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General Zoology Unit Two Objective Eighteen. Definitions. Diploblastic – having two germ layers from which tissues and structures arise. Ectoderm – outer germ layer that gives rise to tissues and structures that cover the outside.
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Definitions Diploblastic – having two germ layers from which tissues and structures arise Ectoderm – outer germ layer that gives rise to tissues and structures that cover the outside Endoderm – inner germ layer that gives rise to tissues and structures that cover the inside Mesoglea – jelly-like substance found between the inner and outer layers
Gastrulation Ectoderm Mesoderm Endoderm Blastopore Blastula Gastrula Diploblastic
Cnidaria Eukaryotic, eumetazoans Diploblastic Have true tissues, but no organs All are marine Radially symmetrical (no cephalization) Polymorphic – two forms (polyp & medusa) Cnidocytes – stinging cells Have a nerve net Polyps are sessile, while medusae can move Asexual and sexual reproduction
Cnidarian Taxonomy Kingdom - Animalia Phylum - Cnidaria Class – Hydrozoa Ex. – Physalia, Obelia, Hydra, Gonionemus Class – Scyphozoa (true jellyfish) Ex. – Aurelia, Cassiopeia Class – Cubozoa Ex. – Carybdea Class – Anthozoa Ex. – Metridium, Gorgonia, Tubipora
Class - Hydrozoa Most are marine and colonial in form Most forms exhibit alternation of generations between asexual polyps and sexual medusae, but some have only one or the other form Obelia Hydra Physalia
Class - Scyphozoa Referred to a the true jellyfish All are solitary Polyp stage is much reduced or absent Main body is cup shaped Aurelia
Class - Cubozoa All are relatively small in size All are solitary Polyp stage is much reduced Main body is cube shaped Carybdea
Class - Anthozoa Polyp form predominant, no medusa stage Some are solitary, while others are colonial Many form zooxanthellae relationship with algae Most ecologically important group due to reef building Metridium Gorgonia Tubipora
Alternation of generations Planula Budding
Alternation of generations Planula Budding