Placoid Scale Types and Their Distribution in Squalus Acanthias

Sayles, Leonard P.; Hershkowitz, S.

doi:10.2307/1537869

Cited by 9 publications

(3 citation statements)

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“…In elasmobranchs, elastin fibers may be dispersed among the collagen fibers of the dermal layers (Naresh et al,1985,1997). Situated upon this pressurized exoskeleton of collagenous dermal fibers (Wainwright et al,1978; Martinez et al,2002), the placoid scales are found in a variety of shapes and sizes that vary both interspecifically and even across the body of perhaps all species of sharks (Sayles and Hershkowitz,1937; Bigelow and Schroeder,1948; Reif,1985a; Raschi and Tabit,1992; Bargar and Thorson,1995; Deynat,2005).…”

Section: Introductionmentioning

confidence: 99%

Scale morphology and flexibility in the shortfin mako Isurus oxyrinchus and the blacktip shark Carcharhinus limbatus

Motta

Habegger

Lang

et al. 2012

Journal of Morphology

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We quantified placoid scale morphology and flexibility in the shortfin mako Isurus oxyrinchus and the blacktip shark Carcharhinus limbatus. The shortfin mako shark has shorter scales than the blacktip shark. The majority of the shortfin mako shark scales have three longitudinal riblets with narrow spacing and shallow grooves. In comparison, the blacktip shark scales have five to seven longitudinal riblets with wider spacing and deeper grooves. Manual manipulation of the scales at 16 regions on the body and fins revealed a range of scale flexibility, from regions of nonerectable scales such as on the leading edge of the fins to highly erectable scales along the flank of the shortfin mako shark body. The flank scales of the shortfin mako shark can be erected to a greater angle than the flank scales of the blacktip shark. The shortfin mako shark has a region of highly flexible scales on the lateral flank that can be erected to at least 50°. The scales of the two species are anchored in the stratum laxum of the dermis. The attachment fibers of the scales in both species appear to be almost exclusively collagen, with elastin fibers visible in the stratum laxum of both species. The most erectable scales of the shortfin mako shark have long crowns and relatively short bases that are wider than long. The combination of a long crown length to short base length facilitates pivoting of the scales. Erection of flank scales and resulting drag reduction is hypothesized to be passively driven by localized flow patterns over the skin. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.

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Section: Introductionmentioning

confidence: 99%

Scale morphology and flexibility in the shortfin mako Isurus oxyrinchus and the blacktip shark Carcharhinus limbatus

Motta

Habegger

Lang

et al. 2012

Journal of Morphology

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“…To be efficient, these denticles need to overlap each other forming a continuous surface with ridges [20]. Therefore, Massive Tabular Denticles (MTD) and Massive Lanceolate Denticles (MLD) groups would likely serve to protect tissues from abrasion or ectoparasites such as denticles observed in the central oral cavity of the longtailed carpet shark, Hemiscyllium ocellatum [20,39] or near the snout of the spiny dogfish, Squalus acanthias [40]. Denticles from the dorsal side and the pectoral fins possess well-defined ridges on their surface that may also improve hydrodynamism.…”

Section: Discussionmentioning

confidence: 99%

The megamouth shark, Megachasma pelagios, is not a luminous species

et al. 2020

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Despite its five meters length, the megamouth shark (Megachasma pelagios Taylor, Compagno & Struhsaker, 1983) is one of the rarest big sharks known in the world (117 specimens observed and documented so far). This filter-feeding shark has been assumed to be a luminous species, using its species-specific white band to produce bioluminescence as a lure trap. Another hypothesis was the use of the white band reflectivity to attract prey or for social recognition purposes. However, no histological study has ever been performed to confirm these assumptions so far. Two hypotheses about the megamouth shark's luminescence arose: firstly, the light emission may be intrinsically or extrinsically produced by specific light organs (photophores) located either on the upper jaw white band or inside the mouth; secondly, the luminous appearance might be a consequence of the reflection of prey luminescence on the white band during feeding events. Aims of the study were to test these hypotheses by highlighting the potential presence of specific photophores responsible for bioluminescence and to reveal and analyze the presence of specialized light-reflective structures in and around the mouth of the shark. By using different histological approaches (histological sections, fluorescent in situ hybridization, scanning electron microscopy) and spectrophotometry, this study allows to unravel these hypotheses and strongly supports that the megamouth shark does not emit bioluminescence, but might rather reflect the light produced by bioluminescent planktonic preys, thanks to the denticles of the white band.

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“…Information on the presence of body denticles or placoid scales in sharks has been widely reported in the scientific literature on elasmobranchs. Studies that focus on oral denticles are scarce, but their presence in the oral cavity of Elasmobranchs, as well as in other segments of the digestive system and gill arches is a known fact since the late 19 th century (Hertwig, ; Mello et al, ; Sayles and Hershkowitz, ).…”

Section: Discussionmentioning

confidence: 99%

Ultrastructure of dermal denticles in sharpnose shark (Rhizoprionodon lalandii) (Elasmobranchii, Carcharhinidae)

Laranjeira

Guimarães

Amorim

et al. 2015

Microscopy Res & Technique

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The presence of denticles in the external surface, oral cavity, fins, and clasper of Elasmobranchii has been widely reported. These structures, called body denticles, may be observed on the body surface of sharks. Dermal and oral denticles are made up by a basal plate that is embedded in the dermis, forming a peduncle that grows from the base to the crown. These denticles may protect the skin against abrasion, and improve hydrodynamics and gill arches function. Rhizoprionodon lalandii is a widely distributed and very common species in Brazilian coastal areas. The aims of this study was to compare the morphology of oral and body denticles of R. lalandii to understand the implications of these structures in the behavior of these animals. Morphological analysis showed that there are differences between dermal and oral denticles, which are related to their role in different body regions. Body denticles have three cusps, and well-defined crests and ridges, and literature data suggest that suggest that hydrodynamics is their main function. Most of the oral denticles have only one cusp, and their morphology and distribution showed that their main functions are preparing food to be swallowed and protecting the oral cavity against abrasion.

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Placoid Scale Types and Their Distribution in Squalus Acanthias

Cited by 9 publications

References 1 publication

Scale morphology and flexibility in the shortfin mako Isurus oxyrinchus and the blacktip shark Carcharhinus limbatus

Scale morphology and flexibility in the shortfin mako Isurus oxyrinchus and the blacktip shark Carcharhinus limbatus

The megamouth shark, Megachasma pelagios, is not a luminous species

Ultrastructure of dermal denticles in sharpnose shark (Rhizoprionodon lalandii) (Elasmobranchii, Carcharhinidae)

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