Spiny polyp

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Spiny polyp
Hydractinia echinata, female colony (from Allman, 1872) .png

Spiny polyp ( Hydractinia echinata )

Systematics
Class : Hydrozoa (Hydrozoa)
Order : Anthomedusae
Subordination : Filifera
Family : Hydractiniidae
Genre : Hydractinia
Type : Spiny polyp
Scientific name
Hydractinia echinata
Fleming , 1823

The spiny polyp (also hydroid polyp ) ( Hydractinia echinata ) from the tribe of Cnidaria lives in the North Sea and in the northern part of the Atlantic on snail shells of the genus Buccinum (= whelk ) and Littorina (= periwinkle ). The snail shells are in turn inhabited by hermit crabs of the genus Pagurus . In the presence of a crab, the hydractinia are mobile and also benefit from its food remains.

Spiny ploypes on a shell of the whelk ( Buccinum undatum )

The polyp hives are of separate sexes, so that a snail shell is almost always inhabited by only one male or female animal hive (unless it has been colonized by two or more primary polyps in different places at the same time). Hydractinia echinata shows a morphological and functional differentiation of the individual polyps (= polymorphism ), which are connected to one another via a network of stolons . The tentacle-bearing nutrient polyps (gastrozooids) are used to catch prey. These nutritional polyps have a mouth opening and supply nutrients to the entire canal through the gastrovascular system . Defense polyps (spiral oozoids, tentaculozooids) serve to protect the stick. Another form of polyps are the sexual polyps (gonozooids). They are responsible for the production of sex products (opaque sperm and reddish, isolecital eggs ). Under certain conditions (e.g. light stimulus), these germ cells are released into the open water, where fertilization takes place and a free-swimming planula larva develops. This finally attaches itself to a suitable place and forms a primary polyp, which in turn is the starting point for a new stick. Responsible for the German name "Stachelpolyp" is the stolon plate, which consists of chitin and periderm and forms partially calcified spines, which probably also serve to protect the stick.

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