Skin morphology and cytology in marine eels adapted to different lifestyles.
BACKGROUND
Moray eels (Muraenidae, Pisces) are among the largest benthic predators of littoral habitats, particularly in warm seas and coral reefs. They seek food either by olfaction or visually, moving across the pebbles and rocks. Their skin forms a strong, protective layer. This study examines the comparative morphology and cytology of the skin of moray eels adapted to such lifestyles.


METHODS
The studied eels were collected in the Gulf of Aqaba, Red Sea and sacrificed by an overdose of MS222. Skin selections from different body sites were dissected and fixed for light and electron microscopy.


RESULTS
The skin of moray eels (Siderea grisea, Lycodontis nudivomer, Gymnothorax undulata, G. hepaticus, Rhinomuraena amboensis) and the heterocongrid garden eel (Gorgasia sillneri) reveal considerable adaptation of the integument to their different lifestyles, on and within the various bottom substrata. All the eels studied featured skin comprising a multilayered, stratified epidermis and a compact, collagenous dermis, with thickness of up to 2 mm, much thicker than that observed in their free-swimming relatives. The thickness and cytology of the two skin layers differ in the various species on different body sites within the same species and also changes with age. Pronounced differences were observed in the number and type of mucus-producing cells in the epidermis. In S. grisea, the entire body is covered by a multiple layer of goblet cells, whereas in G. sillneri, sacciform cells predominate, particularly on the caudal part of the body where they form an uninterrupted layer, replacing the supporting cells that surround them. These cells are also dominant in R. amboensis. The two latter species are sand-dwelling and the copious production of slime from these cells enables the adhesion of sand granules to their burrow walls. In Gorgasia, a special morphological adaptation was also observed in its pointed tail-end where the very strong dermal collagen forms a rigid device for digging tail-first into the sand.


CONCLUSIONS
The differing thicknesses and cytological developments in the skin of marine eels protect these crawling and digging creatures against abrasive interaction with their sea bottom habitat.
Fishelson
L
L
Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.
D000222:Adaptation, Physiological; D000818:Animals; D004524:Eels / Q000033:anatomy & histology* / Q000145:classification / Q000502:physiology; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D009093:Mucus / Q000378:metabolism; D012038:Regeneration; D012867:Skin / Q000033:anatomy & histology* / Q000166:cytology* / Q000648:ultrastructure; D014950:Wounds, Penetrating / Q000503:physiopathology