Ch. 32 An Overview of Animal Diversity

Animals

Heterotrophs, ingest food, multicellular, cells supported by structural proteins

Cleavagelarva

After a sperm fertilizes an egg, the zygote undergoes rapid cell division and leads to multicellular, hollow blastula

• then gastrulation to form gastrula

larva

sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis to become juvenile (not sexually mature)

Hox genes

regulate the development of body form and can produce a wide range of animal morphology

History of Animals

~1.9 million living species

• common ancestor resembled modern choanoflagellates + around 770 MYA

• Multicellularity requires adhere + signal

Neoproterozoic Era (1 BYA - 541 MYA)

Early members of the animal fossil record include the Ediacaran biota (635-541 MYA)

• fossils of embryos + predation found in rocks

Paleozoic Era (541-252 MYA)

The Cambrian explosion (535–525 MYA) marks the earliest fossil (bilaterians) appearance of many major groups of living animals

• Traits: bilateral sym, complete digest tract, one-way digest system

Causes of Cambrian explosion and Edicaran biota decline (3)

• Animals on land (450 MYA)

• Vertebrates on land (365 MYA)

1. New predator-prey relationships

2. A rise in atmospheric oxygen

3. The evolution of the Hox gene complex and addition of new microRNAs

Mesozoic Era (252-66 MYA)

Coral reefs emerged, plesiosaurs reptiles returned to water, dinos, first mammal emerged, flowering plants + insects diversified

Cenozoic Era (66 MYA - Present)

followed mass extinctions of both terrestrial and marine animals

• mammals increase in size + exploited vacated ecological niches

• global climate cooled

Radial Symmetry (Body Plan)

animals have a top and a bottom, but no front and back, or left and right

• sessile or planktonic

Bilateral Symmetry

animals have dorsal (top) and a ventral (bottom), right + left, anterior (front) and posterior (bottom)

• active, CNS, brain

Tissues

collections of 3 germ layer, specialized cells isolated from other tissues by membranous layer

• Ectoderm: cover embryo surface

• Endoderm: innermost germ layer, lines archenteron (digestive tube)

Diploblastic vs Triploblastic

• sponge lacks true tissue

Dip: have only ectoderm + endoderm (onidarians)

Trip: also have mesoderm (bilateral symmetric)

Coelom + functions (2)

True body cavity derived from mesoderm

• Coelomates

1. fluid cushions suspended organs + acts like skeleton against muscles

2. enables organs to grow + move indep of outer body wall

Pseudocoelom

body cavity derived from the mesoderm and endoderm

• pseudocoelomates

Acoelomates

Triploblastic animals that lack a body cavity

Grade

group (not clade) whose members share key biological features

• EX: coelomates + pseudocoelomates have similar body plan

Protostome development

1. Cleavage: spiral + determinate (fate dermined early)

2. Coelom Formation: splitting of solid masses of mesoderm

3. Blastopore: becomes mouth

Deuterostome development

1. Cleavage: radial + indeterminate (can make identical twins + stem cells)

2. Coelom formation: mesoderm buds from wall of archenteron

3. Blastopore: becomes anus

Blastopore

forms during gastrulation and connects the archenteron to the exterior of the gastrula

What are animal phylogenies based on? (5)

1. Whole-genome analysis

2. Morphological traits

3. Ribosomal RNA (rRNA) genes

4. Hox genes

5. Protein-coding nuclear genes & Mitochondrial genes

Relationships among living animals + phylogeny (4)

1. All animals share a common ancestor

2. Sponges are the sister group to all other animals

3. Eumetazoa (“true animals”) is a clade of animals with tissues

4. Most animal phyla belong to clade Bilateria (vertabrates + inv)

Deuterostomia (Bilaterian Clade)

includes hemichordates (acorn worms), echinoderms (sea stars and relatives), and chordates

• vertebrates + invertebrates

Ecdysozoa (Bilaterian Clade)

secrete external skeletons (invertebrates)

• Shed exoskeletons through ecdysis process

Lophotrochozoa (Bilaterian Invertebrate Clade)

Lophophore feeding structure + go through trochophore larva develop stage