SKIN MORPHOLOGY AND CYTOLOGY IN MARINE EELS ADAPTED TO DIFFERENT LIFE-STYLES

Background: Moray eels (Muraenidae, Pisces) are among the largest bent hic predators of littoral habitats, particularly in warm seas and cora l reefs. They seek food either by olfaction or visually, moving across the pebbles and rocks. Their skin forms a strong, protective layer. T his study examines the comparative morphology and cytology of the skin of moray eels adapted to such lifestyles. Methods: The studied eels w ere collected in the Gulf of Aqaba, Red Sea and sacrificed by an overd ose of MS222. Skin selections from different body sites were dissected and fixed for light and electron microscopy. Results: The skin of mor ay eels (Siderea grisea, Lycodontis nudivomer, Gymnothorax undulata, G . hepaticus, Rhinomuraena amboensis) and the heterocongrid garden eel (Gorgasia sillneri) reveal considerable adaptation of the integument t o their different Lifestyles, on and within the various bottom substra te. All the eels studied featured skin comprising a multilayered, stra tified epidermis and a compact, collagenous dermis, with thickness of up to 2 mm, much thicker than that observed in their free-swimming rel atives. The thickness and cytology of the two skin layers differ in th e various species on different body sites within the same species and also changes with age. Pronounced differences were observed in the num ber and type of mucus-producing cells in the epidermis. In S. grisea, the entire body is covered by a multiple layer of goblet cells, wherea s in G. sillneri, sacciform cells predominate, particularly on the cau dal part of the body where they form an uninterrupted layer, replacing the supporting cells that surround them. These cells are also dominan t in R. amboensis. The two latter species are sand-dwelling and the co pious production of slime from these cells enables the adhesion of san d granules to their burrow walls. In Gorgasia, a special morphological adaptation was also observed in its pointed tail-end where the very s trong dermal collagen forms a rigid device for digging tail-first into the sand. Conclusion: The differing thicknesses and cytological devel opments in the skin of marine eels protect these crawling and digging creatures against abrasive interaction with their sea bottom habitat. (C) 1996 Wiley-Liss, Inc.