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Cnidarians. Ms. Moore 2 /5/13. What is a Cnidarian?. The phylum Cnidaria includes: hydras, jellyfish, sea anemones, and coral. Cnidarian = soft bodied, carnivorous animals that have stinging cells arranged in a circle around their mouth.
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Cnidarians Ms. Moore 2/5/13
What is a Cnidarian? • The phylum Cnidaria includes: hydras, jellyfish, sea anemones, and coral. • Cnidarian = soft bodied, carnivorous animals that have stinging cells arranged in a circle around their mouth. • They are the simplest animals to have body symmetry and specialized cells. • Cnidocytes: stinging cells located along their tentacles • Nematocyst: poison-filled, stinging structure with dart
Form and Function • Body Plan = radially symmetrical, central mouth surrounded by many tentacles • 2 Stage Life Cycle • Polyp: cylindrical body with arm-like tentacles; sessile; mouth pointing upward • Medusa: motile body with mouth pointing downward • Both stages have internal space called gastrovascular cavity, this is where digestion occurs
Feeding = after paralyzing their prey, Cnidaria pulls it into its gastrovascular cavity • Digestion starts outside cells in the gastrovascular cavity and finishes inside. Anything indigestible is pass out the mouth. • Respiration, Circulation, and Excretion • Cnidarians respire and eliminate wasted by diffusion through body walls • Response = nerve net that is spread throughout their body and allows detection of stimuli • Statocysts: detect direction of gravity • Ocelli: detect light with eyespots
Movement = various • Hydrostatic skeleton: layer of circular muscles and a layer of longitudinal muscles that use water of GV cavity to move • EX: jellyfish move by jet propulsion • Reproduction = sexual & asexual • Polyp: budding (asexual) to make identical offspring or tiny medusas that grow into adult • External fertilization: sperm and egg unite in water outside body; zygote grows into larva; attach to surface and develop into embryo
Groups of Cnidarians • Jellyfishes: can be 4m in diameter and the tentacles can get up to 30m long; reproduce sexually • Class: Scyphozoa, “cup animals” • Hydras & relatives: most common body form is polyp; get energy from stinging and digesting small prey or symbiotic relationships; produce sexually or asexually • Class: Hydrozoa • Sea Anemones & Corals: have only polyp stage; reef can be several various forms; central body with many tentacles; Anemones live at all depths; use nematocyst to catch prey; repreduce sexually or asexually; grow colonial (with others) and secrete calcium carbonate (limestone) • Class: Anthozoa, “flower animals”
Ecology • Cnidarians distrubution around the world depend on temperature, water depth, and light intensity • Light is used in the symbiotic relationships by photosynthetic organisms = 60% energy • Damaging to corals: logging, farming, bleaching, fertilizer