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Spiny dogfish
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<p>The spiny dogfish (<i>Squalus acanthias</i>), spurdog, mud shark, or piked dogfish is one of the best known <a href="/facts/Species/oDg6b96r">species</a> of the <a href="/facts/Squalidae/pthXYVsM">Squalidae</a> (dogfish) <a href="/facts/Family_(biology)/qTrn6E8E">family</a> of <a href="/facts/Shark/rh5Cotvx">sharks</a>, which is part of the <a href="/facts/Squaliformes/aPjJxtbk">Squaliformes</a> order. </p><p>While these common names may apply to several species, <i>Squalus acanthias</i> is distinguished by two spines (one anterior to each <a href="/facts/Dorsal_fin/zAPuxI1G">dorsal fin</a>) and no <a href="/facts/Anal_fin/kS10PMPf">anal fin</a>. It lives in shallow waters and further offshore in most parts of the world, especially in temperate waters. Those in the northern Pacific Ocean were reevaluated in 2010 and found to constitute a separate species, now called the <a href="/facts/Pacific_spiny_dogfish/LH4sGyNt">Pacific spiny dogfish (<i>Squalus suckleyi</i>)</a>. </p>