A large, shelled pelagic snail without swimming fins. Shell dextral, conical, egg-shaped and has about five whorls. The spire is rather tall with well defined apex, the edge of the aperture is passing in an even curve to the columella with a deep middle incision [J.exigua-ventral].
The body whorl is large. The surface has regular deep furrows, and this makes it easy to separate this species from the others in the genus. The furrows slant from the suture backwards to the middle, where they form a sinus and where, in continuation with the bottom of the incision in the aperture there is a very inconspicuous keel. The aperture is wide. From there the furrows pass obliquely forwards to end at the umbilicus [J.exigua-furrow, Janthina exigua]. An operculum is absent in adults.
Radula without median teeth. The jaws are large.
Juveniles have a dextrally coiled shell; a special description is not available.
The dextral shell is very thin, translucent and dark violet.
Shell height up to 17 mm, aperture height up to 11 mm.
Janthina exigua is well adapted as a surface dweller living in the pleuston.
Warm water species; carnivorous, feeding on relatively large floating prey animals such as other Janthinidae, Halobatidae (Insecta), Siphonophora (Cnidaria) and Velella velella (Cnidaria: Hydrozoa).
Distribution in the North Sea
Unlikely to be found in the North Sea.
All oceans, between about 40°S and 50°N.
[After Van der Spoel et al., 1997]