Thyca crystallina

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Thyca crystallina
Thyca crystallina in natural color on Linckia laevigata

Thyca crystallina in natural color on Linckia laevigata

Systematics
Subordination : Hypsogastropoda
Partial order : Littorinimorpha
Superfamily : Vanicoroidea
Family : Eulimidae
Genre : Thyca
Type : Thyca crystallina
Scientific name
Thyca crystallina
( Gould , 1846)
Housing of Thyca crystallina

Thyca crystallina (original combination Pileopsis crystallina ) is the name of a worm - type from the family of eulimidae (genus Thyca ), as Ectoparasite especially on Blue Starfish and rarely also the comet star lives.

features

As with Thyca ectoconcha and other representatives of the subgenus Bessomia , the snail shell of Thyca crystallina is about 12 to 14 mm in females, and in males only about a tenth as large as the shell of Thyca crystallina and very low with a wide mouth, giving it the shape of a Phrygian cap or upside down in a shallow bowl. The mouth of the very flat case is egg-shaped, the apex is pointed. Characteristic for the conical housing of Thyca crystallina are the longitudinal furrows and ribs on the surface, each of which has pearly nodules at intervals. The surface of the shell is colored blue, as is usually the case with the host animal - the blue starfish - but loses this color when stored and becomes white or transparent. The color obviously does not come from the host animal, because parasitic snails living on apricot-colored specimens of Linckia laevigata do not take on the color of the starfish.

The snail's snout is designed as a "false foot" with which it sucks itself extremely firmly on the host and in the middle of which there is an opening through which the proboscis (proboscis) is guided into the host. The snail has a rudimentary base and no operculum. The antennae are fused into a fold on which the eyes sit.

Distribution and way of life

Thyca ectoconcha is widespread throughout the Indo-Pacific , where its host animal, the blue starfish ( Linckia laevigata ) lives, and is occasionally found on the comet star ( Linckia multifora ). While as a young animal it often sits on the top of the host, as an adult it hugs the underside of the animal. In the middle of the pseudopod there is a hole through which the proboscis of the snail is pushed further through the skin of the host to its nutrient-rich hemal canal or into the surrounding perihemal system.

Development cycle

Thyca crystallina is of separate sex. The adult female lives firmly attached to the host and no longer moves. The dwarf male , which is only a tenth of the size , lives under its shell and its cloak at its front end and mates with its long, slender penis when necessary . The fertilized eggs develop into free-swimming Veliger larvae, which ensure the spread of the species, develop a protoconch typical of the Eulimidae and metamorphose into parasitic snails on other host starfish . The sex of the young can already be determined, because the males do not have blue, but whitish to crystalline housings, which also differ in shape from those of the females. The snails initially live on the upper side of the host's arm, usually near the center disc, but then migrate to the lower side, where the females align themselves with the starfish's mouth and the males take care of a female.

literature

Web links

Commons : Thyca crystallina  - Collection of images, videos and audio files