Vergleichende Histologie der Haut

Basics of skin structure and function in elasmobranchs: a review

“…Moreover, many polygonal cells of weak cytoplasmic staining intensities within the lower or middle parts of the stratum spinosum can be regarded as developing holocrine secretory cells. Nevertheless, in rays, the number of secretory cells is clearly lower, especially in species groups with a keratized stratum superficiale (Koecke, 1968; Whitear, 1986 a ; Whitear & Moate, 1998; Seegers & Meyer, 2009). The number of secretory cells per unit area is not known, but findings from S. canicula demonstrated 40 secretory cells per 100 basal cells in the dorsal region, and only 20 secretory cells in the front region and the fins.…”

“…In this way, a better stabilization and protection of the body was made possible, but the extent of mineralization was again reduced during further evolution, independent of the fish group, thus improving, as in the teleosts, locomotion qualities which are vital for predator and prey. In the Chondrichthyes such development can also be detected, but although mineralization possibilities here have been lost to a greater extent, they are still used not only to stabilize the vertebral column but also primarily to rather continuously produce the typical scales (Koecke, 1968; Giersberg & Rietschel, 1979; Whitear, 1986 b ; Meyer et al, 1989; Meyer, 1993; Grogan & Lund, 2004; Seegers & Meyer, 2009). Generally, it can be assumed that specific evolutionary trends are involved, such as the fact that the acquisition of 1,25‐dihydroxyvitamin D 3 receptor by certain neural‐crest cells during the evolution of different vertebrate groups greatly influenced the functional type of dermal mechanical support.…”

“…During fast swimming an increase in hydrostatic pressure is exerted against the skin and the body remains stiff and can store more energy when the shark swims faster. Thus, the integument of sharks, particularly, and also of some teleosts, acts as an exoskeleton‐like total‐body tendon in parallel with the muscles, considering that such a structural system mechanically has a more favourable effect on the transfer of muscle contractions than on the standard connection with the vertebral column (Rabl, 1931; Koecke, 1968; Moss, 1972; Wainwright et al , 1978; Hebrank, 1980; Whitear, 1986 b ; Meyer et al, 1989; Seegers & Meyer, 2009). In rays, such specific structure is restricted to the dorsal body region including the tail; in the ventral body region, the collagen fibre bundles of the stratum compactum appear rather thin and loose, and especially in the lower dermal parts of the long pectoral fin, groups of thin cartilaginous radials are observable [Fig.…”

“…Nevertheless, placoid scales are not of ancient scale type, but a very modern one that forms the dentition in the present sharks and rays, and enables sharks, in particular, to develop new teeth throughout life. Therefore, placoid scales are not precursors or the preliminary stages of teeth in higher vertebrates (van Oosten, 1957; Koecke, 1968; Giersberg & Rietschel, 1979; Kemp, 1999; Seegers & Meyer, 2009).…”

“… Basics of the mechanosensory lateral‐line system in sharks and rays: (a) for sharks visible by a tubule contacting the main lateral canal with (b) a cupula‐covered neuromast and (c) the distribution of lateral line canals as shown in Gymnura micrura . (a) Modified from Koecke (1968) with kind permission from Springer Science and Business Media B.V; (b) modified from Maruska (2001) with kind permission from Springer Science and Business Media B.V. D, dermis; HYO, hyomandibular canal; IO, infraorbital canal; LC, main lateral‐line canal; MAN, mandibular canal; N, nerve; NF, nerve fibres; NM, neuromast; NMC, neuromast cupula; PPL, posterior lateral line canal; SC, scapular canal; SO, supraorbital canal; SPL, subpleural loop; Tu, tubule. …”