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CNIDARIANS What makes Cnidarians Unique? • Cnidarians are group of animals that are very diverse from stony coral to jellyfish. What common thread keeps this phyla of animals together? Common Thread • Cniadarians are DIPLOBLASTIC (2 Layers – epidermis and gastrodermis) • TRUE TISSUES(muscular, nervous, gastric) • CNIDAE (stinging tentacles) Diploblastic Body • The two tissue layers are the epidermis and the gastrodermis • Mesoglea- Jelly like portion between that separates the two layers. True Tissues • True tissues: muscular, nervous, gastric Cnidae Cnidocytes used in defense, feeding, and attachment Some Cnidocytes can produce Nematocysts or stinging cells Nematocysts Food gathering and defense. Long tube with spines that penetrates prey delivering toxin Nematocysts Two Body Forms • Polyp: tentacle up (anenomes, coral, hydra) • Medusa: tentacle down (jellyfish) Polyp Stage • Sessile, Asexual Reproduction, usually attached to substrate, some “walk” Polyp Stage • Budding • Fission Polyp Stage Polymorphism in polyps Medusa Stage • Dioecious, free swimming, sexual reproduction • Develop reproductive organs (testis and ovaries) Reproduction • Sexual and Asexual reproduction • Alternation of generations Reproduction (sexual) • Egg and Sperm released from GVC • Once combined egg + sperm will form a planula (free swimming larva) • Once GVC devolops forms a Polyp Reproduction (asexual) • Budding • Fission Alteration of Generations • 2 Stages: Polyp & Medusa (dimorphic) • Polyp Stage – some species asexual reproduction by budding, usually sessile Nutrition • Gastrovascular Cavity: Functions in digestion, the exchange of respiratory gases, metabolic waste, and release of gametes Nutrition • Feeding: Prey mostly small crustaceans (copepods) • Nematocysts paralyze prey, contractile cells move prey to mouth, GVC releases enzymes Skeletal System • Hydrostatic – fluid filled body (mesoglea) • Epitheliomuscular cells (longitudinal and circular) Nervous System • Nerve Net – Nervous system is spread throughout entire body • Most primitive nervous system • Some sensory structures – ocelli sense light Circulation, excretion, respiration • No special structures or tissues, these life functions are carried out directly with the environment Hydrozoa • Alteration of generation • Mostly Marine (although a few freshwater) Hydra Obelia Physalia Scyphozoa • • • • True Jellyfish Mostly found in Medusa stage Some harmful some not to humans Ocelli (rhodopalia) allow for Phototaxis (move toward light) Cubozoa • Box Jelly Fish • Some possess dangerous nematocysts • Active swimmers and feeders • Tentacles on corners of medussa Anthozoa • Corals & Anemones • Lack medusa stage Anemones • Can move slowly over some surfaces • Live as individuals but in colonies • Feed on fish and crustaceans or organic debris Corals • Secrete a calcium skeleton • Stony coral, large polyped stony corals, and soft corals • May use symbiotic algae called zooxanthelle for autotrophism. • Can live individually or in groups. Zooxanthelle • Symbiotic Algae that provides food for the coral • Found in reefbuilding coral Soft Coral • No hard calcium skeleton (although may contain fragments inside them) Large Polyped Stony Coral (Octocoral) • Have both soft tissue as well as produces a hard calcium skeleton Stony Corals • Little soft tissue mainly hard calcium skeleton Reef building • Corals can grow on one another to create entire reef systems Issues Affecting Reefs • Many Reef Ecosystems are in peril from being destroyed. • There are many culprits aiding in destruction of the reefs.
