IUCN threat status:

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Janolus is a genus of small to large sea slugs, or more accurately nudibranchs, marine gastropod mollusks, in the family Proctonotidae.[1]

The name Janolus is derived from the two-headed god Janus, in ancient Roman mythology.

Although these nudibranchs superficially resemble aeolid nudibranchs, this genus is in fact in the suborder Arminina.


Adult individuals of Janolus species can be between 2.5 cm to 8 cm long, depending on the species. They are semi-translucent and the body is covered in short cerata.

The color of the cerata varies according to the species: in Janolus fuscus the cerata are orange and white tipped, whereas in Janolus barbarensis they are orange and blue tipped.


Janolus species are found in many areas world-wide, including Europe, Australia, Japan and Africa.

The species Janolus fuscus is found from the Kenai Peninsula, Alaska to central California and also in northern Japan.[2]



This genus of nudibranch is found in shallow and subtidal waters.

Feeding habits[edit]

Janolus species feed on Bryozoa, moss animals.


In California, Navanax is a known predator of Janolus. Navanax tracks the slime of Janolus by using chemoreceptors. When Janolus is about to be caught, it rolls into a ball, leaving its cerata exposed.


Species in the genus Janolus include:[3][4]

Species brought into synonymy


  1. ^ a b Bouchet, P.; Gofas, S. (2012). Janolus Bergh, 1884. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=138379 on 2012-06-03
  2. ^ "Janolus fuscus". Sea Slug Forum. Retrieved 24 December 2006. 
  3. ^ "Janolus". Integrated Taxonomic Information System. 
  4. ^ Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1
  • Vaught, K.C. (1989). A classification of the living Mollusca. American Malacologists: Melbourne, FL (USA). ISBN 0-915826-22-4. XII, 195 pp.
  • Gofas, S.; Le Renard, J.; Bouchet, P. (2001). Mollusca, in: Costello, M.J. et al. (Ed.) (2001). European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification. Collection Patrimoines Naturels, 50: pp. 180–213


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