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Abstract
Despite its 5 meters long, the megamouth shark (Megachasma pelagios) is one of the rarest types of sharks known in the world recently discovered in 1983 (only 54 specimens observed and documented so far). This filter shark has been described many times as possessing a luminous mouth used as a lure trap or for social recognition. However, none histological study has been realized to confirm these assumptions so far. Two hypotheses about the light production arose notably from video recording observations: (i) the light may be produced by bioluminescence inside its mouth or on the white band of its upper jaw; (ii) light can be due to the reflection on this white band. Given the fact that we had the opportunity to analyze mouth tissues from one individual, the aim of the current study is to test these hypotheses by highlighting the presence of light organs (photophores) or specialized light-reflective structures. Up to now, the study of skin tissues from 11 sites (8 around and inside the mouth, 3 control sites: on the back, the belly and the pectoral fins) performed thanks to several techniques (histological sections, CT-scan, microradiographies, SEM, cryofractures and spectrophotometer) do not indicate the presence of any photophores. However, dermal denticles (calcified structures on shark skin) embedded into the white band are likely involved in reflection of light. Still, the observation of a living individual and the study of fresh or well-fixed and conserved tissues are essential to determine if this shark is bioluminescent and to confirm if it is able to reflect light.
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Moris, V., Behets Wydemans, C., Claes, J., & Mallefet, J. (2014). Light on skin properties of megamouth shark, Megachasma pelagios (Lamniforme). In Royal Belgian Zoological Society (RBZS) (ed.), ZOOLOGY 2014 (p. p. 210). https://hdl.handle.net/2078.5/187548