Cnidarians
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Cnidarians. Ms. Moore 10/12/10. 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

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Cnidarians

Cnidarians

Ms. Moore

10/12/10


What is a cnidarian

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

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


Cnidarians

  • 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


Cnidarians

  • 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

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

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


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