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One form is the jelly-fish or umbrella shape — called medusa, and the
other is a tubular form called polype. There are three classes.
The Hydrozoa include animals with the polype as the predominant form,
although there might be an alternation of generations involving a medusa
stage. Most of them are marine, and most are colonial. Most of the
Hydrozoa arc small in size and form branched colonies encrusted on
stones, etc.; there are, however, some pelagic forms which swim by means
of a float. The characteristic means of defence is by nematocysts which, in
some animals,, like the Portuguese Man-of-war, may be deadly. In the
pelagic forms, the different polypes assume different roles, such as
flotation, defence, digestion, and reproduction.
In tihe Scyphozoa, or jelly-fishes the predominant stage is the swimming
medusa, but there may be an alternation of generations with a temporary
polype-like planula stage.
The Actinozoa include the sea anemones and corals. While the former are
single and lack a skeleton, the latter form colonies and have a hard limy
skeleton. Some, like the sea pens and sea fans, may lack a calcareous
skeleton.
Class Hydrozoa
Order Hydroida
Family Pennaridae
Genus Pennaria Oken
Pennaria distichaGoldfuss
Family Tubulariidae
Genus Tubularia van Beneden
Tubularia crocea(Agassiz)
Phylum COELENTERATA
FAUNA 175