MarLIN

information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Violet snail (Janthina janthina)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.

Summary

Description

Janthina janthina is a small snail. It's shell can be up to 4 cm high and 3 cm broad. The shell is globular, fragile and thin with a dark blueish-purple colouration which is darker at the base. The surface of the shell apears smooth but may possess regular growth lines and irregular spiral grooves, especially at the edge of the last whorl. The shell can be high or low with the last whorl constituting 75-80% of the the height in high shells, and aproximately 90% in low shells (Graham, 1988). The aperture would be 45% and 70% respectively (Graham, 1988). The protoconch (whorls at shell apex formed by the larval snail) axis is slanted. The large aperture is angular with a thin lip and small umbilicus, which is where the outer lip and columella meet.

The head of the violet snail has a long cylindrical snout with a terminal mouth. The tentacles are forked, have no eyes and project half way along its side's. The foot has a broad anterior and tapers to a posterior point. There is a broad depression or funnel at the anterior part of the sole, where the float is secreted. The posterior of the sole has longitudinal grooves. The flesh of this species is deep violet or black and in adults the operculum is absent.

Recorded distribution in Britain and Ireland

Janthina janthina has a circumequatorial distribution and has been recorded from strandings after storms along the coasts of SW Ireland, SW Wales, SW England and as far east as the Isle of Wight.

Global distribution

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Habitat

Janthina janthina is a holopelagic species, drifting on the ocean surface. It floats uniquely by a raft of bubbles bound by mucus secreted from the foot, and preys on the pelagic coelenterates Velella velella and Porpita sp. The shells of this species can occasionally be found on the strandline particularly after prolonged south-westerly gales (Hayward & Ryland, 1995).

Depth range

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Identifying features

  • Up to 4 cm high; 3 cm broad.
  • Globular fragile, thin shell.
  • Shell dark purple.
  • Short spire of 6 whorls (protoconch).
  • Deep violet or black flesh.
  • Floats on ocean surface via a raft of bubbles and mucus.

Additional information

Janithina janthina is the commonest member of the Janthinidae family. This species is ovoviparous where the eggs develop within the females genital tract and later shed as veliger larvae from the left side of the mantle cavity (Graham, 1988). The males are aphallic (no penis) and produce spermatozeugmata that swim to the female and enter the genital tract. Therefore fertilization occurs before the eggs have left the ovary, suggesting the species is a protandrous consecutive hermaphrodite.

Listed by

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Further information sources

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Bibliography

  1. Graham, A., 1988. Molluscs: prosobranchs and pyramellid gastropods (2nd ed.). Leiden: E.J. Brill/Dr W. Backhuys. [Synopses of the British Fauna No. 2]

  2. Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.

  3. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  4. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  5. Moore, J. 2002. Porcupine Marine Natural History Society Newsletter. Porcupine Marine Natural History Society Newsletter, 11, pp13-14.

  6. National Biodiversity Network (NBN) Atlas website. Available from: http://www.nbnatlas.org.  Accessed 01 April 2017

Citation

This review can be cited as:

Rowley, S.J. 2007. Janthina janthina Violet snail. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/species/detail/2138

Last Updated: 26/06/2007