Microscopic aspects of the nictitating membrane in Carcharhinidae and Sphyrnidae sharks: a preliminary study

Poscai, Aline Nayara; Rangel, Bianca de Sousa; Casas, André Luis da Silva; Wosnick, Natascha; Rodrigues, Alexandre; Rici, Rose Elí Grassi; Kfoury, José Roberto

doi:10.1007/s00435-017-0351-1

Cited by 12 publications

(12 citation statements)

References 18 publications

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“…role in eye protection [3]. Though the overall morphologies of the denticles in the nictitating membranes of carcharhinid and sphyrnid sharks are different from those of whale sharks, they both have especially thick denticle crowns, which suggests that they have a similar function of mechanical protection.…”

Section: Plos Onementioning

confidence: 99%

“…For example, carcharhinid and sphyrnid sharks have nictitating membranes or "third eyelids", which cover their eyes completely during their feeding activities [2]. The outer surface of this membrane is covered with dermal denticles, which likely increases its protective ability [3]. In contrast, many other elasmobranchs that are not equipped with nictitating membranes have to protect their eyes in different ways, such as retracting the eyeballs into the head (e.g., electric ray [4]; guitarfish [5]), or rotating the eyeballs back into the orbit (e.g., white shark [6]).…”

Section: Introductionmentioning

confidence: 99%

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Armored eyes of the whale shark

et al. 2020

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This report elaborates on adaptations of the eyes of the whale shark Rhincodon typus (Elasmobranchii, Rhincodontidae), including the discovery that they are covered with dermal denticles, which is a novel mechanism of eye protection in vertebrates. The eye denticle differs in morphology from that of the dermal denticles distributed over the rest of the body, consistent with a different function (abrasion resistance). We also demonstrate that the whale shark has a strong ability to retract the eyeball into the eye socket. The retraction distance was calculated to be approximately half the diameter of the eye, which is comparable to those of other vertebrates that are known to have highly retractable eyes. These highly protective features of the whale shark eye seem to emphasize the importance of vision for environmental perception, which contradicts the general, though poorly established, notion of low reliance on vision in this species.

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Section: Plos Onementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Armored eyes of the whale shark

et al. 2020

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“…The nictitating membrane, found exclusively in carcharhiniform sharks, evolved as an extension of the lower eyelid and is thought to be similar to that found in amphibians, birds and mammals. Comprised of dense connective tissue covered in denticles (placoid scales), the nictitating membrane is a mobile component of the ocular adnexa, which is well developed in at least four families of sharks including the family Carcharhinidae (Figure G). During feeding, sharks close the nictitating membrane and open the jaw at the same time, showing a close relation between prey capture and eye protection.…”

Section: The Cornea and Nictitating Membranementioning

confidence: 99%

“…During feeding, sharks close the nictitating membrane and open the jaw at the same time, showing a close relation between prey capture and eye protection. Inter‐specific differences in the hexagonal arrangement of dermal denticles over the membrane suggest dynamic and biomechanical adaptation of this highly mobile structure to rapidly and efficiently protect against abrasion, mainly during predation events …”

Section: The Cornea and Nictitating Membranementioning

confidence: 99%

Scene through the eyes of an apex predator: a comparative analysis of the shark visual system

Collin

2018

Clinical and Experimental Optometry

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The eyes of apex predators, such as the shark, have fascinated comparative visual neuroscientists for hundreds of years with respect to how they perceive the dark depths of their ocean realm or the visual scene in search of prey. As the earliest representatives of the first stage in the evolution of jawed vertebrates, sharks have an important role to play in our understanding of the evolution of the vertebrate eye, including that of humans. This comprehensive review covers the structure and function of all the major ocular components in sharks and how they are adapted to a range of underwater light environments. A comparative approach is used to identify: species-specific diversity in the perception of clear optical images; photoreception for various visual behaviours; the trade-off between image resolution and sensitivity; and visual processing under a range of levels of illumination. The application of this knowledge is also discussed with respect to the conservation of this important group of cartilaginous fishes.

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“…Some particularities of the denticles that make them interesting tools include: (a) their morphological aspects (i.e., shape, size, and arrangement) are highly variable intra and interspecifically; (b) they are correlated with shark ecology; (c) are very abundant across the body of sharks, including oral regions and nictitating membrane; and (d) are continually exchanged (e.g., Dillon et al, ; Poscai et al, ; Rangel et al, ). Although recent studies have addressed extensively about morphology, taxonomy, and function of denticles (e.g., Dillon et al, ), more studies are needed considering both the high shark diversity (~500 living species; Weigmann, ) and intra and interspecifically variability of denticles across the body and oral cavity (e.g., Ankhelyi, Wainwright, & Lauder, ; Dillon et al, ; Rangel, Salmon, Poscai, Kfoury Jr., & Rici, ).…”

Section: Introductionmentioning

confidence: 99%

Microstructural morphology of dermal and oral denticles of the sharpnose sevengill shark Heptranchias perlo (Elasmobranchii: Hexanchidae), a deep‐water species

Rangel

Amorim

Kfoury

et al. 2019

Microscopy Res & Technique

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The dermal denticles are among the unique morphological adaptations of sharks, which have been acquired throughout their long evolutionary process of more than 400 million years. Species‐specific morphological characteristics of these structures has been applied specially as tools for functional and taxonomic (family‐level) studies. Nevertheless, few studies have explored the diversity of denticle structure in different around the body and oral cavity. In the present study, we described the morphological differences observed in skin and oral cavity of sharpnose sevengill shark Heptranchias perlo, using scanning electron microscopy. Our findings demonstrate substantial variation in morphological structure of the denticles of the body and oral cavity. Overall, the dermal denticles observed across body surface were overlapped, tricuspid, with the central cuspid being more pronounced, pointed, and triangular in shape compared with lateral ones. Unlike, the denticles on the tip of the nose had a smooth crown, with rounded edges, being compact, and overlapped. The oral denticles were found in the ventral and dorsal region of the oral cavity. They also were tricuspid, but with differences in arrangement and ridges. These results suggest a strict functional relationship with the morphological characteristics observed. Such morphological diversity body‐region‐dependent highlights the need for comparative studies that include oral denticles, since this structure has an important functional role in sharks and can be found in fossil and recent records.

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Microscopic aspects of the nictitating membrane in Carcharhinidae and Sphyrnidae sharks: a preliminary study

Cited by 12 publications

References 18 publications

Armored eyes of the whale shark

Armored eyes of the whale shark

Scene through the eyes of an apex predator: a comparative analysis of the shark visual system

Microstructural morphology of dermal and oral denticles of the sharpnose sevengill shark Heptranchias perlo (Elasmobranchii: Hexanchidae), a deep‐water species

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