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False catshark
The false catshark or sofa shark (''Pseudotriakis microdon'') is a species of ground shark in the family Pseudotriakidae, and the sole member of its genus. It has a worldwide distribution, and has most commonly been recorded close to the bottom over continental and insular slopes, at depths of . Reaching in length, this heavy-bodied shark can be readily identified by its elongated, keel-like first dorsal fin. It has long, narrow eyes and a large mouth filled with numerous tiny teeth. It is usually dark brown in color, though a few are light gray.
With flabby muscles and a large oily liver, the false catshark is a slow-moving predator and scavenger of a variety of fishes and invertebrates. It has a viviparous mode of reproduction, featuring an unusual form of oophagy in which the developing embryos consume ova or egg fragments released by the mother and use the yolk material to replenish their external yolk sacs for later use. This species typically gives birth to two pups at a time. The International Union for Conservation of Nature (IUCN) presently lacks sufficient data to assess the conservation status of the false catshark. While neither targeted by fisheries nor commercially valuable, it is caught incidentally by longlines and bottom trawls, and its low reproductive rate may render it susceptible to population depletion.
==Taxonomy and phylogeny==
The false catshark was first described by Portuguese ichthyologist Félix de Brito Capelo in the ''Jornal do Sciências Mathemáticas, Physicas e Naturaes'' in 1868. He based his account on a long adult male caught off Setubal, Portugal.〔 Brito Capelo thought the specimen resembled a member of the genus ''Triakis'', except lacking a nictitating membrane (though it is now known that this species does in fact have this trait). Thus, he assigned it to the new genus ''Pseudotriakis'', from the Greek ''pseudo'' ("false"). At the time, ''Triakis'' was classified with the catsharks, hence "false catshark". The specific name ''microdon'' comes from the Greek ''mikros'' ("small") and ''odontos'' ("tooth").〔 Other common names for this species are dumb shark (from its Japanese name ''oshizame'') and keel-dorsal shark.〔〔
Pacific populations of the false catshark were once regarded as a separate species, ''P. acrales''. However, morphological comparisons have failed to find any consistent differences between ''P. microdon'' and ''P. acrales'', leading to the conclusion that there is only one species of false catshark.〔〔 The closest relatives of the false catshark are the gollumsharks (''Gollum''). ''Pseudotriakis'' and ''Gollum'' share a number of morphological similarities.〔 Phylogenetic analysis using protein-coding genes has found that the amount of genetic divergence between these taxa is less than that between some other shark species within the same genus. This result suggests that the many autapomorphies (unique traits) of the false catshark evolved relatively recently, and supports the grouping of ''Pseudotriakis'' and ''Gollum'' together in the family Pseudotriakidae.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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