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Spined pygmy shark
The spined pygmy shark (''Squaliolus laticaudus'') is a species of dogfish shark in the family Dalatiidae found widely in all oceans. Growing no larger than approximately , it is one of the smallest sharks alive, with this record beaten by the dwarf lanternshark. This shark has a slender, cigar-shaped body with a sizable conical snout, a long but low second dorsal fin, and an almost symmetrical caudal fin. It and its sister species ''S. aliae'' are the only sharks with a spine on the first dorsal fin and not the second. Spined pygmy sharks are dark brown to black, with numerous bioluminescent organs called photophores on their ventral surface. The shark is believed to use these photophores to match ambient light conditions, which break up its silhouette and help the shark to avoid being seen by predators.
Usually inhabiting nutrient-rich waters over upper continental and insular slopes, the spined pygmy shark feeds on small bony fishes and squid. Like its prey it is a diel vertical migrator, spending the day at close to deep and moving towards a depth of at night. Reproduction is presumably aplacental viviparous, with female giving birth to litters of 4 pups. This diminutive shark has no economic value. The International Union for Conservation of Nature (IUCN) has assessed this species as of Least Concern, as it faces little threat from commercial fisheries and has a wide distribution.
==Taxonomy and phylogeny==
The spined pygmy shark was one of many new species discovered during the course of the 1907–1910 Philippine Expedition of the U.S. Fish Commission Steamer ''Albatross''. It was described by American ichthyologists Hugh McCormick Smith and Lewis Radcliffe in a 1912 paper for the scientific journal ''Proceedings of the United States National Museum'', based on two specimens collected in Batangas Bay, south of Luzon in the Philippines. One of these, a long adult male, was designated the type specimen.
Smith and Radcliffe coined the new genus ''Squaliolus'' for this shark, and gave it the specific epithet ''laticaudus'', from the Latin ''latus'' meaning "broad" or "wide", and ''cauda'' meaning "tail". The spined pygmy shark may also be referred to as the dwarf shark or the bigeye dwarf shark.〔 Based on similarities in their claspers (male intromittent organs), the closest relative of the spined pygmy shark and the related ''S. aliae'' is thought to be the pygmy shark (''Euprotomicrus bispinatus'').
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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