June 8, 2001
From: Paul Young
We came across this critter diving off Jamestown, Rhode Island, USA on May 11, 2001. We were in 10 meters of water. The animal is about 3 cm long.
It doesn't appear in any of my books. Can someone identify it?
Young, P., 2001 (Jun 8) Pleurobranchaea from Rhode Island, USA. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4483
This is a species of Pleurobranchaea,
possibly P. tarda Verrill, 1880 which is known from the West Atlantic from Martha's Vineyard to south of Cuba, East Atlantic from Ghana & Cape of Good Hope, Sth Africa. Intertidal to 1450 meters.
Unfortunately there appears to be no good distinguishing external features separating it from P. obesa which also occurs in the east coast of North America. Marcus & Gosliner (1984) say the mantle edge 'often forms an exhalant siphon over the anal opening and the tip of the gill. Their accompanying photo (Fig 4) has apparently been reversed in the printing process with the gill and siphon appearing on the left side. Your photos show this very feature, but whether it is really species specific or just a feature of the genus I couldn't say.
The best I can say is that it is a species of Pleurobranchaea. Any more would require the animal to be dissected. They are a fairly advanced group of pleurobranchs and if you have a look at the other messages on this page and use the Species List to look at the other species of the genus on the Forum you will find quite a bit of biological information. I have included enlargements of the gill tip and the right rhinophore to show their structure.
Marcus, E. & Gosliner, T.M. (1984) Review of the family Pleurobranchaeidae (Mollusca, Opisthobranchia). Annals of the South African Museum, 93(1): 1-52.
Apart from the sterling efforts of Betsey Hansen we have very few photos of sea slugs from the temperate waters of the east coast of the USA. If you have others you are willing to share with us they would be very welcome.