6 Animal Diversity

What are the overall traits that link all animals together?

Multicellular, heterotrophic, lack cell walls, specialized tissues (except sponges), motile at some life stage, reproduce sexually (mostly), develop from a blastula.

What are choanoflagellates? How are they related to animals?

Single-celled or colonial protists with a collar-like flagellum; closest living relatives of animals; sponges’ choanocytes resemble them.

How do sponges fit the basic criteria for animals?

Multicellular, heterotrophic, reproduce sexually/asexually, motile larval stage, specialized cells (choanocytes).

What morphological and developmental features are used to classify animals?

Symmetry, tissue layers, body cavity (coelom), segmentation, embryonic development (protostome/deuterostome), appendages, and nervous system organization.

What are the different types of symmetry? Examples?

• Asymmetry: No symmetry (sponges).

• Radial symmetry: Symmetry around a central axis (cnidarians, adult echinoderms).

• Bilateral symmetry: One plane divides organism into mirror images (most animals, humans, arthropods).

What is cephalization? Why is it important?

Concentration of sensory and nervous tissues at the anterior end (head); benefits: better coordination, sensing environment, hunting/avoiding predators.

How do animals use segmentation?

Division into repeated units; allows specialization of segments → diverse appendages and functions (e.g., arthropod legs, vertebrate vertebrae).

Define gastrulation. What are the germ layers? How are germ layers used to classify animals?

Embryonic process forming germ layers from blastula.

Ectoderm: Skin nervous system Mesoderm: muscle circulatory system Endoderm: gut organs

• Diploblastic: 2 layers (ectoderm, endoderm) – cnidarians

• Triploblastic: 3 layers – most other animals

Define protostome vs. deuterostome.

• Protostome: blastopore → mouth (e.g., mollusks, annelids, arthropods)

• Deuterostome: blastopore → anus (e.g., echinoderms, chordates)

Coelomate, acoelomate, pseudocoelomate?

• Coelomate: true body cavity lined with mesoderm (annelids, mollusks, vertebrates)

• Pseudocoelomate: cavity partially lined with mesoderm (nematodes)

• Acoelomate: no body cavity (flatworms)

What was the Cambrian "explosion"?

Rapid diversification of animal phyla ~540 mya; appearance of most major body plans.

Defining characteristics of cnidarians?

Radial symmetry, diploblastic, gastrovascular cavity, cnidocytes (stinging cells), polyp/medusa forms.

How are all bilaterians defined?

Triploblastic with bilateral symmetry; classified into protostomes and deuterostomes based on gastrulation.

What are annelids? Examples?

Segmented worms; coelomates; examples: earthworms, leeches; related to mollusks and other lophotrochozoans.

What are mollusks? Characteristics and examples?

Coelomates, protostomes, soft-bodied, usually have a mantle and muscular foot.

• Gastropods: snails/slugs – spiral shell, foot for crawling

• Cephalopods: squid/octopus – tentacles, advanced eyes

• Bivalves: clams/oysters – two shells, filter feeders

Nematodes?

Roundworms, pseudocoelomates, molting cuticle, related to arthropods; free-living or parasitic.

Arthropods?

Segmented, jointed appendages, exoskeleton, open circulatory system; most diverse animal group.

Four major arthropod groups?

• Chelicerates: spiders, scorpions – 2 body segments, 8 legs

• Myriapods: centipedes, millipedes – many legs

• Crustaceans: crabs, lobsters – 2 pairs antennae

• Hexapods: insects – 6 legs, wings

Define metamorphosis

Transformation from juvenile to adult form (e.g., caterpillar → butterfly).

Vertebrates as deuterostomes?

All vertebrates are deuterostomes because blastopore → anus; not all deuterostomes are vertebrates (echinoderms).

Echinoderm characteristics?

Radial symmetry (adult), water vascular system, endoskeleton; more closely related to vertebrates due to development and coelom.

Difference between chordates and vertebrates? Craniates?

Chordates have notochord, dorsal nerve cord, pharyngeal slits, post-anal tail; vertebrates are chordates with a backbone.

Chordates with skulls; includes all vertebrates.

Why aren’t "fish" monophyletic?

Fish” includes jawless fish, cartilaginous fish, and bony fish; they don’t include all descendants (like tetrapods).

Amphibians? Amniotes? Adaptations?

Double life” – aquatic larvae (gills), terrestrial adults (lungs, limbs); moist skin.

Amniotic egg, waterproof skin, thoracic breathing; reptiles, birds, mammals.

Q: Bird evolution?

Evolved from theropod dinosaurs.

Mammals vs. reptiles? Egg-laying mammals?

Mammals: hair, mammary glands, endothermic, differentiated teeth; reptiles: scales, mostly ectothermic, lay eggs.

Monotremes (platypus, echidnas); lay eggs but have mammary glands.

Marsupials vs. placentals?

• Marsupials: short gestation, young develop in pouch (kangaroo)

• Placentals: long gestation, placenta nourishes fetus (humans, whales)