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You are here: Home1 / Learn2 / Flotsam3 / Corals (and their kins)

Corals (and their kins)

Corals, hydroids, sea anemones and jellyfish all belong to the phylum Cnidaria. Jellyfish represent the free-swimming medusa form, while the others represent the sedentary polyp form. Some cnidarians have both polyp and medusa stages in their life cycle.

Corals are sometimes broken off a reef in storms and washed up. These are the skeletons made by colonies of coral polyps. A coral polyp is like a tiny sea anemone with a limy skeleton surrounding it. Colonies of polyps build up coral reefs with these skeletons. Reef-building corals require high light levels and warm water (over 18C) and have algae living symbiotically inside their tissues.

Fossil Stony Coral

Common name

Fossil stony coral

Scientific name

Goniastrea (Cnidaria: Scleractinia)

Description

The patterns in this coral rock show where the living polyps were. This specimen is probably from the last interglacial period but the genus still exists today.

Hydroids

Common name

Hydroids

Scientific name

(Cnidaria: Hydrozoa: Hydroida)

Description

These delicate structures, often attached to seagrasses, are related to corals and jellyfish. They are colonies of tiny polyps attached to branched stems. Each polyp has a mouth surrounded by tentacles like a tiny sea anemone. Small planktonic animals are caught by stinging cells on the tentacles and eaten.

Cottesloe Coastcare Association

PO Box 32
Cottesloe WA 6911
info@cottesloecoastcare.org

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