Phylum Cnidarians Include Hydras jellyfish sea anemones corals

Phylum Cnidarians Include Hydras, jellyfish, sea anemones & corals Radially symmetrical Acoelomate Two basic forms: –Polyp: Cylindrical form which attach bases to substratum –Medusa: Flattened, mouth down version of the polyp. Moves freely

Acoelomate

Forms of Cnidarians

Body Plan Basic Body Plan: Has an outer epidermis Has an inner gastrodermis which forms a gastrovascular cavity Has a middle "jelly filled" layer called mesoglea

Cnidocytes Cnidarians are predators which have tentacles possessing special cells called Cnidocytes contain special stinging capsules called nematocysts. When triggered, these cells shoot out a discharge thread which can entangle and/or poison it's intended prey

Reproduction – Reproduction can occur sexually by fertilization of egg and sperm forming larvae. – Reproduction can also occur asexually through budding 3 Major classes – Class Hydrozoa: Hydras – Class Scyphozoa: Jellyfish – Class Anthozoa: Anemones and corals

Class Hydrozoa: The Hydras Polyp phase is dominant Generally microscopic Generally freshwater

Class Scyphozoa: The Jellies Generally refered tro as jellies Medusa stage is dominant Come in a variety of forms Aggressive predators, and can be dangerous to humans Jelly Portugese Man-o-war

Class Anthozoa: Anemones & Corals Appear like plants but are animals. Polyp form is dominant. Corals build calcium shells to protect themselves Anemone – Have symbiotic relationship with algae. Can build extensive masses which can form land masses. Coral Polyps