Pleurobranchaea from New York

July 29, 1999
From: Betsey Hansen

Here is a Nudibranch that I can't identify. These slides were also taken in the Northwestern Atlantic off Long Island New York. I have only seen this nudibranch twice. Both times were last summer. The first time was in May (spring). I found three different ones, two of which were crawling around on mussel beds and the third was hidden behind a piece of seaweed.
Unfortunately, I didn't have my camera with me at the time. The second sighting was late last summer (September). I only found one at that time, but took several pictures. One shot shows what I believe to be this Nudibranch's eggs.

When I tried to move the Nudibranch to get a better look at it, it swam back to the rocks where it was hiding. It was amazing. I have not found this Nudibranch this year nor have I found it's eggs. I have searched through the entire slug site, but I cannot find anything close to it. Please let me know
what you think.
Best Regards,

Hansen, E.P., 1999 (Jul 29) Pleurobranchaea from New York. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Betsey,
Sorry you had to search the whole site and still have no luck. I have just prepared a page on an Australian and New Zealand species Pleurobranchaea maculata. Have a look there for a bit of background on a related species.

Your animal is a species of Pleurobranchaea, probably Pleurobranchaea obesa Verrill, 1882, but species in this genus are difficult to determine from external features. Hopefully someone from your part of the world wil recognise the animal from your photos and correct or confirm my identification.

The egg ribbon in which you can see the spiral coil of little white eggs is interesting because species of Pleurobranchaea seem to have one of two different shaped egg masses. Pleurobranchaea bubala from southern Africa (Marcus & Gosliner, 1984) and Pleurobranchaea japonica from Japan (Tsubokawa & Okutani, 1991) have a cylindrical egg ribbon similar to your photo, while P. californica has a flattened dorid-like ribbon which is attached along one edge in a sinuous band (Chivers, 1967).

Species of Pleurobranchaea belong to a group of Sea Slugs (Order Notaspidea) which are sometimes called the side-gilled slugs because they have a large gill on the right side of the body beneath the mantle skirt. Good pictures of the gill are found on the Pleurobranchus forskalii page. Some side-gilled slugs can swim when disturbed. As you obviously witnessed, it is a spectacular sight. One other point is that these slugs are not nudibranchs. They are Opisthobranch Sea Slugs but the Order Nudibranchia are a separate evolutionary line of Sea Slugs. If you are confused, or interested, the page with the Species List is arranged to show the relationships between the different groups of Sea Slugs. The aim, if I get time, is to prepare some general pages on the orders and families so that newcomers to th world of Sea Slugs do not just drown in a sea of scientific names.

Best wishes,
Bill Rudman.

* Cattaneo-Vietti,R; Burlando,B; Senes,L (1993): Life history and diet of Pleurobranchaea meckelii (Opisthobranchia: Notaspidea). J. Moll. Stud. 59, 309-313.
* Chiver, D.D. Observations on Pleurobranchaea californica MacFarland, 1966 (Opisthobranchia, Notaspidea). Proceedings of the California Academy of Scineces, 32(7): 515-521.
* Gosliner,TM (1985): Redescription and systematic position of Pleurobranchaea obesa (Verrill, 1882) (Opisthobranchia: Pleurobranchaeidae). The Veliger 28(1, 1 July), 109-114.
* Marcus, E. & Gosliner, T.M. (1984) Review of the family Pleurobranchaeidae (Mollusca, Opisthobranchia). Annals of the South African Museum, 93(1): 1-52.
* Tsubokawa,R; Willan,RC; Okutani,T (1992): Taxonomy of the two species of Pleurobranchaea in Japan (Gastropoda: Notaspidea: Pleurobranchidae). Venus, The Japanese Journal of Malacology 50(4), 249-263.

Bill Rudman.

Rudman, W.B., 1999 (Jul 29). Comment on Pleurobranchaea from New York by Betsey Hansen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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