Lecture 13 Radiate Animals PDF

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Lecture 13 Radiate Animals Phylum Cnidaria – hydrozoan (hydra), jellyfish, corals and sea anemones Phylum Ctenophora – comb jellies Only animals with true bi-radial (tetramerism = 4 similar parts) symmetry – two planes that create mirror images Cnidaria and Ctenophora are only animal phyla with true biradial symmetry Phylum Echinodermata (starfish) have bilateral larvae, which develop into radially symmetrical adults Phylum Cnidaria  No real organs-tissue level organisation.  Diploblastic: 2-tissue layers-endoderm, ectoderm.  Two body forms-polyp and medusa.  Internal body cavity-gastrovascular cavity.  No respiratory, circulatory, digestive or excretory systems.  Digestion is extracellular in the gastrovascular cavity Characteristics of phylum Cnidaria  Soft-bodied-some have exoskeletons or endoskeletons composed of chitinous, calcareous, or protein components  All predators. Cnidocyte cells containing special stinging organelles called nematocysts, abundant on tentacles, where they may form batteries or rings  Simplest animals with nerve cells-nerve net, no central nervous system/brain  Simplest animals with sense organs-statocysts (up or down, gravity) and ocelli (simple eyes, light)  Muscular system of an outer layer of longitudinal fibres and an inner one of circular fibres  Locomotion by circular contraction, or gliding on basal disc (cilia) Reproduction Asexual reproduction by budding Sexual reproduction-monoecious or dioecious, planula larva. Life cycles often contain both medusa and polyp stages Classes of Cnidarians  Class hydrozoan-Hydra, Portuguese man-o-war  Class Scyphozoa-medium-large ‘true’ jellyfish  Class Cubozoa-box jellyfish, sea wasps  Class Anthozoa-sea anemones, corals Class Hydrozoa  Most hydrozoans are marine and colonial  Usually include both medusa and polyp stage in their life cycle  Examples: hydra, Obelia Class Scyphozoa  True jellyfish  Most range from 2-40 cm in diameter  Medusa dominant stage, polyp stage absent or reduced  Examples: Aurelia, Cyanea Class Cubozoa  Box ‘jellyfish’, most smaller than true jellyfish

 Includes sea wasp (Chironex) of Australia whose stings can kill Class Anthozoa  Means ‘flower animal’ – sea anemones and corals  Polyps only, no medusa stage  All marine  Corals are the only animals which can be seen from space-Great barrier reef Applied Biology  Nematocysts have powerful neurotoxins. Stings can kill or cause discomfort for swimmers, beaches sometimes closed  Coral atolls form pacific islands-therefore they provide habitat for humans too  Great barrier reef and other atolls threatened by discharge of sewage and agricultural fertiliser, pH changes, and pest outbreaks like the thorny starfish Interactions with other animals Certain damselfishes live with sea anemones in the pacific as protection. Unknown property of the skin mucus on fish stops nematocysts firing. Many corals have mutualistic algae (zooxanthellae) living in their tissue. The algae provide food molecules and recycle wastes for corals, which in turn provide shelter. Coral reefs form one of the most diverse ecosystems on the planet-home for many animals. Phylum Ctenophora  Marine, free-swimming animals  Swim using comb rows of cilia  Do not have nematocysts  Luminescence common  Do not form colonies  Similar to Cnidaria in many other respects...