Janthina umbilicata d'Orbigny, 1841
Overview
This is a large, deep violet shelled, pelagic snail, 1 cm high. It lives in the pleuston and does not posses swimming fins. The dextral shell is not depressed with about 4 whorls. The body whorl increases rather rapidly, the aperture is large and oval, with straight columella. There is a small keel and an incision in the outer aperture rim. The operculum is absent in adults. It is a carnivorous species which predates on relatively large floating prey animals. This species occurs in the warm waters of all oceans (Janthina umbilicata colour).
Taxonomic Description
The shell is dextral, globose-ovate, very thin and transparent and deep violet (Janthina umbilicata). The spire is not quite as tall as Janthina exigua. The edge of the aperture runs from the suture downwards in an oblique direction to the middle of the whorl, then it curves obliquely forwards to the columella. The columella is straight, slightly reflected and umbilicated. The apex is well defined, the body whorl is large and the aperture is wide. The surface of the shell is faintly striated, the striae follow same course as the edge of the aperture. At the level of the indentation of the aperture the striae curve backwards and upwards to form a keel around the large body whorl (Janthina umbilicata 1, Janthina umbilicata 2). The operculum is absent in adults, the jaws are large, the radula is small and the teeth are numerous but the central teeth are lacking.
Shell height up to 9 mm, height aperture up to 6 mm, width of aperture up to 4.5 mm.
Juveniles
The juveniles have a dextrally coiled shell. A special description is not available.
Reproduction
This species is a viviparous, protandric hermaphrodite.
Ecology
This species is a carnivorous surface dweller which feeds on Velella, Janthinidae, Haliobatidae and Siphonophora.
Distribution
This species is found in warm water of all oceans including the Red Sea, see the Janthina umbilicata map.
Types
Janthina umbilicata d'Orbigny, 1841: 414.
Types not indicated.
Type locality: probably from the Cuba and Antillian waters.