Pleurobrachus weberi

Photo by Bob Yin taken at Pearl Farm Resort , Mindinao, Philippines during a night dive
Pleurobrachus weberi, Bergh 1905

At first glance we called this pleurobranch (or side-gilled sea slug) species Pleurobranchus forskalii (Ruppell & Leuckart, 1828), but after closer examination and a glass of Chardonnay, I believe what we are looking at is a new undescribed species.

P. forskalii, while quite variable in color, ranging from white as seen in Wells & Bryce to deep maroon, almost black, seen in Gosliner, Behrens & Williams, P. forskalii always has some semblance of a pattern of semicircles on the notal surface. These markings may vary again from black, or even the same color as the body, reversing to opaque white. Rarely is there any color decoration along the margin of the notum. The dorsal surface bears low tubercles, which, with the semicircles can form what appear to be large scales.

Uncle Bob's critter shown here from Pearl Farm Resort, Davao City, Mindanao, Philippines, has a smooth dorsal surface, and a pattern of evenly distribute bulls-eyes across the dorsal surface. These bulls-eyes are complete circles, not semi-circles as in P. forskali, and there is a wide band of mesh shaped white lines around the edge of the dorsum. More notably the bulls-eyes are formed of two circles, an always widely separated by an open space, not connecting as in P. forskalii. These really look the artwork of child with a piece of white chalk.

P. forskalii has a wide distribution occurring in Tanzania, the Red Sea, Australia, Fiji, New Guinea, Indonesia, the Philippines, Guam, and Japan. It is a large pleurobranch, reaching 15 cm in length, and is nocturnal, foraging at night on sand and rubble bottoms.

Well let us know what you think? Has Bob come up with another new species for the growing list of branchs from the extremely diverse waters of the Philippines, or can we add one more variant to the wardrobe of Pleurobranchus forskalii?

Dave Behrens
Aug. 1998
Danville, Calif

WEBMASTER'S NOTE: By chance while visiting San Diego Brancher Jim Lance earlier this year, I had an opportunity to look through Bergh's 1905 Voyage of the Sibogae. There is a line drawing of a Pleurobranch that was a close fit to our animal being featured in the BOW. The original year of publichation of the BOW was 1998. For the time being the animal is being moved from undescribed to Pleurobranchus weberi as per Bergh, 1905

Jun. 2002
San Diego, Calif

As an active member of the San Diego Underwater Photographic Society, Robert Yin has been taking underwater photographs world-wide for over 30 years, specializing in the Philippines. His photographs have appeared in many magazines and books including Skin Diver, Ocean Realm, Discover Diving, Philippines Airlines' Mabuhay Magazine, Action Asia, Asian Diver, National Geographic, Trauchen, Espacio Profundo, Sport Divers Journal, and scientific journals.

He has won many photographic awards including Nikon Photo Contest International. He was a presenter at the 1986, 1990, 1992, 1994 and 1998 San Diego Underwater Film Festivals. His photos have been exhibited in galleries including Sea Center Santa Barbara, S. Birch Aquarium-Museum San Diego, Cabrillo Aquarium, Manila Hotel and the Monterey Aquarium.

His 1997 books are Marine Life for Young Readers by Dominie Press, USA; and Beneath Philippines Seas by Bookmark, Philippines eMail:

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Text courtesy of Dave Behrens
Photos courtesy of Bob Yin

David W. Behrens

Author: Pacific Coast Nudibranchs
Co-Author Coral Reef Animals of the Indo Pacific
Propriator of Sea Challengers Natural History Books !

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