Simple InvertebratesSection 2 Characteristics of Cnidarians Cnidarians have two tissue layers and radial symmetry –Epidermis, –Gastrodermis Mesoglea is the jelly – like substance between the layers. Cnidarians have two basic body forms –Medusa, free floating and are often umbrella shaped –Polyp, tube - like and attach to a rock or some other object
Simple InvertebratesSection 2 Differentiation of Cells Cnidarians have nerve cells arranged into nerve net Sensory cells Muscle - like cells Stinging cells (cnidocytes)
Simple InvertebratesSection 2 Stinging Cells: Cnidocytes Cnidocytes are located on fingerlike tentacles that surround the one opening. Each cnidocyte has a threadlike organelle called a nematocyst –That can contain toxins –Used for defense and to capture prey
Simple InvertebratesSection 2 Reproduction Sexual and asexual reproduction occurs in both forms In Obelia, the life cycle alternates between a polyp and a medusa stage. Once the gametes fuse, a planulae forms as a free- swimming larvae.
Simple InvertebratesSection 2 Groups of Cnidarians The three main groups of cnidarians are; –Class Hydrozoa (Colony, Portuguese man – of – war) –Class Scyphozoa (Common jelly fish) –Class Anthozoa (“flowering” animals, sea anemone)
Simple InvertebratesSection 2 Phylum Ctenophora: Comb Jellies “comb – holder” –8 comb – like rows of cilia Move by beating their cilia Most do not have cnidocytes, instead colloblasts –Secrete sticky substance on two tentacles Apical organ, direction in water Hermaphroditic Bioluminescent