sea pen

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sea pen,

long, slender colonial organism of the same phylum as the jellyfish. Sea pen colonies are formed by several genera of the order Pennatulacea. The colony consists of a stalk formed by an organism called a primary polyp (see polyp and medusapolyp and medusa,
names for the two body forms, one nonmotile and one typically free swimming, found in the aquatic invertebrate phylum Cnidaria (the coelenterates). Some animals of this group are always polyps, some are always medusae, and some exhibit both a polyp and a medusa
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) and short branches formed by secondary polyps. The stalk, embedded in sand or mud, holds the colony upright. Sea pens differ from the closely related sea pansiessea pansy,
fleshy, leaf-shaped colony of marine organisms belonging to the genus Renilla in the same phylum as the jellyfish. The colony consists of a stalk formed by a large organism called a primary polyp (see polyp and medusa) that is thrust into soft bottom material;
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 and sea feathers by the form of the colony. Sea pens are marine organisms; they are found on Atlantic and Pacific coasts in shallow to moderately deep water. Some reach a length of 2 ft (61 cm) or more. They belong in the phylum CnidariaCnidaria
or Coelenterata
, phylum of invertebrate animals comprising the sea anemones, corals, jellyfish, and hydroids. Cnidarians are radially symmetrical (see symmetry, biological).
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, class Anthozoa, order Pennatulacea.

sea pen

[′sē ‚pen]
(invertebrate zoology)
The common name for cnidarians constituting the order Pennatulacea.