Janthina pallida Thompson, 1841
Overview
This is a large, shelled, pelagic snail, 2.4 cm high. It lives in the pleuston and does not posses swimming fins. The dextral shell is depressed with about 4 whorls and is blue to violet. The body whorl increases rapidly so that the aperture is large and rounded. There is a small keel and a faint incision in the outer aperture rim. The operculum is absent in adults. It is a carnivore which predates on relatively large floating prey animals. This species occurs in the warm waters of all oceans (Janthina pallida 1).
Taxonomic Description
The dextral shell is globose and deep violet (Janthina pallida). The rim of the aperture, with a sinus slightly above the middle, curves regularly. The surface is relatively roughly striated by growth lines. The striae show a fish-bone pattern from the middle of the whorl. A low keel is seen on all whorls. The shell is thin and translucent. The apex is well defined, the body whorl is large, the aperture is wide (Janthina pallida 3, Janthina pallida 2). The operculum is absent in adults. The jaws is large, the radula is powerful and has numerous teeth, the central teeth are lacking.
Shell height up to 24 mm, aperture height up to 22 mm, aperture width up to 13.5 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 carnivore surface dweller, feeding on Velella (Janthina pallida on Velella), Janthinidae, Haliobatidae and Siphonophora.
Distribution
This species is found in the warmer waters of all oceans, though records from the Indian and Pacific Oceans are very rare. It is also known from the Mediterranean, see the Janthina pallida map).
Types
Janthina pallida Thompson, 1941: 96, pl. 2, fig. 2. (Janthina pallida holotype).
Syntypes: not located.
Type locality: Miltown Malbay, coast of Clare, Ireland.