Squalus Artedi, 1738: 504 (description); Linnaeus, 1758: 233 (original description; “Oceano Europaeo”); Molina, 1782: 188, 189 (listed; Chile); Rafinesque, 1810: 45 (listed; Sicily); Girard, 1855 (listed; Chile); Gill, 1862: 367–405 (in classification); Poey, 1868: 211, 213, 454 (listed; Cuba); Berg, 1895: 5, 6 (listed; Argentina and Uruguay); Jordan & Evermann, 1898: 53, fig. 24 (listed; North and Central America); Schreiner & Ribeiro, 1903: 79 (listed; Brazil); Jordan, 1907: 202 (cited); Miranda Ribeiro, 1907: 167, 168 (listed; Brazil); Regan, 1908: 39, 45, 48 (identification key, listed; global); Garman, 1913: 191 (description; global); Miranda Ribeiro, 1923 (listed; Brazil); Howell-Rivero, 1936: 45 (revision; Cuba); Fowler, 1936: 69–71 (description; Western Africa); Fowler, 1941: 129 (listed; Brazil); Bigelow & Schroeder, 1948: 451–480, figs 87–90 (revision; Northwestern Atlantic); Bigelow, Schroeder & Springer, 1953: 220–222 (cited; Western Atlantic); Bigelow & Schroeder, 1957: 26–37, figs 3, 4 (description); Ledoux, 1970, 65– 69 (revision; Mediterranean Sea); Bass et al., 1976 (revision; Eastern South Africa); Figueiredo, 1977: 8 (listed; Southeastern Brazil); Cadenat & Blache, 1981: 46–52; figs 28–31 (revision; Mediterranean Sea, North Atlantic Ocean); Figueiredo, 1981: 17 (listed; Brazil); Lucena & Lucena, 1981: 2–4 (listed; Brazil); Compagno, 1984: 109–123 (revision; global); Kondyurin & Myagkov, 1984: 118–120, (revision; Western Atlantic); Menni et al., 1984: 62, 83, 84 (listed; Argentina and Uruguay); Myagkov & Kondyurin, 1986: 1–20 (revision; Atlantic); Muñoz-Chápuli & Ramos, 1989 (revision; Eastern Atlantic); Gadig & Moreira, 1992: 112, 118 (cited; Brazil); Calderón, 1994 (cited; Brazil); Marques, 1994 (description; Brazil); Gomes et al., 1997: 93–98 (listed, description; Brazil); Cervigón & Alcal, 1999: 122 (revision; Venezuela); Compagno & Niem, 1999: 1229–1232 (revision; Western-Central Pacific); Lessa et al., 1999 (cited, listed; Brazil); Marques, 1999 (description; Brazil); Mazzoleni & Schwingel, 1999: 114 (listed; South Brazil); Gadig et al., 2000: 129 (cited; Cear, Brazil); Gadig, 2001: 54–59 (revision; Brazil); Soto, 2001: 94–96 (listed; Brazil); Compagno, 2002: 380–385 (revision; Western Central Atlantic); Nion et al., 2002: 4, 65 (listed; Uruguay); Haimovici et al., 2003 (cited; Brazil); Meneses & Paesch, 2003: 7, 8, 25 (listed; Uruguay, Argentina); Heemstra & Heemstra, 2004 (cited, Southern Africa): 49, 53– 54; Soto & Mincarone, 2004: 73–82 (listed; Brazil); Compagno et al., 2005: 72 (description; global); Haddad & Gadig, 2005 (cited; Brazil); Lamilla & Bustamante, 2005: 9, 26 (cited; Chile); Hazin et al., 2006 (cited; Northeastern Brazil); Jablonski et al., 2006 (cited; Brazil); Nelson, 2006: 66 (listed; global); Last et al., 2007 (revision; Australia); Louro & Rossi- Wongtschowski, 2007 (cited; Brazil); Menni & Lucifora, 2007: 2, 3 (listed; Argentina, Uruguay); Pon & Gandini, 2007 (cited; Argentina); Carrier et al., 2010: 44, 127, 139 (cited); Gomes et al., 2010: 44, 45 (cited; Brazil); Menni et al., 2010 (cited; Southwestern Atlantic); Saéz et al., 2010: 623, 624 (identification key; Chile); Tomás et al., 2010 (cited; Brazil); Viana, 2011: 1–373 (description; Southwestern Atlantic); Eschmeyer & Fricke, 2015 (listed; global); Bornatowski & Abilhoa, 2012: 35 (cited; Brazil); Rosa & Gadig, 2014: 92, 97 (listed, cited; Brazil).
Acanthorhinus Blainville, 1816: 121 (original description, not illustrated); Fowler, 1936: 61 (cited); Bigelow & Schroeder, 1948: 452 (cited).
Spinax: Cuvier, 1817: 130 (cited); Cuvier, 1863: 320 (listed).
Acanthias Risso, 1826: 131 (original description, not illustrated; Mediterranean Sea); Müller & Henle, 1841: 83 (listed); Gill, 1861: 60 (listed; North and Central America; used Squalus for Carcharhinus in this work); Duméril, 1865: 435, 436 (description); Günther, 1866: 384, 396 (listed; Central America); Vaillant, 1888: 7 (cited; Argentina).
Type species: Squalus acanthias Linnaeus, 1758 by subsequent designation of Gill (1862: 405).
Diagnosis. Squalus is characterized by the following combination of characters: slender and fusiform body, arched dorsally at anterior region; lateral keels restricted to caudal peduncle; short snout, rounded or obtuse at the tip; anterior nasal flaps lobe-like, however without forming nasal barbels; presence of slender dorsal spines without lateral grooves prior to each dorsal fin, extending or not to the apex of corresponding fin; second dorsal fin considerably smaller and more raked than first dorsal fin; caudal peduncle with conspicuous upper and lower precaudal pits; asymmetric caudal fin without subterminal notch; dorsal caudal lobe considerably greater in length than ventral caudal lobe; teeth unicuspid, small, similar in both jaws with short, slightly oblique cusps; dermal denticles unicuspid or tricuspid.
Squalus is distinguished from Cirrhigaleus in having anterior nasal flaps with short secondary lobe without forming nasal barbels (vs. secondary lobe very elongated and forming nasal barbels extending to anterior margin of mouth), second dorsal fin smaller and lower than first dorsal fin (vs. dorsal fins of similar length and height with second dorsal fin as high and large as first dorsal fin), second dorsal-fin spine larger in length than first dorsal-fin spine (vs. second dorsal-fin spine equal in length to first dorsal-fin spine), and conspicuous upper and lower precaudal pits (vs. absence of lower precaudal pit). It is further differentiated from Cirrhigaleus by having narrow dermal denticles (vs. denticles conspicuously broad), and body fusiform and somewhat arched dorsally throughout all of its length (vs. body robust and markedly humped dorsally).