Author: Linck, 1790
Field Marks:
Usually slender houndsharks with long, parabolic subangular snouts, dorsolateral eyes and strong subocular ridges, angular mouths, teeth formed into a pavement, with cusps and cusplets variably developed but usually obsolete or absentj medial teeth not differentiated from anterolaterals, and second dorsal fin nearly as large as first.
Diagnostic Features:
Snout long and parabolic-subangular in dorsoventral view, preoral length less than 1.3 times the mouth width; eyes horizontally elongated or oval and dorsolateral, subocular ridges strong; anterior nasal flaps rather elongated and lobate, well separated from each other and mouth; no nasoral grooves; internarial width about 1 to 2 times the nostril width; mouth angular and moderately long; labial furrows moderately long, uppers falling well behind level of upper symphysis; teeth not bladelike and similar in both jaws, varying from somewhat compressed and with short erect cusps and cusplets to rounded, molariform, and without cusps and cusplets; medial teeth not differentiated from anteroposteriors. First dorsal fin moderately large, its base less than 3/4 of dorsal caudal margin, its origin over pectoral inner margins or slightly behind their free rear tips, its midbase about equidistant between pectoral and pelvic bases or closer to pectoral bases; second dorsal nearly as large as first, its height about 2/3 to 3/4 as high as first; anal fin considerably smaller than second dorsal; ventral caudal lobe hardly developed in young but varying from poorly developed to short and strong in adults; terminal lobe of caudal fin moderately long and about 2.3 to 3 times in dorsal caudal margin.
Remarks:
The arrangement of this genus is based on Heemstra's (1973, pers.comm.) revisions, from which much information on nomenclature, range, and size are taken. When preparing the account of Mustelus at the J.L.B. Smith Institute of Ichthyology, the author was able to freely utilize the knowledge and unpublished data of Dr P.C. Heemstra, for which he is very grateful; the writer suspects that the present section would have been far poorer without this help and information. Dr Heemstra intends to publish an updated version of his 1973 revision of the genus, in which five new species will be described, two in the western Atlantic, two in the tropical eastern Pacific, and one in tropical Australian waters (not sympatric with Mustelus antarcticus). Revisionary works by Springer (1939), Bigelow and Schroeder (1940, 1948), and Kato, Springer and Wagner (1967) were also utilized.
The species of Mustelus (smooth-hounds, emissoles, palombos, tollos, gummy sharks, etc.) are abundant temperate to tropical, inshore bottom-dwelling sharks that figure prominently in artisanal and inshore commercial fisheries.
There have been a number of attempts to divide or subdivide Mustelus on mode of reproduction, but these have in general run afoul of the formerly confused generic nomenclature and of lack of knowledge on the reproduction of quite a number of species. Mustelus species are ovoviviparous (aplacental viviparous) or viviparous (placental viviparous or placentoviviparous), but it is not known if placental species have evolved more than once within the genus or if the aplacental species have secondarily evolved from placental species. If ovoviviparity is primitive within Mustelus, viviparity in the genus has evolved separately from that in other carcharhinoids. For further discussion of the taxonomic and nomenclatural aspects of reproduction in Mustelus, see Heemstra (1973) and Compagno (1979).
The genus Allomycter was described by Guitart (1972) for a species, A. dissutus, known only from photographs (type specimen lost). This was tentatively recognized by Compagno r973b) but photographs of the species supplied later by Dr D. Guitart suggested that it was based on a Mustelus (probably M. canis) with an abnormal, possibly damaged or teratological snout (see Heemstra (1973) and Compagno (1979) for further discussion).
There has been considerable difficulty in the past with separating this genus from Triakis. See Kato (1968), Heemstra (1973), Bass, D'Aubrey and Kistnasamy (1975b), but especially Compagno (1970, 1973b, 1979) for discussion of this problem and its resolution.
Members of the genus Mustelus are unusually difficult to separate from one another, particularly without the use of internal characters. Many of the morphological, morphometric and meristic characters that distinguish species partially overlap and considerable variation occurs within species. As Mustelus species have limited geographic distributions a tentative identification of Mustelus lunulatus from, say, the western North Pacific is probably not that species but another, perhaps M. griseus. See Heemstra (1973) for regional keys to species.