Atlantic Lobefin Dogfish

description

Description. External morphology. Measurements and meristic data are summarized in Tables 5 – 6. Body fusiform, slender and depressed through, with head height 0.9 (0.8 – 1.3) times trunk height and 1.0 (0.8 – 1.2) times abdomen height; greatest width of body at head with head width 1.3 (1.0 – 1.3) times trunk width and 1.6 (1.2 – 1.7) times abdomen width. Head flattened dorsally and elongate, its length 22.7 % (21.5 % – 24.3 % TL); head broader at mouth than at nostrils (width at mouth 12.2 %, 9.7 % – 12.2 % TL vs. width at nostrils 7.5 %, 6.3 % – 7.4 % TL). Snout very large (preorbital length 7.9 %, 7.0 % – 7.9 % TL), obtuse and rounded at tip; anterior margin of nostrils strongly bilobate, positioned more laterally; prenarial length 1.2 (1.0 – 1.2) times distance from nostril to upper labial furrow; prenarial length 1.3 (1.1 – 1.4) times eye length; internarial space 1.1 (0.9 – 1.5) times eye length. Eyes oval, placed laterally closer to the snout tip than first gill slit, with anterior margin convex and posterior margin notched; eyes enlarged, their length 2.3 (1.7 – 2.9) times their height. Prespiracular length 1.6 (1.6 – 1.7) times preorbital length. Spiracles subtriangular a

Taxonomy and morphology of species of the genus Squalus Linnaeus, 1758 from the Southwestern Atlantic Ocean (Chondrichthyes: Squaliformes: Squalidae)

description

Suggested common names: Atlantic lobefin dogfish; Cação-bagre-de-nadadeiras-lobadas (Portuguese). Squalus cubensis (not Howell-Rivero): Figueiredo, 1977: 8, fig. 7 (description; Southern Brazil and Uruguay).

Taxonomy and morphology of species of the genus Squalus Linnaeus, 1758 from the Southwestern Atlantic Ocean (Chondrichthyes: Squaliformes: Squalidae)

diagnosis

Diagnosis. A species of Squalus from SWAO that differs from its congeners by the combination of having markedly broad and lobe-like dorsal fins and short clasper groove, not reaching the rhipidion. Squalus lobularis sp. nov. is clearly distinct from S. mitsukurii from Japan, its morphologically closest congener, by having a slender body (vs. highly robust body in S. mitsukurii), pectoral-fin posterior margin concave (vs. pectoral-fin posterior margin straight in S. mitsukurii), narrower interorbital space (8.8 %, 6.8 % – 8.5 % TL vs. 9.3 %, 9.1 % – 9.8 % TL in S. mitsukurii); and inner clasper length 1.4 times pelvic-fin inner margin length (vs. 0.7 – 1.1 times in S. mitsukurii). Squalus lobularis sp. nov. further differs from species of the Squalus megalops group by: snout relatively long vs. snout short; pectoral fins markedly broad vs. pectoral fins often very narrow; pectoral free rear tips rounded and lobe-like vs. pectoral free rear tips often triangular; dermal denticles tricuspidate vs. lanceolate. It further differs from all its congeners by having a much larger pectoral-inner margin length (10.5 %, 9.2 % – 11.0 % TL), except from S. acanthias.

Taxonomy and morphology of species of the genus Squalus Linnaeus, 1758 from the Southwestern Atlantic Ocean (Chondrichthyes: Squaliformes: Squalidae)

discussion

Remarks. Squalus lobularis has previously been misidentified in the SWAO as S. mitsukurii a valid species originally described from Japan (Fig. 25), or as a member of the S. mitsukurii group at least in the SWAO (e. g. Figueiredo, 1981; Lucifora et al., 1999; Marques, 1999; Gomes et al., 1997, 2010). Calderón (1994) recognized S. mitsukurii off the southern Brazilian coast based on morphological characters provided by Compagno (1984), specifically proportional measurements of the head, pectoral and dorsal-fin base lengths, and pelvic-fin length. These characters occur, however, in more than one species of Squalus, which may have led to the misidentification S. mitsukurii in this region (Fig. 25). Squalus lobularis shares with S. mitsukurii a few morphological characters (Table 5): body moderately elongate; snout obtuse and markedly elongate (preorbital length 7.3 %, 7.0 % – 7.4 % TL for S. lobularis vs. 7.3 %, 7.2 % – 8.8 % TL for S. mitsukurii); nostrils closer to the mouth than to snout tip (prenarial length 1.0, 1.1 – 1.2 times inner nostril-labial length vs. 1.3, 1.1 – 1.4 times for S. mitsukurii); pectoral fins broad and smaller than head length; dermal denticles tricuspid; an

Taxonomy and morphology of species of the genus Squalus Linnaeus, 1758 from the Southwestern Atlantic Ocean (Chondrichthyes: Squaliformes: Squalidae)