Animal Evolution. Cnidaria. Nematoda. Annelida. Echinodermata. Porifera. Platyhelminthes. Mollusca. Arthropoda. Chordata. sponges. jellyfish. flatworms. roundworms. mollusks. segmented worms. insects spiders. starfish. vertebrates. body & brain size, mobility. backbone.
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digestive & repro sys
distinct body plan; cephalization
specialized structure & function,
muscle & nerve tissue
specialization & body complexity
8 legs, 2 body parts
spiders, ticks, scorpions
gills, 2 pairs antennae
crab, lobster, barnacles, shrimp
6 legs, 3 body parts
Invertebrates:Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata
becomes brain & spinal cord
becomes gills or Eustachian tube
becomes tail or tailbone
Current day hagfishes and lampreys lack hinged jaws – most primitive craniates (chordates with heads)
Why are hagfishes described as craniates rather than vertebrates?
Conclusion: the first tetrapods were not fish with lungs that had gradually evolved legs as the dragged themselves from pool to pool in search of water.
Instead, they were fish with necks and four limbs that raised their heads above water and could breathe oxygen from the air.
yolk sacVertebrates: Reptiles