Phylum Cnidaria

Phylum Cnidaria – “stinging cell” A.k.a Coelenterata (hollow cavity) Radiata (radial symmetry)

Jelly Fishes

Sea Anemones

Corals

One step above sponges… Differ from sponges - have rudimentary organs Incomplete digestive & excretory systems No blood or circulatory system

Classification 3 Classes Hydrozoa = Hydra Scyphozoa = Jellyfish Anthozoa = Sea anemones & coral

Morphology Body wall - 3 layers Epidermis (outside) Mesoglea (inner transluscent jelly-like material) Gastrodermis (inside lining)

Skeletal Structure Corals secrete calcium carbonate to build exoskeleton Most sea anemones and hydra use water pressure from inside body cavity (hydrostatic pressure) to maintain body form

Body Features Mouth usually surrounded by tentacles (radial symmetry) Tentacles covered in cnidocytes = specialized stinging cells Nematocysts = Shoots like a harpoon from cnidocyte. Contains deadly toxin. Gastrovascular cavity – Hollow digestive cavity Mouth serves as entrance/exit point

Nervous System No brain Nerve net Capable of responding to stimuli

Habitat Aquatic, mostly marine Hydra – Freshwater, independent, free swimming Jellyfish – Marine, independent, free swimming Coral & Anemone – Marine, sessile, colonial

Body Forms Polyp – present in all 3 classes Hollow tube with tentacles Can be free swimming (hydrozoa, scyphozoa) or sessile (anthozoa)

Body Forms Medusa – only present in hydrozoa and scyphozoa Free swimming Umbrella shaped with tentacles Mesoglea constitutes bulk

Reproduction Hydrozoa & Scyphozoa – Anthozoa – Asexual reproduction in polyp form by budding Sexual reproduction in medusa form Anthozoa – No medusa form, but can reproduce asexually (budding) or sexually

Close-up of Hydrozaon polyp

Hydrozoan medusa