Phylum Cnidaria

Phylum Cnidaria

• Include Hydras, jellyfish, sea anemones & corals
• Radially symmetrical
• Acoelomate
• Two basic forms:

1. Polyp: Cylindrical form which attach bases to substratum
2. Medusa: Flattened, mouth down version of the polyp. Moves freely

Basic Body Plan:

• Has an outer epidermis
• Has an inner gastrodermis which forms a gastrovascular cavity
• Has a middle "jelly filled" layer called mesoglea

Cnidarian Body plans

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• Cnidarians are predators which have tentacles possessing batteries of special cells called Cnidocytes
• Cnidocytes contain special stining capsules called nematocysts.
  • When triggered, these cells shoot out a discharge thread which can entangle and/or poison it's intended prey

Reproduction

• Reproduction can occur sexually by fertilization of egg and sperm forming larvae.
• Reproduction can also occur asexually through budding

3 Major classes

1. Class Hydrozoa: Hydras
2. Class Scyphozoa: Jellyfish
3. Class Anthozoa: Anemones and corals

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