Squatina dumeril Le Sueur, 1818

Vaz, Diego F. B. & De, Marcelo R., 2013, Morphological and taxonomic revision of species of Squatina from the Southwestern Atlantic Ocean (Chondrichthyes: Squatiniformes: Squatinidae), Zootaxa 3695 (1), pp. 1-81 : 50-53

Squatina dumeril Le Sueur, 1818

Lectotype. MNHN A-9692, adult male (1172 mm TL), off coast of New York state, United States, 40o S 67o W (for locality details, see Bertin, 1939) (lectotype herein designated).

Additional non-type material examined. MNHN A-9691, adult male (1090 mm TL), New York, New York state, United States, 40o 40’1”S 73o49’59”W; USNM 118461, juvenile female (382 mm TL), continental slope off New York, United States, 39o 42’ N, 71o 17’ W; USNM 400796, juvenile male (320 mm TL), off Panama, 9o15’54” N, 81o40’54” W.

Comments on type-material. The syntype of S. dumeril (MNHN A-9692) and another non-type specimen (MNHN A-9691) collected near the syntype and at about the same time were examined in the MNHN. These are dry, stuffed specimens; many characters of external morphology, therefore, as well as morphometric proportions and coloration, are poorly preserved. However, features of the dermal denticles and teeth could be studied, confirming that S. dumeril is similar to Southwestern Atlantic Squatina species in external morphology and in some proportions ( Figs. 37 , 38 ). One difference, however, concerned pectoral fin length (28.7% TL in lectotype, 23.9% TL in non-type specimen, in S. dumeril ), values not found in S. argentina and only occasionally encountered in specimens of S. occulta and S. guggenheim (even though it is almost 4% below the mean for these species). However, poor preservation must be taken into account; the specimen of S. guggenheim with lower pectoral fin length (MNRJ 14, 27.1% TL) was also a taxidermal specimen.

Measurements given by Bigelow and Schroeder (1948) for S. dumeril present some differences from the lectotype. They reported a pectoral fin anterior margin length about 2% TL greater than the lectotype, 2.7% TL shorter interspiracular distance, 3.2% TL shorter mouth width, 3.6% TL shorter upper caudal lobe, and 4% TL greater distance between pelvic origin to origin of upper caudal lobe. However, as commented above for Squatina sp., due to observed variation in Southwestern Atlantic Squatina and preservational distortions these differences were not considered significant (see Tabs. 1 , 3 , 5 ).

Bigelow and Schroeder (1948) described the morphology of the anterior nasal flap as presenting two elongate barbels, positioned on inner (elongate) and outer (triangular-shaped) extremities of nasal flap, without a medial lobe, which is different from all Southwestern Atlantic Squatina species. The examination of Bigelow and Schroeder’s specimen (USNM 118461) showed that the median lobe is present, but less developed than for other species reported in the present study, similar to the illustration in the original description of Le Sueur (1818). The lectotype has this feature partially preserved (left nostril only). The nasal barbel in the lectotype presents an elongate and spatulate inner lobe and an enlarged outer lobe that is somewhat triangular, more than three times wider than inner lobe, with its distal tip missing; no conspicuous medial lobe was observed in the lectotype, as described by Bigelow and Schroeder (1948). However, this may be preservational. Futher studies are necessary to understand the relevance of this character as a diagnostic feature. Dermal folds are present in the lectotype along its entire lateral head margin, without projections of any kind, similar to that described above for other Southwestern Atlantic Squatina species.

Tooth morphology and rows in the lectotype are arranged as in S. guggenheim and S. occulta , in 20 rows on both upper and lower jaws (tooth formula 11-9/10-10), slightly different from the accounts of Bigelow and Schroeder (1948) and Castro (2011), in which the tooth formula is given as 10-10/9-9. However, as reported for Southwestern Atlantic species above, this may be due to intraspecific variation (see Tabs. 2 , 4 , 6 ). Upper teeth slightly smaller than lower teeth; on both arches, teeth on inner two vertical rows and on two distalmost vertical rows proportionally smaller than central teeth. Inner, upper rows closer to symphysis than the equivalent rows on lower jaw. Lingual surface (only surface available for study) with a bulky, upright and lingually bent main cusp, without serrations or cusplets. Crown base projecting laterally and with prominent lateral heels ( Fig. 38 c).

Another relevant feature of S. dumeril described by Bigelow and Schroeder (1948, fig. 104c) is the presence of a single row of enlarged and morphologically distinct dorsal midline denticles in juvenile specimens (morphologically similar to S. guggenheim ). These authors also reported adults of S. dumeril with dorsal midline denticles slightly larger than surrounding denticles. Although the lectotype and non-type specimen examined present dorsal midline denticles only slightly larger than surrounding denticles, confirming Bigelow and Schroeder's (1948) observation, these midiline denticles are slightly different between the MNHN specimens, similar to the differences reported in other species of Southwestern Atlantic Squatina . However, based on our small sample and that there is variation in dermal denticles at least in S. guggenheim , the diagnostic value of dorsal midline denticles in S. dumeril cannot yet be determined. The lectotype has dorsal midline denticles similar to other dorsal denticles, but with a slightly enlarged basal plate (about 1.5 times diamenter of other dorsal denticles) and crown with four ridges ( Fig. 39 ; similar to S. occulta ). Non-type specimen with midline denticles morphologically distinct from other dorsal denticles, with enlarged basal plate (1.5 to 2 times diameter of other dorsal denticles), conical crown, crown base with ridges (variable number depending of preservation), and crown-apex without any ridge (similar to midline denticles in adults of S. guggenheim ).

Enlarged denticles on dorsal head surface conical, with large basal plate and tall crown, morphologically distinct from other dorsal denticles, and without observable ridges over surface of crown (probably due to preservation). Morphology and distribution of cephalic enlarged denticles very similar to adults of other Southwestern Atlantic Squatina species (two clusters with five or more denticles dorsally on snout region positioned more or less in a row leading toward eyes, one cluster of denticles anterior and another posterior to eyes, and a pair of clusters of denticles between spiracles (also Bigelow and Schroeder, 1948). The cluster of denticles between spiracles distinguishes S. dumeril from S. argentina and Squatina sp., in which denticles between spiracles are absent or reduced, respectively ( Fig. 38 a). Similar to adult males of S. guggenheim , the lectotype of S. dumeril and non-type specimen examined have enlarged denticles over outer edge of dorsal pectoral fin surface, sparcely grouped, without smaller denticles in between.

Claspers present in both specimens of S. dumeril , proportionally and morphologically similar to S. guggenheim , but with slight differences. Clasper groove extending from close to pelvic fin insertion posteriorly to hypopyle. Anterior half of the cover rhipidion and free margin of rhipidion cover the outer half of the clasper glans. Cover rhiphidion of lectotype of S. dumeril positioned anteriorly and medially close to aperture of hypopyle, and not projecting posterolaterally to rhipidion, as in S. guggenheim ; however, this feature may be affected by preservation. Bigelow and Schroeder (1948, p. 538, fig. 105b) described a distinctive lateral caudal keel posterior to second dorsal fin (‘caudal peduncle expanded laterally as a low ridge’). This feature could not be clearly observed; however, the lectotype has an observable lateral expansion on the caudal peduncle posterior to second dorsal fin ( Fig. 38 e).

Figures

FIGURE 37. Lectotype of Squatina dumeril (MNHN A- 9692, off coast of New York state, United States, 1172 mm TL).

FIGURE 38. Morphological details of Squatina dumeril (MNHN A- 9692). A) Dorsal view of head. B) Dorsal view of pectoral fin. C) Labial view of lower jaw showing the tooth rows. D) Apex of pectoral fin outer edge with enlarged dermal denticles showing sexual dimorphism. E) Lateral view of dorsal fins. F) Dorsal view of clasper. Abbreviations: crh, cover rhiphidion; dd, enlarged dermal denticles; rh, rhiphidion. Scale bar = 50 mm.

FIGURE 39. Anterior region of tail in lectotype of S. dumeril (MNHN A- 9692) in dorsal view (A), and dermal denticles of dorsal midline on caudal region, anterior to first dorsal fin (B). Arrows indicate dermal denticles with basal plate slightly larger than surrounding denticles. Anterior to left.