Janthina janthina
Encyclopedia
Janthina janthina, common name
the common purple snail, is a species
of holoplankton
ic sea snail
, a marine
gastropod mollusk in the family Janthinidae
, the violet snails or purple storm snails.
These snails are a unique part of the pleuston
, organisms living on or at the very 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.
Physalia physalis.
to maintain their positions at the surface of the ocean where they are predatious
on the hydrozoans. In addition to the bubble raft, only the veliger
, or larval stage, has an operculum
, and the shell is paper-thin to allow the animal to float upside down at the surface.
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
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 snail begins life as a male and later changes to the female of the species. The eggs are held by the female until they develop into a larval form.
The shell is almost smooth with a slightly depressed-globose shape. It is thin and delicate, and is without an operculum.
The colour of the shell is violet, with a paler upper surface.
The height of the species shell is up to 38 mm, the width to 40 mm.
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
the common purple snail, is a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of holoplankton
Holoplankton
Holoplankton are organisms that are planktonic for their entire life cycle. Examples of holoplankton include some diatoms, radiolarians, some dinoflagellates, foraminifera, amphipods, krill, copepods, and salps.-Sources:Asexual Holoplankton:...
ic sea snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
, a marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
gastropod mollusk in the family Janthinidae
Janthinidae
Janthinidae, common name the purple snails or violet snails, are a family of pelagic sea snails, marine gastropod mollusks in the informal group Ptenoglossa of the clade Hypsogastropoda....
, the violet snails or purple storm snails.
Distribution
This species is found worldwide in the warm waters of tropical and temperate seas, floating at the surface. They are often found in large groups and sometimes become stranded on beaches when they are blown ashore by strong winds.These snails are a unique part of the pleuston
Pleuston
Pleuston are the organisms that live in the thin surface layer existing at the air-water interface of a body of water as their habitat. Examples include some cyanobacteria, some gastropods, the ferns Azolla and Salvinia and the seed plants Lemna, Wolffia, Pistia, Eichornia and Hydrocharis. The...
, organisms living on or at the very 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, drifting on the surface of the ocean, where they feed upon pelagic hydrozoans, especially the by-the-wind sailor Velella velella and the Portuguese man o' warPortuguese Man o' War
The Portuguese Man o' War , also known as the Portuguese man-of-war, man-of-war, or bluebottle, is a jelly-like marine invertebrate of the family Physaliidae...
Physalia physalis.
Description
Janthina janthina is a member of the Janthinidae family, snails that trap air bubbles with a layer of clear chitinChitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
to maintain their positions at the surface of the ocean where they are predatious
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
on the hydrozoans. In addition to the bubble raft, only the veliger
Veliger
A veliger is the planktonic larva of many kinds of marine and freshwater gastropod molluscs, as well as most bivalve mollusks.- Description :...
, or larval stage, has an operculum
Operculum (gastropod)
The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...
, and the shell is paper-thin to allow the animal to float upside down at the surface.
The snail's shell is reverse countershaded
Countershading
Countershading, or Thayer's Law, is a form of camouflage. Countershading, in which an animal’s pigmentation is darker dorsally, is often thought to have an adaptive effect of reducing conspicuous shadows cast on the ventral region of an animal’s body...
, because of its upside-down position in the water column. There is a light purple shade on the spire
Spire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
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 snail begins life as a male and later changes to the female of the species. The eggs are held by the female until they develop into a larval form.
The shell is almost smooth with a slightly depressed-globose shape. It is thin and delicate, and is without an operculum.
The colour of the shell is violet, with a paler upper surface.
The height of the species shell is up to 38 mm, the width to 40 mm.
