome vs. Deuterostome Development a.) Protostomes (molluscs, annelids, arthropods): i.) Spiral cleavage pattern in embryos ii.) Determinate cleavage: “fate” of cells is determined very early. iii.) Coelom formation is schizocoelous: solid masses of mesoderm split to form coelom. iv.) Blastopore (indentation that form digestive tube) eventually forms mouth.

Animal Body Plans b.) Deuterostomes (echinoderms, chordates): i.) Radial cleavage pattern ii.) Indeterminate cleavage iii.) Coelom formation is enterocoelous iv.) Blastopore becomes anus

Animal Phylogeny There is some disagreement (due to new evidence) over some of the divisions in the animal phylogenetic tree/cladogram. However, some points are agreed upon… 1.) All animals share a common ancestor 2.) Sponges (phylum Porifera) diverged from other animals & are called parazoans – they are the ONLY animals without true tissues.

Animal Phylogeny 3.) All other animals are in a group called the eumetozoans – they have true tissues. 4.) Eumetozoans are divided by their body symmetry into: a.) Radiata: those with radial symmetry b.) Bilateria: those with bilateral symmetry

Animal Phylogeny 5.) Bilateria is subdivided (traditionally) into: a.) Deuterostomes: Vertebrates (phylum Chordata), echinoderms & some other phyla. b.) Protostomes: arthropods, worms, molluscs c.) This division is under the most debate – molecular evidence is now showing that some different divisions might be more appropriate (see pages 634 & 635). d.) Protostomes are often subdivided further.