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• 1) A well defined phylum of about 10,000, mostly marine, predatory species; united by a unique cell type: cnidocyte with nematocyst

  • a) a cnidocyte contains a nematocyst (capsule with an inverted coiled tube & operculum) and a cnidocil (sensory cilium)

  • b) nematocysts come in many forms (grappling, penetrating, sticky)

• 2) Two alternate body forms: medusae (pelagic) & polyp (benthic)

• 3) Exhibit: true tissues (tissue level of organization; epithelial, muscle, nervous), radial symmetry, diploblastic organization

• 4) The basic body plan consists of a body wall (ectoderm, endoderm and mesoglea), hollow tentacles at one end, a mouth (no anus), a gastric cavity with associated canals (=gastrovascular cavity), epithilio-muscular cells, and a nerve net

  --------------- start Friday Jan. 24 -------------

• 5) Cl. Hydrozoa exhibit a bewildering array of life-histories that may emphasize either the polyp or medusa form:

  • a) Hydroids- solitary or colonial polyps predominant (Or. Leptomedusae: polyps thecate, Or. Anthomedusae: polyps naked)

  • b) Hydrocorals- polymorphic polyp colonies with massive skeletons

  • c) Or. Siphonophora- swimming or floating polymorphic colonies

  --------------- start Monday Jan. 27 -------------

• 6) Cl. Scyphozoa (jellyfish), medusa form prominent

• 7) Cl. Athozoa (anemones, corals), medusa form absent

  • a) Hexacorals- heterogeneous group including anemones (Or. Actiniaria) & stony corals (Or. Scleractinia)

  • b) Octocorals- soft corals, gorgonians (Or. Gorgonacea), sea pens (Or. Pennatulacea)

• 8) Asexual reproduction is common; fertilization is mainly external; early cleavage radial; ciliated planula larva forms after gastrulation

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