Kingdom Animalia Phylum Cnidaria

Characteristics Radial symmetry Diploblastic organization, 2 official tissue layers Gelatinous Mesoglea Gastrovascular cavity Nerve net Cnidocytes called nematocysts

Coiled nematocyst

Reproduction/Life Cycle Most alternate generations between polyp and medusa form Polyp – asexual, sessile, produce more polyps (colonial) or medusae (pl.) by budding… Medusae – dioecious & free swimming; fertilized larva (Planula) settles & forms a polyp

Cnidarians

Feeding Use nematocysts to stun or kill prey Tentacles bring food to mouth Digested in gastrovascular cavity

Support and Locomotion Hydrostatic Skeleton (supported by water) Polyps – somersault, inchworm, walk on their tentacles… Medusae – swim, use water currents

Classification Class Hydrozoa Most variable class Class Scyphozoa True jellyfish Class Cubozoa Cube jellyfishes Class Anthozoa Largest class

Class Hydrozoa Mostly marine, but only class with freshwater members! Most display alternation of generations, but polyps are dominant form Cnidocytes – only in epidermis Gametes released outside, from epidermis Medusae have a ‘velum’ (shelf-like lip), used for jet propulsion

Hydra Freshwater Polyps only, no medusae

Gonozooid (reproductive zooid) Gastrozooid (feeding zooid) Obelia

Portugese Man-o-War, Physalia Colony of polyps… Cannot swim (floats) Cnidocytes are lethal to small vertebrates and dangerous to humans

Class Scyphozoa “True Jellyfish” – medusa dominant body form Cnidocytes in the epi + gastrodermis Gametes released into gastroderm, then out of mouth Medusae lack a velum

Moon Jellies, Aurelia

Stinging Nettle, Mastigias

Lions Mane, Cyanea Record bell was 7 feet across, 120 ft. tentacles!

Class Cubozoa Medusae are cuboidal Polyps are reduced or absent Tentacles hang from corners Ex. Sea Wasp (type of Box Jellyfish)

Class Anthozoa Polyps only, no medusae Gastrovascular cavity is divided into sections, with mesentaries Sexual and asexual reproduction Sea anenomes, corals, sea fans

Sea Anemones

Corals Sea Fans