The Higher Systematics of Cnidarian Diversity Phylum Cnidaria and Stony Corals Class Hydrozoa (Gr. hydra, water serpent) The Cnidarian Life Cycle • life cycle with both polyps and medusae, although one or the other form may be suppressed (usually polyp-dominant). • gut cavity of polyp is simple, lacking a pharynx and not divided by mesenteries. • tetramerous (four-part) radial symmetry. • medusa stage with a velum (= a narrow shelf of tissue that projects inwards from the margin of the umbrella). • gonads are ectodermal (found in the epidermis). The Hydrozoan • medusa stage may possess specialized balance organs called statocysts and photosensitive organs called ocelli. Life Cycle • solitary or colonials; some colonial forms highly polymorphic. • includes hydroids (“stinging limu”), fire coral, pink coral, adn siphonophores. Hydrozoan Colony Hydrozoan Colonies “Stinging Limu” 1 Hydrozoan Medusa Anatomy of a Hydrozoan Medusa Hydrozoan Medusa Hydrocorals By-the-Wind-Sailor Fire Coral A Floating Colony of Polyps 2 Coloniality Close Up of a Portuguese Man-of-War Phylum Cnidaria Man-Of-War From The World Book (TM) Multimedia Encyclopedia (c) 1999 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved. !"(c) Maira & Rod Borland, Bruce Coleman, Inc.! Class Scyphozoa Scyphozoan Life Cycle (Gr. skyphos, cup) • life cycle with both polyps and medusae, but medusae dominate with polyp stage reduced or absent. • polyp stage (scyphistoma) goes through strobilization to produce young medusa. strobila • bell margin lacks a velum. scyphistoma • tetramerous (= four-part) radial symmetry. ephyra • gut divided into a complex system of radial canals. planula • some with a simple single mouth, but many with thousands of adult medusa microscopic “mouths” at the ends of oral arms. • gonads endodermal (found in the gastrodermis). • specialized sense organs called rhopalia with ocelli & statocysts . gametes • includes some 200 marine species. • "true" sea jellies. Sea Jellies Moon Jelly Anatomy 3 Class Cubozoa (Gr. kybos, a cube) • life cycle with both polyps and medusae, but medusae dominate with polyp stage reduced. Box Jellies • polyp stage develops directly into medusa. • bell margin with a velarium. • tetramerous (= four-part) radial symmetry; bell cube-shaped with tentacles arising from each corner. • gonads endodermal (found in the gastrodermis). • specialized sense organs called rhopalia with ocelli & statocysts . • includes some 15 marine species. • includes box jellies and sea wasps. Box Jelly Anatomy Class Anthozoa (Gr. anthos, flower) • lack medusa stage entirely (polyp forms only) • mouth with a tubular pharynx that projects inward into the gut • large gut cavity divided by mesenteries that radiate inwards from the body wall • gonads endodermal, borne on the mesenteries • hexamerous (6-part) or octamerous (8-part) radial symmetry or biradial (modified radial symmetry that limits the number of planes that can divide the body into equal halves • includes sea anemones, “true” stony corals, sea fans, sea pens, organ pipe coral, precious black coral, & zoanthids Sea Anemone Anatomy Sea Anemones 4 “True” Stony Corals Octocorals 5.