Epidermal and papillary dermal characteristics of the bowhead whale (balaena mysticetus)

Abstract

Skin samples from most body regions of the bowhead whale were examined. The epidermis is 2.7 to 50 times thicker than that reported in other cetaceans with both regional and individual variations in thickness. The thinnest areas examined (1 mm) occur on the eyelid margins and the thickest (25 mm) occur on the lower jaw. A distinctive parakeratotic stratum corneum with a thick underlying stratum spinosum (without a stratum granulosum) extends over the entire body surface. From a few dozen to several hundred epidermal lesions are present on all whales studied. A typical stratum basale of germinative keratinocytes (with melanocytes in pigmented areas) rests upon a well-defined basal lamina. Epidermal rod arrays arise from the basal keratinocytes which cover highly elongated dermal papillae and extend to the epidermal surface through the distal stratum spinosum and the stratum corneum. At least four diatom genera occur on and in the stratum corneum and lesion areas of different whales. The superficial dermis consists of a papillary layer with long (up to 13 mm) dermal papillae interdigitating with the epidermis from a basal area that is 2-4 mm in thickness. The number of dermal papillae per mm2 varies inversely with the thickness of the epidermis. Large diameter, sensory papillae packed with tortuous, highly elongated, encapsulated nerve end organs also interdigitate with the thin epidermal areas of the ventral surface of the rostrum, the upper and lower lip margins, and the upper and lower eyelid margins. Scattered, single, stiff hairs emerge from the skin only in specific, pigmented regions of the head.

Structure of the integument of southern right whales, Eubalaena australis

“…Although, researchers and Eskimo captains claimed that early season calves of bowhead whales had especially thick epidermis (Eschricht and Reinhardt, 1866;Haldiman et al, 1982Haldiman et al, , 1985Haldiman and Tarpley, 1993), the differences in epidermal thicknesses between seasonal and age groups of southern right whales were not significant. It is possible, however, that observers of the bowhead whale may have been referring to the epidermis of pre-ecdysal (pre-moult) neonates, which may be slightly thicker than in other calves (Reeb et al, 2005b).…”

“…The epidermis consists of three strata, compared with five strata in most terrestrial mammals. The outermost stratum has been referred to as the stratum corneum or the stratum externum, histochemically shown to contain keratin (Kleinenberg et al, 1964;Palmer and Weddell, 1964;Sokolov and Kalashnikova, 1971;Spearman, 1972;Simpson and Gardner, 1972;Ling, 1974;Greenwood et al, 1974;Haldiman et al, 1985;Haldiman and Tarpley, 1993), although the process of keratinization is incomplete (Harrison and Thurley, 1974;Albert et al, 1980;Migaki, 1981;Geraci et al, 1986;St. Aubin et al, 1990).…”

“…The dermis is a thick bed of dense white fibrous connective tissue, blood vessels, and adipose tissue (Haldiman and Tarpley, 1993), and is richly innervated (Parry, 1949;Palmer and Weddell, 1964;Giacometti, 1967;Simpson and Gardner, 1972;Haldiman et al, 1985). Collagen dominates with fairly stout bundles that are usually orientated parallel to the skin surface, although some are randomly arranged.…”

Seasonal and Ontogenetic Variation in Subcutaneous Adipose Of the Bowhead Whale (Balaena mysticetus)

“…Deep samples were taken at 4 cm and 7 cm above the hypodermis. Two intermediate blubber samples were taken (2 cm apart) from the middle between the superficial and the deep samples (Haldiman et al, 1985;Haldiman and Tarpley, 1993;Rosa, 2006). At each sampling location, 10 small, noncontiguous blubber samples (2 3 2 mm) were excised from surrounding adipose.…”

“…Anatomically, we define "blubber" as the reticular layer of the dermis and it thus excludes the epidermis, papillary layer of the dermis, and the hypodermis, by following similar definitions by Haldiman et al (1985) and Haldiman and Tarpley (1993). The hypodermis of bowheads, especially nursing and recently weaned individuals, exhibits additional adipose reserves which are structurally weaker than the blubber and a hypodermis that is morphologically very different from the blubber (Rosa, 2006).…”