No common name

Hydractinia echinata

ORDER

Filifera

FAMILY

Hydractiniidae

TAXONOMY

Alcyonium echinatum Fleming, 1828, (Scotland, United Kingdom).

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

Hydrorhiza about 0.11 in (3 mm) thick, with numerous blunt conical chitinous spines with jagged edges, encrusting on gastropod shells but also other solid substrata; white to pale pink, giving rise to different kinds of polyps: gastrozooids slender, widening upwards, about eight tentacles in one whorl, hypos-tome conical; gonozooids shorter than gastrozooids, with few tentacles and a ring of gonophores; dactylozooids long, slender.

Medusae reduced to fixed gonophores, sexes generally on different gonozooids; male gonophore yellow to white, ovoid; female gonophore pink and spherical.

DISTRIBUTION

Atlantic, Arctic, and the Mediterranean. (Specific distribution map not available.)

HABITAT

Hydroids grow on gastropod shells inhabited by hermit crabs, on soft bottoms.

BEHAVIOR

Under laboratory conditions, the colonies can be aggressive with the formation of hyperplasic stolons that sting other organisms while competing for the substrate.

FEEDING ECOLOGY AND DIET

Gastrozooids feed on benthic organisms (nematodes, crustaceans, etc.) while being transported by the hermit crab. They also can feed on the larvae of the crab.

REPRODUCTIVE BIOLOGY

Eggs and sperms are released in the water, where fertilization occurs and planulae are formed. Gamete production is almost continuous, but at a slower pace in winter time.

CONSERVATION STATUS

Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

This species, and in general many Hydractiniids, is easy to rear under laboratory conditions and is widely used for experimental biology as a laboratory animal. ♦

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