(n): (biology) a taxonomic group containing one or more orders
(n): colonial coelenterates having the polyp phase dominant
(n): radially symmetrical animals having saclike bodies with only one opening and tentacles with stinging structures; they occur in polyp and medusa forms
"'I have some delicate specimens of hydrozoa that must be protected—sometimes these seas are perfectly flat ... and sometimes, with no wind or very little, they ... they toss you about in the most extraordinary fashion.'"
--Patrick O'Brian, Blue at the Mizzen, 144