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The spiny dogfish, spurdog, mud shark, or piked dogfish, ''Squalus acanthias'', is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order. While these common names may apply to several species, ''Squalus acanthias'' is distinguished by having two spines (one anterior to each dorsal fin) and lacks an anal fin. It is found mostly in shallow waters and further offshore in most parts of the world, especially in temperate waters. ==Morphology and behavior== The spiny dogfish has dorsal spines, no anal fin, and white spots along its back. The caudal fin has asymmetrical lobes, forming a heterocercal tail. The species name ''acanthias'' refers to the shark's two spines. These are used defensively. If captured, the shark can arch its back to pierce its captor. Glands at the base of the spines secrete a mild venom. Males mature at around 11 years of age, growing to in length; females mature in 18–21 years and are slightly larger than males, reaching . Both sexes are greyish brown in color and are countershaded. Males are identified by a pair of pelvic fins modified as sperm-transfer organs, or "claspers". The male inserts one clasper into the female cloaca during copulation. Reproduction is aplacental viviparous, which was before called ovoviviparity. Fertilization is internal. The male inserts one clasper into the female oviduct orifice and injects sperm along a groove on the clasper's dorsal section. Immediately following fertilization, the eggs are surrounded by thin shells called "candles" with one candle usually surrounding several eggs. Mating takes place in the winter months with gestation lasting 22–24 months. Litters range between 2 and 11 but average 6 or 7. Spiny dogfish are bottom-dwellers They are commonly found at depths of around 50-149m, but have been found deeper than 700m. Life span is estimated to be more than 100 years and their gestation period is 18 to 24 months, which may be the longest of any known animal.〔(Spiny dogfish ). Memorandum of Understanding on the Conservation of Migratory Sharks.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spiny dogfish」の詳細全文を読む スポンサード リンク
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