Re: Conga lines

November 16, 2001
From: Bernard Picton


Hi Bill,
Concerning Celeste's message I saw Onchidoris bilamellata behaving like this off the Aran Islands, Co. Galway, Ireland in early September 2001. All the animals were about 10-15mm in length and they were aggregating to spawn. In places the entire seabed was covered with individuals all facing in the same direction like an army on the march! They were climbing up onto sponges and soft corals and anything firm sticking up off the seabed to lay eggs where the current would catch them. The seabed was flat limestone with some loose shelly gravel in a slight current. I guess the shelly gravel is partly barnacle plates.

At about the same time Jim Anderson saw the same thing off Scotland. If the population is continuous between us this must be the most common nudibranch on the planet!! ;-)

Onchidoris bilamellata is supposed to be circumboreal and to occur off the entire west coast of the USA so Celeste's animal could be this species.

Bernard

bernard.picton.um@nics.gov.uk

Picton, B.E. , 2001 (Nov 16) Re: Conga lines . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5688

Dear Bernard,
Thanks for these wonderful photos and observations. I have put two of your photos of the egg masses in a separate message. As I commented in Dave Behren's message, it looks like Pelseneer wasn't seeing things in 1922 when he reported this phenomenon.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Nov 16). Comment on Re: Conga lines by Bernard Picton . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5688

Factsheet

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