Phestilla lugubris
(Bergh, 1870)

Order: NUDIBRANCHIA
Suborder: AEOLIDINA
Family: Tergipedidae

DISTRIBUTION

Tropical Indo-West Pacific.

PHOTO

UPPER RIGHT: Koumac, New Caledonia, 30mm long, October 1993.
LOWER RIGHT: with egg ribbons, Koumac, New Caledonia, October 1993
LOWER LEFT: pair, 40mm long, on "home site" on Porites colony, Africana Bch, 1km S. Kunduchi Bch, Dar es Salaam, Tanzania, June 1978.
PHOTOS: Bill Rudman.

RELATED TOPIC

Coral-feeding

Widespread throughout the tropical Indo-West Pacific, P.lugubris feeds on colonies of the coral Porites, often in very shallow waters. Probably much more common than realised, it is very cryptically coloured and often hidden in crevices and beneath the coral blocks to avoid heavy fish predation.

Animals are often remain in pairs for many weeks and occupy a "home site". In the photo below are a pair on a colony of Porites. Note the intense white "homing scar" where the coral skeleton is completely obliterated, and the wide dull white area around the Phestilla where the coral polyps have been eaten. Each animal lays up to about 25 large egg ribbons. Veligers hatch after 7-9 days. The veligers are lecithotrophic (non-feeding) and spend between 7-21 days in the plankton.

If you look carefully at the cerata of species of Phestilla you will see that the tip is white and swollen. Microscopically, the normal cubical epithelial cells have been replaced by long, columnar glandular cells which exude a sticky, apparently defensive secretion. The typical aeolid cnidosac is absent, because the nematocysts in their coral food provide little protection from predators. In a remarkable convergence with the unrelated soft-coral feeding Phyllodesmium, species of Phestilla also produce sticky ceratal secretions and are able to autotomise (break off) their cerata when disturbed or roughly handled.

Reference:
• Rudman, W.B. (1981a) Further studies on the anatomy and ecology of opisthobranch molluscs feeding on the scleractinian coral Porites. Zoological Journal of the Linnean Society, 71: 373-412.

Authorship details
Rudman, W.B., 1999 (May 17) Phestilla lugubris (Bergh, 1870). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/pheslugu

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