''Janthina janthina'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

holoplankton Holoplankton are organisms that are planktic (they live in the water column and cannot swim against a current) for their entire life cycle. Holoplankton can be contrasted with meroplankton, which are planktic organisms that spend part of their l ...

sea snail Sea snails are slow-moving marine (ocean), marine gastropod Mollusca, molluscs, usually with visible external shells, such as whelk or abalone. They share the Taxonomic classification, taxonomic class Gastropoda with slugs, which are distinguishe ...

, a marine

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

in the family Epitoniidae. Its

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

s include violet sea-snail, common violet snail, large violet snail and purple storm snail.

Distribution

This species is found worldwide in the warm waters of tropical and temperate seas, floating at the surface. More specifically, the species is located in the tropical and subtropical Atlantic, Indian and Pacific oceans. They are often found in large groups and sometimes become stranded on beaches when they are blown ashore by strong winds. The snails are a unique part of the

neuston Neuston, also called pleuston, are organisms that live at the surface of a body of water, such as an ocean, estuary, lake, river, wetland or pond. Neuston can live on top of the water surface or submersed just below the water surface. In additio ...

, organisms which live on or near the surface of the water, because of their relatively large size. They have

veliger A veliger is the planktonic larva of many kinds of sea snails and freshwater snails, as well as most bivalve molluscs (clams) and tusk shells. Description The veliger is the characteristic larva of the gastropod, bivalve and scaphopod taxono ...

, or free swimming larvae, but the adults do not swim, and cannot create their rafts, except at the surface where air bubbles are available.

Habitat

These snails are

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

, drifting on the surface of the ocean, where they feed upon pelagic

hydrozoa Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline wat ...

, especially the by-the-wind sailor, ''

Velella velella ''Velella'' is a monotypic taxon, monospecific genus of hydrozoa in the family Porpitidae. Its only known species is ''Velella velella'', a Cosmopolitan distribution, cosmopolitan (widely distributed) free-floating hydrozoan that lives on the sur ...

'', and the

Portuguese man o' war The Portuguese war (''Physalia physalis''), also known as the man-of-war or bluebottle, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is the only species in the genus ''Physalia'', which in turn is the only genus in ...

, ''Physalia physalis''.

Description

''J. janthina'' is a member of the family Janthinidae, snails that trap air bubbles to maintain their positions at the surface of the ocean, where they are

predators Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

on hydrozoa. Powell A. W. B., ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979 . The air bubbles are stabilized by the secretion of

amphiphilic In chemistry, an amphiphile (), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'', nonpolar) properties. Such a compound is called amphiphilic or amphipathic. Amphiphilic c ...

mucins Mucins () are a family of high molecular weight, heavily glycosylation, glycosylated proteins (glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key com ...

which have evolved from epitoniid egg masses. This passive flotation is a particularly resource-efficient form of

animal locomotion In ethology, animal locomotion is any of a variety of methods that animals use to move from one place to another. Some modes of locomotion are (initially) self-propelled, e.g., running, swimming, jumping, flight, flying, hopping, soaring and gli ...

. In addition to the bubble raft, only the

, or larval stage, has an operculum, and the shell is paper-thin to allow the animal to float upside down at the surface. Janthina_janthina_01

The snail's shell is reverse countershaded, because of its upside-down position in the water column. There is a light purple shade on the

spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spire ...

of the shell, and a darker purple on the ventral side. The animal has a large head on a very flexible neck. The eyes are small and are situated at the base of its tentacles. The shell, which is violet, with a paler upper surface, is almost smooth, with a slightly depressed-globose shape. It is thin and delicate, and is without an operculum. The height of the species shell is up to 38 mm, the width to 40 mm. The snail begins life as a male and later changes into a female. The eggs are held by the female until they develop into the larval form.

References

External links

Species Spotlight: ''Janthina janthina'' - Bermuda Department of Conservation Services
{{Taxonbar, from=Q338482 Epitoniidae Gastropods described in 1758 Taxa named by Carl Linnaeus