Evolution & Classification — Animal Phyla & Key Concepts

1.Protostomes: blastopore becomes the mouth first. Spiral cleavage, schizocoely coelom formation. Phyla: Mollusca, Annelida, Arthropoda, plus Platyhelminthes and Nematoda.

2.Deuterostomes: blastopore becomes the anus first; mouth forms later. Radial cleavage, enterocoely. Phyla: Echinodermata and Chordata. Humans are deuterostomes — meaning your anus developed before your mouth in the embryo.

3.Porifera, sponges: asymmetric, no true tissues. Choanocytes drive water flow with flagella; intracellular digestion. Skeleton: spicules of calcium carbonate or silicon dioxide, or spongin protein. Trap: sponges look like plants but are heterotrophic animals that filter feed.

4.Cnidaria: radial symmetry, diploblastic. Key feature is cnidocytes containing nematocysts — stinging cells. Two body forms: polyp like sea anemones, and medusa like jellyfish. Examples: jellyfish, coral, sea anemone.

5.Platyhelminthes, flatworms: bilateral, triploblastic, acoelomate — no body cavity. Flat body, no circulatory or respiratory system, flame cells for excretion. Examples: planaria, tapeworm, fluke.

6.Nematoda, roundworms: bilateral, triploblastic, pseudocoelomate — false body cavity. Cylindrical body, cuticle with molting, complete digestive tract from mouth to anus. Examples: Ascaris, pinworm, C. elegans.

7.Mollusca: bilateral, true coelom, protostome. Key features: mantle, radula (rasping tongue), open circulatory system except in cephalopods. Examples: snail, clam, octopus.

8.Annelida, segmented worms: bilateral, true coelom, protostome. Key features: segmentation, setae or chaetae (bristles), closed circulatory system. Examples: earthworm, leech, polychaete.

9.Arthropoda: bilateral, true coelom, protostome. Key features: chitin exoskeleton, jointed appendages, molting, open circulatory system. Most diverse phylum. Examples: insects, spiders, shrimp and crabs.

10.Echinodermata: larva is bilateral, adult is RADIAL — secondary radial symmetry. True coelom, deuterostome. Key features: calcium carbonate endoskeleton, water vascular system, tube feet. Examples: sea star, sea urchin, sea cucumber.

11.Chordata: bilateral, true coelom, deuterostome. Four chordate features: notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail. Examples: tunicate, lancelet, all vertebrates.

12.Natural selection has four conditions: variation exists in the population; overproduction of offspring; competition for limited resources; differential survival and reproduction based on heritable traits. Result: descent with modification.

13.Endosymbiosis theory: mitochondria and chloroplasts originated from free-living bacteria engulfed by ancestral eukaryotes. Six lines of evidence: double membrane, circular DNA, seventy-S ribosomes (like prokaryotes), binary fission for replication, comparable size to bacteria, ribosomal RNA sequences cluster with bacteria.

14.Allopatric speciation: physical barrier separates populations, they evolve independently, become reproductively isolated. Sympatric speciation: speciation within the same geographic area, often via polyploidy in plants or sexual selection.

15.Reproductive isolation has two types. Prezygotic barriers prevent fertilization — habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation. Postzygotic barriers act after fertilization — reduced hybrid viability, reduced hybrid fertility (mules), hybrid breakdown.