Malacoraja obscura, de Carvalho & Gomes & Gadig, 2005

de Carvalho, Marcelo R., Gomes, Ulisses L. & Gadig, Otto B. F., 2005, Description of a new species of skate of the genus Malacoraja Stehmann, 1970: the first species from the southwestern Atlantic Ocean, with notes on generic monophyly and composition (Chondrichthyes: Rajidae), Neotropical Ichthyology 3 (2), pp. 239-258 : 241-246

Malacoraja obscura , new species

Holotype. MNRJ 28289 , adult female, 680 mm TL, 19 o 39’57"S, 038 o 38’26"W, state of Espírito Santo ( Brazil), 808 m, sta. D-0503, N/O Thalassa , 29 Jun 1999 ( Fig. 1) . Paratypes. (4 specimens). MNRJ 28290 , juvenile male, 505 mm TL, 19 o 39’57"S, 038 o 38’26"W, state of Espírito Santo ( Brazil), 808 m, sta. D-0503, N/O Thalassa , 29 Jun 1999 ( Fig. 2) ; MNRJ 28291 , juvenile male, 355 mm TL, 19 o 39’57"S, 038 o 38’26"W state of Espírito Santo ( Brazil), 808 m, sta. D-0503, N/O Thalassa , 29 Jun 1999 ( Fig. 3a) ; MNRJ 28292 , juvenile male, 295 mm TL, 19 o 39’57"S, 038 o 38’26"W, state of Espírito Santo ( Brazil), 808 m, sta. D-0503, N/O Thalassa , 29 Jun 1999 ( Fig. 3b; dissected for sensory canals, neurocranium, scapulocoracoid and ventral gill arch muscles) ; MNRJ 28293 , juvenile female, 251 mm TL, 21 o 46’34"S, 039 o 53’22"W, state of Rio de Janeiro ( Brazil), 1105 m, sta. E-547, N/O Thalassa , 6 Jul 2000 .

Diagnosis. A species of Malacoraja distinguished from all congeners by presenting small, scattered, and faded whitish spots on dorsal disc and pelvic fins, an irregular row of small thorns along dorsal midline of tail which persists in larger specimens (extending from tail base to two-thirds of tail length), and ventral tail midline devoid of small denticles only at base (naked region not extending beyond pelvic fins). The following characters in combination further distinguish M. obscura , n. sp.: ventral disc and tail with a uniform dark brown coloration, absence of scapular thorns in larger specimens, relatively higher number of tooth rows (64/62 tooth rows in subadult male of 505 mm TL, and 76/ 74 in large female of 680 mm TL), relatively higher number of vertebrae (27-28 Vtr, 68- 75 Vpd), paired postventral fenestrae on scapulocoracoid, enlarged posterior postventral fenestra, circular foramen magnum, and paired internal carotid foramina on neurocranial basal plate. The significance of these features among species of Malacoraja is discussed below.

Description. Proportional morphometrics are presented in Table 1, and counts in Table 2 (where they and compared to other species of Malacoraja ). The description below is based on all specimens, but salient features of the holotype are separately mentioned.

External morphology. Disc cordiform, much wider than long (DW 60.3-67.5 % of TL, DL 47.5-53.1 % of TL), with greatest width just posterior to its horizontal midline. Snout extremity not greatly elongated but clearly projecting beyond anterior disc margin. Anterior margin of disc relatively straight from disc apices to snout tip, not convex from level of orbits to snout tip. Disc apices broadly rounded, with widely convex and broad posterior margins. Posterior lobe of disc extending caudally to about one-half of length of posterior lobe of pelvic fin. Smaller specimens with more acute snout angle (100- 101 o, vs. 105-107 o in larger specimens; Figs. 1-3), appearing more triangular in outline. Disc relatively thin and dorsoventrally compressed. First three gill openings slitlike, horizontal wider than both posterior openings (especially fifth); posterior openings semicircular. Gill openings situated just medial to propterygia; fifth gill openings just anterior to coracoid, situated at anterior coracoid corners; distance between fifth openings slightly greater than half of distance between first openings.

Eyes and spiracles closely set; spiracles positioned near outside margins of eyes (interspiracular distance greater than interorbital distance); spiracles projecting obliquely from midline ( Fig. 4). Orbital length greater than spiracle length. Spiracle oval, elongated, extending anteriorly to posterior onefourth of eye. Nine pseudobranchial folds on anterior spiracular wall in most specimens (holotype with 10); folds knoblike and short. Prenasal distance much shorter than preorbital distance. Preorbital distance just less than one-third of disc length. Nasal curtain covering large nasal apertures extensive, but with only a small, semicircular nostril; nasal flaps small and tube-like, more prominent on lateral (incurrent) nostril margin; nasal flaps around nostril not distally fringed ( Fig. 5). In smaller specimens, posterior margin of nasal curtain slightly concave medially, but strongly concave in holotype, exposing upper jaw teeth. Lateral borders of nasal curtain sigmoidal. Posterior lobes of nasal curtain weakly fringed. Nasal curtain length at midline about one-half of greatest width (at posterior corners). Distance between nostrils about equal to distance between mouth corners. Mouth situated at about midorbital level. Mouth opening more or less straight across (more so in females), but upper jaw with slight median indentation which accomodates median projection of lower jaw.

Teeth set in quincunx, with circular to trapezoidal, flattened crowns and weakly pointed cusps; cusps not longer than tooth base length or width (no adult males examined). Crowns with well developed aprons anteriorly, but with weak uvula posteriorly, when present. Roots very large, almost as wide as cusps; tooth base bilobed, with lobes separated by a shallow basal median groove (in some teeth the lobes appear contiguous); basal root ornamentation weakly apparent (tooth morphology indistinct from M. senta ; see Herman et al., 1994: plate 22). Teeth covering jaw integument for almost full width of mouth opening; teeth anteroposteriorly arranged in a very slender tooth band (widest at symphysis), arranged in just a few series (in some 10 horizontal rows at symphysis in largest male and in holotype). Tooth rows as follows: 76/74 rows in 680 mm TL holotype (symphysis at row 38/37; some portions of tooth bands missing in holotype, but not affecting counts), 64/62 rows in 505 mm TL male (symphysis 33/31), 57/ 55 in 355 mm TL male, 54/ 51 in 295 mm TL male, and 48/ 44 in 251 mm TL female ( Table 2).

Pelvic fins much wider than long, with two very distinct lobes ( Fig. 6). No sexual dimorphism in pelvic fin shape (mature males unknown). Greatest pelvic fin width (with expanded anterior lobes) slightly smaller than one-half of disc width.Anterior lobe limblike, slender and greatly elongated; posterior lobe with convex posterior margins and about as wide as nasal curtain width. Origin of anterior lobe slightly anterior and ventral to pectoral fin insertion; anterior lobe with first articulation just posterior to its midlength and second articulation at about onefifth of its length. Posterior lobes extend caudally beyond anterior lobes, inserting on both sides of ventral tail base posterior to cloaca; axils separated by a small space. Outer pelvic fin margins weblike, with greater inflection separating anterior and posterior lobes in holotype and larger juveniles; smallest female with less indented outer pelvic margin.

Claspers in largest male extending posteriorly to pelvic fin posterior margin (adult males unknown; Fig. 6). Claspers dorsoventrally compressed, expanding slightly at clasper glans region, at about clasper midlength (more evident in largest male). Claspers about one-half of length of inner margin of posterior lobe of pelvic fins in males 355 and 295 mm TL, and equal to inner margin of posterior lobe in male 505 mm TL. Clasper groove more or less straight in largest male, curving slightly with expansion of glans distally. Clasper with a very small, distal fleshy projection, pointing slightly outward (as in adults of other species of Malacoraja ). Internal clasper components not developed even in largest male, but shield, with slightly folded epithelium, extends from more or less level of hypopyle to distal section of glans. Elongate terminal ridge, possibly representing the incipient dike, about onethird length of glans. Inside of glans pigmented on both internal and external surfaces. Denticles and pseudosiphon absent from clasper.

Tail slender and elongate, clearly demarked from disc, and tapering from pelvic base to extremity. Cloaca to tail length greater than snout to cloaca length, but tail length not as great as disc width. Tail wider than high in cross-section throughout its entire length. Lateral tail folds moderately developed, not flaplike, extending from slightly posterior to tail midlength to distal tip (in holotype and larger male, tailfolds originate at more or less tail midlength). Tail folds resemble ridges anteriorly, and widest close to dorsal fins. Tail more dorsoventrally compressed at extremity compared to origin. Dorsal fins situated on posterior-most aspect of tail, not fleshy and without robust bases. Dorsal fins confluent at bases, low and long, similarly shaped, and broadly sloping posteriorly. Dorsal fin base length variable, more or less equal in length in some specimens. First dorsal fin without conspicuous free posterior lobe. Second dorsal fin slightly greater than first in some specimens, with enlarged posterior free lobe inflecting anteriorly to insert on low caudal fold. Caudal fold very low, with a straight dorsal contour, and higher dorsally than ventrally. Lateral tail folds meet ventrally just posterior to second dorsal fin base to form ventral caudal fold. Distal segment of caudal fold dorsoventrally continuous, wrapping around caudal extremity. Length of caudal fold just greater than length of second dorsal fin base.

Squamation. Almost entire dorsal surface of disc covered by numerous, closely set, more or less uniformly distributed and evenly spaced, minute dermal denticles (denticles slightly more spaced out in larger specimens) ( Figs. 4, 6, 7). Minute denticles present on integument over eyes, but absent from inside spiracles (even from integument on anterointernal ledge formed by spiracular cartilages). Denticles on middisc region (close to shoulder girdle) slightly larger and more spaced apart (especially over suprascapulae); minute denticles also present anterior to nasal capsules, but anterior-most tip of projecting snout without denticles in some specimens. Pectoral axils mostly without small denticles. Pelvic fins with anterior lobes completely devoid of denticles; denticles on pelvic fins present only on caudal portion of posterior lobe, but not as numerous as over disc (i. e., only dorsally exposed portions of pelvics with small denticles). Dorsal and lateral tail with numerous denticles ( Fig. 7); denticles on lateral tail slightly larger. Dorsal fins covered with small denticles, except membrane between both fins and dorsal posterior bases. Lateral tail fold and caudal fin generally devoid of denticles as well (a few present in holotype).

Few thorns present antero- and posteromedially to eyes, in midline over dorsal disc and tail, and on shoulder girdle in smaller specimens. Most thorns morphologically distinct from smaller denticles, with oval, more pedunculate bases, and thicker crowns and bases ( Fig. 7a, b, d, e). Enlarged thorns proximal to eyes and scapular region more evident in smaller specimens; some thorns possibly missing from specimens due to abrasion, especially on disc midline (see Table 2 for thorn counts). In holotype, nuchal thorns on disc midline originate at middistance between spiracles and shoulder girdle. Nuchal thorns few and evenly spaced apart (six in holotype, some missing), extending posteriorly to anterior suprascapular margin. Three midscapular thorns present in holotype. Middisc thorns present just posterior to shoulder girdle, but absent at more or less middisc, reappearing cau- dally anterior to pelvic girdle. In larger male, caudal midrow of thorns originates posterior to pelvic girdle. Midrow of tail thorns originates with row of isolated larger thorns, interspersed with smaller thorns, and continues caudally with irregular row of larger and smaller thorns ( Fig. 7a, b). Larger, more numerous thorns in midrow posterior to pelvic axils, frequently with two or three adjacent thorns ( Fig. 7d, e). Midrow thorns reduce in size and merge with smaller denticles as of approximately posterior two-thirds of tail. Smaller specimens with less conspicuous midrow over tail and posterior disc region. Larger male lacking alar and malar thorns, but with larger denticles anterolaterally on disc.

Ventral disc region and pelvic fins mostly smooth. A small patch of distinct denticles on anterior segment of ventral rostrum and in a few rows on anterior disc margins lateral to rostral appendix (more pronounced in holotype, extending posterolaterally to about one-half of rostrum length). Ventral snout denticles more spaced apart and larger than minute denticles on dorsal side. Smallest male without ventral snout denticles, but other males with same pattern as holotype. Ventral snout denticles with star-shaped and slender bases, usually with four basal projections (anterior, posterior and two lateral; the former two usually much longer than the lateral segments); denticle crowns acute and curved, pointing rearward ( Fig. 7c).

Minute denticles present on ventral aspect of tail, extending from pelvic fin posteriorly to level of first dorsal fin origin; ventral caudal distal extremity mostly naked. Denticles missing from ventral midtail base region; denticles on ventral tail mid base present as of one-half of length of posterior lobe of pelvic fin in most specimens (in holotype and larger male paratype, central band without denticles on ventral tail extends posteriorly to about posterior margin of pelvics; Fig. 6c). Denticles on lateral aspect of tail larger and more closely grouped together than those on ventral tail region. Denticles on ventral snout region ( Fig. 7c) and tail morphologically similar, but former with longer bases and taller crowns.