MarLIN

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

A sea slug (Janolus cristatus)

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

Summary

Description

Janolus cristatus is a semi-transparent nudibranch growing to at least 7.5 cm. The body is oval and flattened. There are numerous swollen cerata, each with a central thin dark thread of digestive gland. The cerata tips contain an irridescent bluish-white pigment. Similar patches of pigment are found on the back, between the cerata and in the head region. The lamellate rhinophores are especially large and conspicuous, non-retractile and without sheaths. A coarsely ridged, sensory cocks comb-like structure called a caruncle lies between the rhinophores, which is unique to Janolus species.

Recorded distribution in Britain and Ireland

Recorded from most British and Irish coasts except the southeast, reaching its northern distribution limit around the Shetland Isles.

Global distribution

Recorded from southern Norway, along the Atlantic French coast to Morocco. In the Mediterannean Sea from southern France and the Bay of Naples.

Habitat

Janolus cristatus lives in shallow sublittoral conditions, especially on sheltered rocky coasts. They feed on erect tufted bryozoans such as Bugula and Cellaria species.

Depth range

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Identifying features

  • A large species up to 7.5 cm long.
  • The body is pale brown or cream in colour but the rhinophores are darker, tending towards amber.
  • Oval in outline and flattened dorso-ventrally.
  • Cerata extend across front of body, each with a central thin dark thread of digestive gland.
  • Cerata tips with irridescent bluish-white pigment.
  • Lamellate rhinophores are large, conspicuous and non-retractile.
  • Caruncle between rhinophore bases.

Additional information

Spawning has been recorded from April to September and in December (Thompson & Brown, 1984). The egg-mass contains a series of bead-like white or pale pink ovoids, each being a capsule containing up tp 250 separate individual spherical eggs (ova). The spawn is wound in a wavy circle pattern (Thompson & Brown, 1984).

Listed by

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Further information sources

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Bibliography

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

  2. 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.]

  3. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid

  4. MarLIN (Marine Life Information Network), 2005. SEArchable BEnthic Data (SEABED) Map [on-line]. Data Access Sub-programme, Marine Life Information Network for Britian and Ireland http://www.marlin.ac.uk,

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

  6. Picton, B. E. & Morrow, C.C., 1994. A Field Guide to the Nudibranchs of the British Isles. London: Immel Publishing Ltd.

  7. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin., http://www.itsligo.ie/biomar/

  8. Rudman, W.B., 1999c. Janolus cristatus [on-line]. http://www.seaslugforum.net/factsheet.cfm?base=janocris,

  9. Thompson, T.E. & Brown, G.H., 1984. Biology of Opisthobranch Molluscs, vol. II. London: Ray Society.

Citation

This review can be cited as:

Oakley, J.A. 2005. Janolus cristatus A sea slug. 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/2154

Last Updated: 04/11/2005