Friday 1 January 2016

Mollisquama sp.: A Pocket Shark from the Gulf of Mexico.

In 1984 the Russian ichthyologist Vladamir Dolganov described an unusual Dalatid Shark (the group which also includes Cookie Cutter Sharks, Kitefin Sharks and Taillight Sharks) from the Professor Mesyatzev Seamount on the Nazca Ridge of the southeast Pacific Ocean. This was 40 cm in length and had a distinctive pocket-shaped gland above the pectoral fin, earning it the common name 'Pocket Shark' (Mollisquama parini). However no further specimens of this Shark were found in the South Pacific, and the species remains somewhat of a mystery.

In a paper published in the journal Zootaxa on 22 April 2015, Mark Grace of the Mississippi Laboratories of the Southeast Fisheries Science Center, Michael Doosey and Henry Bart of the Tulane University Biodiversity Research Institute and Gavin Naylor of the Hollings Marine Laboratory describe a second specimen of Mollisquama from the Gulf of Mexico.

The new specimen is considerably smaller than the original, at 14.2 cm, with a head considerably larger in proportion to the body, though this may represent a different growth stage (most animals change their proportions as they grow). It is also male rather than female, and shows a number of features not seen on the first specimen, most notably a series of photophores (bioluminescent organs) and a distinctive circular dermal denticle (the scales of Sharks are structurally similar to the teeth of other vertebrates, and are therefore called dermal denticles) behind the lower jaw. This makes it quite likely that the Gulf of Mexico specimen is a different species to the South Pacific specimen, however since Grace et al. were not able to inspect the original specimen the refrain from describing it as such until this becomes possible.

Mollisquama sp., Gulf of Mexico specimen in lateral view. Grace et al. (2015).

See also... tagging Whale Sharks in the Red Sea                                                                                  Whale Sharks (Rhincodon typus) are the largest extant Shark species, and indeed the largest living... new species of Sawshark from the Philippines.                                            Sawsharks (Pristiophoridae) are highly specialized Sharks related to... species of Catshark from the Galapaagos.                                           Catsharks, or Dogfish, are small bottom dwelling sharks found in oceans throughout the world.
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