JANTHINA JANTINA, THE VIOLET “FLOWER” OF THE SEA: A MOST UNUSUAL GASTROPOD

This post is about the unusual gastropod Janthina janthina (Linnaeus, 1758). Its scientific name is derived from new Latin, janthina [feminine of janthinus], meaning violet-blue, and from the Greek word anthos [meaning flower]. Its common name is “violet sea snail” or “purple-storm snail.” This last moniker is explained below.

Janthina janthina is a holoplanktonic [pelagic] sea snail. It spends its entire life cycle as a passive floater at or near the surface of tropical and warm-temperate oceans throughout the world. All Janthina are born being males, but, as they develop, they become females. Although their larvae (referred to as veligers) swim, the adults cannot swim. This gastropod produces rafts made of bubbles derived from their own mucus. These rafts are commonly mistaken as eggs. They can be common in Mexico and Peru. In some cases, large groups (“colonies”) of them float together, thus after storms, they are prone to being stranded along beaches; hence the derivation of the name “purple-storm snails.” Their shells can be as big as height 38 mm and width 40 mm. Janthina janthina feeds on pelagic (floating) microscopic hydrozoans, as well as on jelly fish and the jelly-fish looking Portugese-Man-of War. The shell of Janthina absorbs the purple-color ink of their prey.

Life position of Janthina janthina. Image after Younge and Thompson (1976, pl. 5).

The very fragile, paper-thin shell (lighter-than-air) of Janthina janthina floats upside-down (with its spire down) during life. This position is just the opposite of most other gastropods. The Janthina janthina shell is also reverse countershaded: with the spire whorls light colored, and the basal whorl dark colored. This countershading is similar to that found in fish because it provides protection from predators by being nearly invisible to them.

Basal view of a Janthina janthina shell (2.5 cm wide) from Florida. The basal (purple side) of the shell faces the sky during the adult life of this gastropod.

Top view of the same Janthina janthina shell as shown above. This white side of the shell faces the ocean bottom when the shell is floating in the ocean.  

Side view (2.3 cm height) of the same Janthina janthina shell as shown above.

References Cited:

Linnaeus, C. 1758. Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Edition decima, reformata (10^th revised edition), vol. 1, 824 pp. Laurentius Salvius: Holmiae. Total pages 772

 Available online free at https://biodiversitylibrary.org/page/726886

Yonge, C.M. and T.E. Thompson, 1976. Living marine mollusks. William Collins Sons & Co., London, 288 pp.