Proctonotus mucroniferus

Proctonotus mucroniferus (Alder & Hancock, 1844)

Proctonotus mucroniferus Loch Torridon, W. Scotland. Photo Gil Green. by Bernard Picton










































Proctonotus mucroniferus  (Alder & Hancock, 1844)

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 140858).

  • Venilia mucronifera Alder & Hancock, 1844
  • Zephyrina pilosa de Quatrefages, 1844

Body up to 15mm long, coloured yellowish brown, marbled and spotted with darker brown. The dorsum is pale yellowish brown, clouded and freckled with darker brown, and sprinkled with minute white dots. Rest of the body hyaline white, nearly transparent, with a few small brown spots on the head and the margin of the foot, mixed with more numerous opaque white dots. The back is depressed and slightly rough, while the sides are smooth and concave. Rhinophores are wrinkled and nodulose. Cerata are ovate or inversely pear shaped, with blunt tips and almost colourless, covered with sparse tubercular white points over the whole surface, and they grow along the projecting sides of the notum in a dozen transverse rows of three papillae each, very close at the base, those next to the back are large and inflated, the exterior ones very small. Two cerata larger than the rest are located in the rear side close to the tail. There are also 4 large elliptical tuberculated cerata passing round the head ahead of the rhinophores. All cerata but those ahead of the rhinophores show a yellowish digestive gland with undulated margins inside. Oral veil is small and strongly notched, covering two cylindrical oral tentacles surrounding the mouth. The foot is deeply grooved and bilobed, the sides rounded, tappering backwards to a fine tail. Prominent anus, located on the rear side of the dorsum.

Original specimen used for its description was found by a shallow depth dredge at Malahide, Dublin, Ireland, attached to a Halichondria panicea sea sponge. It detaches the larger cerata when stressed, which are quickly replaced with apparently no adverse effects for the animal.


  • Proctonotus. From ancient Greek “proktos”, anus and “noton”, dorsum or back, stating that has the anus located dorsally.
  • Mucroniferus. From ancient Latin “mucron”, mucron (a short, more or less sharp and well differentiated tubercle that ends abruptly) and “fero”, to bring, to carry.

Eminently an Atlantic and extremely rare species, it has only been reported from Malahide Bay, Ireland (Alder & Hancock, 1844), in Clyde Bay (Thompson & Brown, 1984), in Loch Torridon, Scotland (top photo), in Vikaneset, Kristiansund, Norway (Christian Skauge, 2007 in Sea Slug Forum) and on the French Atlantic coast in Saint Vaast la Hougue (Quatrefages, 1844) and Roscoff (Vayssière, 1913). The report of Fez (1974) in the coasts of Finisterre (Galicia, Spain) is most probably a confusion since it alludes to a report by Vayssière in Roscoff (Finistère, France).

Known georeferenced records of the species: Proctonotus mucroniferus
: GROC 2010-2011
: Enric Madrenas
: João Pedro Silva
: Bernard Picton
: Manuel Ballesteros.
: M@re Nostrum
: Altres fonts
: Marine Regions

Similar species
Janolus hyalinus, with a sensorial crest between the rhinophores known as “caruncle”, absent in P.mucroniferus.


    Western Mediterranean: ☆☆☆☆☆
    Eastern Mediterranean: ☆☆☆☆☆
    Atlantic Ocean: ★☆☆☆☆

This chart displays the monthly observation probability for Proctonotus mucroniferus based on our own records.

More pictures


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Further reading

Cite this article as:

Ballesteros, M., Madrenas, E. & Pontes, M. (2023) "Proctonotus mucroniferus" in OPK-Opistobranquis. Published: 20/10/2014. Accessed: 20/04/2024. Available at (

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