ECON 2010 Lecture 8: Section 8B: Invertebrates
3 Apr 2016
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Mesoglea: gelatinous substance connects the 2 layers. Nerve net: true nerve cells consisting of interconnected neurons with no central control organ. Many have a life cycle that includes both forms. Sessile polyp tubular body with tentacles surrounding opening (mouth and anus) Motile medusa umbrella-shaped body with a mouth on the underside surrounded by tentacles. Figure 31. 3 polyp and medusa forms of cnidarians. Both (a) polyp and (b) medusa forms have two layers of cells, an outer epidermis (from ectoderm) and an inner layer of gastrodermis (from endoderm). In between is a layer of mesoglea, which is thin in polyps, such as corals, and thick in medusae, such as most jellyfish. Named for their unique cnidocytes (stinging cells) Muscles work against fluid in body, act as hydrostatic skeleton. Figure 31. 5 cnidarians have specialized stinging cells called cnidocytes (a) cnidocytes. >100,000 living species, most marine (some freshwater, some terrestrial)
