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Cliopsis krohni Troschel, 1854 morpha krohni Troschel, 1854


This is a medium sized naked pelagic snail, up to 2.4 cm long, with a completely transparent body and the visceral organs are seen through the body wall. The body is oval shaped,balloon-like and the posterior gill is ring-shaped. It is a carnivorous species, living in all oceans in the upper water layers.

Taxonomic Description

Posterior gill present, lateral gill absent. The posterior gill is hexagonal with four rays without fringes. The visceral mass is yellowish-brown, and fills up almost the whole body. When the specimens are not yet full grown, the visceral mass nearly reaches the body pole, but then it does not fill up the entire body. The body integument is slightly coloured or colourless and semi-transparent. The posterior tentacles are retractile, the anterior ones are very small (Cliopsis k. krohni drawing). There are no acetabuliferous arms or buccal cones. The proboscis, when evaginated, is twice as long as the body or even longer. The digestive tube in the proboscis may reach a length of 110 mm. The length of the oesophagus does not permit the buccal organs to become evaginated like the proboscis, they always stay at its basis. A median footlobe is lacking, but a well developed median tubercle with longitudinal grooves is present. The Cliopsis k. krohni radula formula varies between 6-1-6 and 4-1-4. The median plates are tricuspoid. There are about 20 transverse rows of teeth. The first lateral teeth differ from the other laterals by a denticle at the medial side in the middle of the head cusp. The hook sacs are shallow with about 40 to 60 hooks. The egg mass is a round gelatinous mass about 8 mm in diameter.
Body length up to 24 mm.


The larval form of this morph is described probably as Trichocyclus mediterraneus. The caudal ciliary larval-band persists in sexually mature specimens.


This species is a protandric hermaphrodite.


This species is a carnivore.


This species is represented by three morphs, but their discrimination is too uncertain to give valuable maps for the three morphs separately. The common sympatry of the morphs should be mentioned. In the W Mediterranean the half-full-growns (morpha krohni) animals are more common than elsewhere. This species is found in all oceans between 50°N and 50°S and in the Mediterranean. Its abundance is higher in offshore areas than in the centres of the oceans. Penetration into the Red Sea, Arabian Sea and Bay of Bengal, and the Caribbean, is not known, while avoidance of cold influences in the south is evident. Central water masses seem to be avoided too. See the Cliopsis k. krohni map.


Cliopsis krohni Troschel, 1854: 222, pl. 10, figs. 1-12.
Type: From the original description it may be concluded that only one specimen was mentioned.
Type locality: Messina, Coll.:? Troschel.

Cliopsis krohni krohni