BIOL 111 Lecture 8: Lecture 8 Cnidarians and Platyhelminthes

• School: McGill University
• Department: Biology
• Course: BIOL 111
• Professor: Andrew Hendry

Document Summary

Not self induced, caused by waves or predators. Covered in thicc membrane, once ready it"ll land and grow. Jellyfish, sea anemones, coral, hydrozoans are all cnidarians. Large and small species, 11000 species, micro and macroscopic. Epidermis from ectoderm, mesoglea collagen and proteoglycans, gastrodermis from endoderm, mouth/anus from blastopore. Most life cycles include both polyp and medusa. Polyp is sessile, asexual reproduction, medusa is motile, sexual reproduction. Polyps bud to medusa, medusa produces haploid gametes. Cnidarians are mostly carnivorous, use extracellular digestion in gastrovascular cavity. Corals use symbiotis with algae, which provide 80% of their energy (dinoflagellates) On it is the nematocyst, a spear-like barbed structure full of toxins. Nerve net, sensory information comes from any direction. Strong nematocysts felt by and harmful to humans. Tolerates low o2 levels due to symbiosis. Can kill humans, kill more humans per year than sharks. Anemone fish and shrimp can touch anthozoa without getting stabbed by cnidocytes.