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Kingdom Animalia. Phylum Cnidaria. Characteristics. Radial or biradial symmetry Diploblastic organization Mesoglea between epidermis and gastrodermis Gastrovascular cavity Nerve net Cnidocytes – used in defense and feeding. Reproduction/Life Cycle. Can be monoecious or dioecious
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Kingdom Animalia Phylum Cnidaria
Characteristics • Radial or biradial symmetry • Diploblastic organization • Mesoglea between epidermis and gastrodermis • Gastrovascular cavity • Nerve net • Cnidocytes – used in defense and feeding
Reproduction/Life Cycle • Can be monoecious or dioecious • Alternate generations between polyp and medusa form • Polyp – asexual and sessile • Medusa – dioecious and free swimming
Reproduction Cont’d • Planula – Cnidaria larvae • Polyps are produced by budding or planula • Medusae formed by budding from a polyp body wall
Feeding • Use cnidocytes to stun or kill prey • Tentacles contract to bring food to mouth • Food is digested in gastrovascular cavity
Support and Locomotion • Hydrostatic Skeleton • Some classes have longitudinal muscles that aid in movement • Polyps – somersault, inchworm, glide on base, and walk on their tentacles • Medusae – swim and float
Classification • Class Hydrozoa • Class Scyphozoa • Class Cubozoa • Class Anthozoa
Class Hydrozoa • Mostly marine, but the only class with freshwater members! • Alternate generations • Mostly colonial polyps
Obelia • Gastrozooid – feeding polyp formed from planula larvae • Grows through budding into more gastrozooids • Gonozooid – reproductive polyp that forms medusa by budding • Medusae then reproduce sexually
Gastrozooid Gonozooid
Gonionemus • Medusa predominant • Has a velum (shelf-like lip that projects inward) • Velum creates jet propulsion • Mouth at end of a manubrium • Nerve ring that coordinates swimming movements • Statocyst – responds to gravity
Hydra • Freshwater • Polyps only, no medusae • Testes form sperm by meiosis • Ovaries form one egg each
Physalia • Portuguese man-of-war • Colonial • Cannot swim • Cnidocytes in tentacles are lethal to small vertebrates and dangerous to humans
Class Scyphozoa • All marine • “True Jellyfish” – medusa dominant
Aurelia • Gastrodermal cells have cilia to circulate food • Feeds on plankton • Rhopalia – chemoreceptors • Lappets – touch receptors • Statocysts – gravity sensors • Ocelli - photoreceptors
Class Cubozoa • Medusae are cuboidal • Polyps are reduced or absent • Tentacles hang from corners
Class Anthozoa • Polyps only, no medusae • Mouth has a pharynx • Gastrovascular cavity is divided into sections • Sexual and asexual reproduction