Janthina janthina

Violet snail, from Lesueur (1807 ): Voyage de découvertes aux terres Austral

The violet snail ( Janthina janthina ), also referred to as a raft snail is a snail of the genus violet snails ( Janthina ) in the family of raft snails ( Janthinidae ). The pelagic life, violet -colored worm drives with the help of a formed from mucus raft on the sea surface of the oceans. They feed on cnidarians.

Dissemination

The violet snail occurs in temperate to tropical regions of all three oceans and in the Mediterranean.

Appearance

Like most snails has the violet snail a right-handed case. It is approximately conical, but can vary in shape and has a flat top. The up to four whorls ending in a nearly triangular to rounded, wide mouth housing. The body handling is great. The spindle is straight, often with a slight twist. The violet -colored, thin body is almost smooth with clearly visible growth lines. The shell is up to 31 mm high, the mouth up to 22 mm wide. During the veliger larva still has an operculum, this is no longer present in the adult animal.

The screw has a large head on a very flexible neck. The very small eyes are located at the base of the sensor.

The screw forms the body's own mucus chitinhaltiges a raft made of transparent, air-filled bubbles, where it is connected with the ventral side up and drives the water surface. Therefore, the screw is counter- chat advantage vice versa.

Life cycle

The screw is first a male and then a female. Violet snails do not have a penis, but the sperm reach across the water from the male to the female. While other types of Janthina attach up to two and a half million eggs on their raft, is Janthina janthina ovoviviparous, ie the eggs develop in the oviduct of the mother, are repelled to numerous bursting egg packages with fully developed veliger larvae, out of which this swim. When open the egg packets already in the fallopian tube, the larvae swim out from the genital opening of the dam. From a package arrive about 20 or more larvae, which have a shell diameter of 100-230 microns. It follows a prolonged period of veliger larva as zooplankton until evolved from it the final screw.

At the time of metamorphosis the juvenile snail forms a long slimy stalk with a bale of air bubbles at the end, by means of which the animal reaches the surface, where the final raft is formed. The air-containing mucus bubbles are formed with the foot, are being used for a bubble for about 10 seconds. Loses the worm their raft, they can only be a new form when it has contact with the water surface and thus to the air.

Food

The violet snail feeds on cnidarians, especially sailing jellyfish and siphonophores, including the highly toxic Portuguese galley. In addition, other pelagic snails, and sea water striders are attacked.