Structure and function of skin in the pelagic sea snake, Hydrophis platurus

Abstract

We describe and interpret the functional morphology of skin of the Yellow‐bellied sea snake, Hydrophis platurus. This is the only pelagic sea snake, and its integument differs from what is known for other species of snakes. In gross appearance, the scales of H. platurus consist of non‐overlapping, polygonal knobs with flattened outer surfaces bearing presumptive filamentous sensillae. The deep recesses between scales (‘hinge’) entrap and wick water over the body surface, with mean retention of 5.1 g/cm of skin surface, similar to that determined previously for the roughened, spiny skin of marine file snakes, Acrochordus granulatus. This feature possibly serves to maintain the skin wet when the dorsal body protrudes above water while floating on calm oceanic slicks where they forage. In contrast with other snakes, including three species of amphibious, semi‐marine sea kraits (Laticauda spp.), the outer corneous β‐protein layer consists of a syncytium that is thinner than seen in most other species. The subjacent α‐layer is also thin, and lipid droplets and lamellar bodies are seen among the immature, cornifying α‐cells. A characteristic mesos layer, comprising the water permeability barrier, is either absent or very thin. These features are possibly related to (1) permeability requirements for cutaneous gas exchange, (2) reduced gradient for water efflux compared with terrestrial environments, (3) less need for physical protection in water compared with terrestrial ground environments, and (4) increased frequency of ecdysis thought to be an anti‐fouling mechanism. The lipogenic features of the α‐layer possibly compensate for the reduced or absent mesos layer, or produce layers of cells that comprise what functionally might be termed a mesos layer, but where the organization of barrier lipids nonetheless appears less robust than what is characteristically seen in squamates.

Novel vascular plexus in the head of a sea snake (Elapidae, Hydrophiinae) revealed by high-resolution computed tomography and histology

“…The epidermal microstructure is similar to that reported in the congeneric sea snake Hydrophis platurus (i.e. mesos layer absent or very thin; [12]) (electronic royalsocietypublishing.org/journal/rsos R. Soc. open sci.…”

“…The epidermal microstructure is similar to that reported in the congeneric sea snake Hydrophis platurus (i.e. mesos layer absent or very thin; [12]) (electronic supplementary material, figure S2 in data S2). Histology sections revealed that the MCVN in H. cyanocinctus predominantly consists of veins and small sinuses.…”

“…Sea snakes obtain significant amounts of oxygen through their skin and a modified epidermal microstructure, i.e. mesos layer absent or very thin (electronic supplementary material, figure S2 in data S2), may further facilitate gas exchange through the skin via a reduced permeability barrier [12].…”

New chromosome-scale genomes provide insights into marine adaptations of sea snakes (Hydrophis: Elapidae)

“…The skin is supplied by a dense network of capillaries, and a redistribution of blood flow (bypassing the lung) ensures the delivery of blood with favourable partial pressure gradients for gas exchange [ 9 , 18 ]. Further facilitating gas exchange is modification of the permeability barrier of the skin [ 55 , 56 ], specifically the inner layer composed of lipids and α-keratin [ 57 , 58 ]. Our PSG set includes the α-keratin encoding KRT24 gene, which has been lost independently in birds, crocodiles and mammals [ 59 , 60 ] but may play a role in cutaneous respiration in snakes.…”