REN R205 Lecture Notes - Lecture 14: Cryptobiosis, Tardigrade, Hermaphrodite
7 Apr 2016
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Document Summary
Simple, without internal nervous, digestive, or circulatory systems, fairly unique in their asymmetry. Unspecialized cells change from 1 type to another. Pump water through pores, filtering food from water. Most are marine, some live in freshwater streams, ponds and lakes. Freshwater ones are small, greenish, since algae live symbiotically in them (endosymbiosis) 2 body types in life cycle: medusa (jelly-fish like), polyp (anemone) In eastern canada and usa, there is freshwater medusa. Use stinging cells to kill prey (called cnidocytes, cnidoblasts, nematocytes) Hydras are simple in construction, without internal organs. Non segmented worms that are more or less rounded in cross section. Important in soil fauna, freshwater ecosystem, as parasites and as economic pests. Majority are parasitic, immense diversity of ecological roles, not physical appearance. Said if all nematodes were gone our world would be dimly recognizable. Bilaterians clade bilateria: bilaterally symmetrical, free living or parasitic many are important internal parasites of vertebrates.
