Pleurobranchaea from Argentina

November 23, 2009
From: Nahuel E. Farias


I´m interested in to determine which species is this, I believe is an alien one. A few months ago I started to find many of these in an area that I dive regularly and I did never see it before. I´m sure it is a Pleurobranchaea but does not looks like P. inconspicua, which is the only recorded in this zone to the best of my knowledge.

Any idea is gratefully received

Locality: Mar del Plata, 5 meters, Argentina, Southwestern Atlantic, 12 September 2009, Rocky Boulders inside Port. Length: 93 mm. Photographer: Nahuel E. Farias.

Nahuel E. Farias

Farias, N.E., 2009 (Nov 23) Pleurobranchaea from Argentina. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Nahuel,

Tha lack of a hooked spur on the posterior part of the foot would suggest is not P. inconspicua. Although an 'alien introduction' could be one explanation, another could be that you are witnessing a natural event where a species is sometimes present and then may disappear for some years, perhaps because of some local event or irregularity of currents etc. Unfortunately species of Pleurobranchaea are not that easy to identify even when the anatomy is known. For example, Marcus & Gosliner (1984), in the only review of the genus, consider P. hedgpethi Abbott, 1952 and P. gela Marcus & Marcus 1962 to be synonyms of P. inconspicua and state that anatomical differences that the Marcus's had previously reported in the reproductive systems of P. hedgpethi and P. gela were probably the result of contraction in the preserved animals.

Marcus's specimens of P. inconspicua from Brazil (which they named P. hamva Marcus & Marcus, 1957) is the closest record I can find of a Pleurobranchaea to yours. It is possible yours is one of the other species described from further north in the west Atlantic but is also possible it is a species which occurs on the southwest coast of Sth America, but I don't think any species have been described from there.

All I can suggest is for you to contact a local natural history museum and see if they will add some specimens to their collections for future research. It would also be valuable to have them include some copies of your excellent photos, as one of the problems with research on these species is the lack of information on the shape and colour of the living animals.

Also if you have photos of P. inconspicua they would be a valuable addition to the Forum.

  • Marcus, E. and E. Marcus (1957). Sea-hares and side-gilled slugs from Brazil. Boletim do Instituto Oceanografico 6(1-2): 3-48.
  • Marcus, E. and T. M. Gosliner (1984). Review of the family Pleurobranchaeidae (Mollusca, Opisthobranchia). Annals of the South African Museum 93(1): 1-52,Figs1-25.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Nov 23). Comment on Pleurobranchaea from Argentina by Nahuel E. Farias. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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