''Janthina janthina'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

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 lif ...

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the family

Epitoniidae Wentletraps are small, often white, very high-spired, predatory or ectoparasitic sea snails, marine gastropod mollusks in the family Epitoniidae.Gofas, S. (2010). Epitoniidae. In: Bouchet, P.; Gofas, S.; Rosenberg, G. (2010) World Marine Mollu ...

. 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 contrast ...

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 known as pleuston, are organisms that live at the surface of the ocean or an estuary, or at the surface of a lake, river or pond. Neuston can live on top of the water surface or may be attached to the underside of the water surface. ...

, organisms which live on or near the surface of the water, because of their relatively large size. They have veliger, 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 (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

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

hydrozoa Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specializ ...

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

Velella velella ''Velella'' is a monospecific genus of hydrozoa in the Porpitidae family. Its only known species is ''Velella velella'', a cosmopolitan free-floating hydrozoan that lives on the surface of the open ocean. It is commonly known by the names sea r ...

'', and the Portuguese man o' war, ''

Physalia physalis The Portuguese man o' war (''Physalia physalis''), also known as the man-of-war, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is considered to be the same species as the Pacific man o' war or blue bottle, which is ...

''.

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 where 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 the ...

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 An amphiphile (from the Greek αμφις amphis, both, and φιλíα philia, love, friendship), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'') properties. Such a compoun ...

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

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

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

. In addition to the bubble raft, only the

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 ...

, 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 Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, and ...

, 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. Spires are ...

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