Polycera atra from California

July 12, 2004
From: Chris Grossman

On Saturday April 3, 2004 I was on the Sea Divers trip to Santa Barbara Island, [California] aboard the Great Escape. It was the fourth dive of the day and we were anchored in about 35 feet of water approximately 100 yards North of the MPLA area at a dive site know as White Rock. The visibility was only about 20 feet, and the water was a bit green. The water temperature was about 56°F. It was also quite a bit of surge and many particulates in the water.

As I swam along I first noticed a golden gorgonian with what appeared to be a plant growing on it, but turned out to be the Bugula bryzoan. I thought this was unusual so I moved in for a closer look. Getting closer I noticed the white egg masses on the Bugula, and then moving closer I noticed the Polycera atra nudibranchs, a species I had never personally observed. Bugula on the gorgonian and the nudibranchs appeared very unique to me so I took a series of photos.

Chris Grossman

chris@diver.net

Grossman, C., 2004 (Jul 12) Polycera atra from California. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12608

Thanks Chris,
It is a nice series of photos showing the egg ribbon and the food bryozoan of this species.

Your animals are much darker than others on Forum but MacFarland (1966) discusses how there is a colour range from animals which are dark grey black with white lines to white with black lines. He notes that in his experience dark ones are from Monterey Bay while lighter ones are usually from 'more southern waters'. I don't know if more recent observations support his observations.
Best wishes
Bill Rudman

Rudman, W.B., 2004 (Jul 12). Comment on Polycera atra from California by Chris Grossman. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12608

Factsheet

Polycera atra

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