January 25, 2002
From: John Chuk
Looking back through my slides I found one of Phyllodesmium macphersonae apparently feeding on a soft coral. The specimen was found on a dive at Flinders pier, Victoria, Australia, on 21st April 1995. My notes from the time describe it as being found feeding on small, dark, soft coral polyps on a pier pylon at a depth of 3m.
The first image is an in situ shot of the specimen feeding. It is not very distinct as the specimen was somewhat hidden in the profuse growth on the pylon. This growth included red and brown algae, sponges, bryozoans, and the soft coral. Several polyps of the soft coral can be seen to the left of the specimen. They are dark grey-green in colour which does suggest that they contain zooxanthellae. If so they may be the source of the zooxanthellae found in the nudibranch.
The second image is a composite enlargement of several of the soft coral polyps seen in the first. They have the typical pinnate tentacles of soft corals. The polyps are up to 3mm in diameter and 3mm in height. They are supported on a stem. I am unable to identify them.
The third image was taken of the specimen after removing it from the pylon and placing it on the bottom beneath the pier. It measured 18mm in length and certainly looks packed with zooxanthellae. At the time I took these shots I didn't know that any nudibranch used zooxanthellae as an energy source. It is somewhat fortunate that I'm in the habit of taking in situ shots before moving an animal!
Chuk, J., 2002 (Jan 25) Phyllodesmium macphersonae - first feeding record. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6079
This is indeed another wonderful find. I have long puzzled over what this species eats. As you surmised it does indeed contain zooxanthellae and is one of the species in the genus in which the digestive ducts have developed a complex system of branching so that zooxanthellae can be placed in little 'gardens' in all parts of the skin which receive sunlight. This is the first record we have of its food. I will need to check its identity, but it reminds me it seems to be Erythropodium hicksoni [formerly known in Australia as Paryerythropodium] which is an encrusting soft coral forming thin leathery mats over large areas of the low intertidal and upper sublittoral regions of rocky shores in temperate Australia. It is often overgrown with algae, sponges and other growths. I'll let you know when I get this soft-coral's identity confirmed.
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