Psammobatis rutrum

Psammobatis rutrum View in CoL Jordan, 1891

Psammobatis rutrum Jordan, 1891:334 (original description; type-locality: near Gulf San Matías, Argentina). —McEachran, 1983:58, fig. 16c (systematic study). — McEachran, Dunn, 1998:286 (systematic study). —Compagno, 1999:489 (listed). —Cousseau et al., 2000:31 ( Argentina and Uruguay; catalogue). — Menni, Stehmann, 2000:87 ( Argentina, Uruguay and Brazil; listed). —Paragó, 2001 (systematic study). —Gomes, 2002 (systematic study). —Gomes, Gadig, 2003:29 ( São Paulo, Brazil; listed). —Mabragaña, 2007 ( Argentina; biological and ecological study). —Cousseau et al., 2007:70 (Mar del Plata; Argentina; catalogue). —Weigmann, 2016:100 (listed). —Last et al., 2016:461 (listed). —Nión et al., 2016:23 ( Uruguay; listed). —Martins, Oddone, 2017 ( Brazil; reproductive biology). —Viana et al., 2017:3 ( Rio de Janeiro, Brazil; diet). —Cordeiro, Oddone, 2019:47 ( Rio Grande do Sul, Brazil; reproductive biology). —Gomes et al., 2019:301, fig. 293 ( Rio de Janeiro, Brazil; catalogue). —Brum-Neto, Lucena, 2020 ( Brazil; tooth morphology). Sabadin et al., 2020:1900–1 ( Argentina, Uruguay and Brazil; listed). — Batista et al., 2021 (Barra de Santos, São Paulo, Brazil; reproductive biology). —Mabragaña, Cousseau, 2021:65 ( Argentina; listed).

Raia extenta —Garman, 1913:356 (systematic account).

Malacorhina cirrifer —Regan, 1914:16 (systematic account).

Psammobatis extenta —Figueiredo, 1977:33, fig. 74 (Southern Brazil; catalogue).

Diagnosis. Psammobatis rutrum is distinguished from P. extenta and P. lentiginosa by the brown coloration pattern with whitish spots distributed randomly throughout dorsal region ( vs. tiny dark dots in P. extenta and dark dots in P. lentiginosa ); dark dot on the central of pectoral fins in adults and juveniles ( vs. absent in adults in P. extenta and P. lentiginosa ); tiny spots concentrated in preorbital region ( vs. distributed around orbits P. extenta and absent in P. lentiginosa ); pectoral thorns with tip oriented towards lateral margin of disc ( vs. tip oriented towards caudal region in P. extenta and reduced or absent in P. lentiginosa ); interruption of the three rows of dorsal thorns posterior to scapular region ( vs. continuous rows of dorsal thorns in P. extenta and interruption only from the middorsal to pelvic insertion in P. lentiginosa ); anterior fontanelle trapezoidal ( vs. rectangular in P. extenta ); basal fenestrae kidney-shaped ( vs. rectangular and narrow in P. extenta ); posterior nasal cartilage oblique in relation the anteroposterior axis ( vs. perpendicular in relation the anteroposterior axis in P. extenta ); dorsal terminal cartilage 2 triangular ( vs. plate-shaped in P. lentiginosa and absent P. extenta ); accessory terminal cartilage 2 flattened dorsoventrally ( vs. projected transversely to lateral in P. lentiginosa and absent in P. extenta ); accessory terminal cartilage 1 articulated with the ventral marginal cartilage ( vs. continuous in P. extenta ).

External description. Disc 1.5–1.7 times wider than long ( Tab. 4). Heart-shaped disc in juvenile and adult specimens; subtle in the former and accentuated in the latter. Adults with wide pectoral fins and convex margins in the posterior region, while the anterior region narrows towards the snout. Adult males with concave anterior disc margin close to the orbital region; disc width at eye line in females is 1.2 times longer than in males.

Preorbital length 2.5–3.2 times eye horizontal diameter and 2.5–2.6 times interorbital distance. Preoral length 1.3–1.7 times mouth width. Upper jaw arched, especially in middle region; lower jaw convex. First pair of gill openings 1.3 times larger than fifth. Distance between the first gill slits 1.8–1.9 times the distance between fifth.

Pelvic fins convex externally with a notch forming anterior and posterior lobes. Pelvic anterior lobe shorter with a convex anterior margin; posterior margin distinguished by radial tips and continuously connected to the lateral margin of posterior lobe. Posterior lobe with a convex lateral margin and a straight inner margin. Dorsal fins similar in size and shape, with rounded apex. Distance from pelvic posterior margin to the origin of first dorsal fin 1.9–2.1 times distance from first dorsal origin to posterior margin of caudal fin. Tail long, 1.8–1.9 times in total length and 1.2–1.3 times the snout-vent distance. Caudal fin rounded.

Coloration in alcohol. Dorsal coloration brown ( Fig. 3E). Adults with whitish spots all over the dorsal surface. Dark spot in the central region of each pectoral fin and another in each region of malar thorns in both adults and juveniles ( Figs. 3E, 5C). A cluster of dark spots located on posterior region of each pectoral fin (may not be visible in juveniles). Preorbital region with tiny dark spots, projecting towards disc margin ( Fig. 4C). Some specimens present a black spot on snout tip as in P. extenta and P. lentiginosa . Tail region presenting the same predominant background color. Ventral region uniformly cream ( Fig. 3F).

Dermal denticles. Rostral and malar thorns forming rows with no differences between sexes; star-shaped base and a curved crown that narrows towards its distal end ( Figs. 11C–D). Adult males with rows of alar thorns situated posterior to the malars and positioned horizontally, close to the pectoral lateral margin, with the distal end oriented medially; elongated base and a thorn-shaped crown, arranged in one to three alternating rows, with around five to 20 denticles ( Fig. 11A; Tab. 2).

Head with one to five preorbital thorns, one to three midorbital thorns, none to two postorbital thorns, and one to four spiracular thorns. Thorns similar in structure to the nuchal and scapular but smaller. Nuchal and scapular thorns forming a triangular grouping, organized into one to three nuchal thorns and five to 17 scapular thorns. Scapular thorns more dispersed, resulting in an arch in some individuals; leaf-shaped base with shallow grooves and a curved crown with an extremely sharp distal end ( Figs. 11E–F).

No mid-pectoral thorns on pectoral fins. Pectoral thorns scattered randomly throughout the pectoral fin and varying in size; stellate base poorly defined and tip slightly inclined to posterior margin of pectoral fin ( Figs. 7C–D). Posterior pectoral thorns present in both males and females. Larger and more clustered; cross-shaped or star-shaped base, with a curved crown and tapered distal end. Males lack dermal denticles on their claspers ( Fig. 9C).

Middorsal and dorsolateral thorns with an interruption after between scapula and pelvic insertion ( Fig. 11F). Middorsal and dorsolateral thorns similar in structure to nuchal and scapular thorns. Smaller denticles present posteriorly to scapula and around rows. Cross-shaped base and crown curved with a tapered distal end.

One row of mid-caudal thorns and two caudo-lateral thorns, one on each side of tail, all oriented anteroposteriorly; denticles arranged randomly between rows. Caudo-lateral thorns with base and crown flattened dorsolaterally. Mid-caudal thorns similar in structure to middorsal thorns and forming a continuous row with them, with around 15 to 34 denticles ( Tab. 2).

Geographical distribution. Although some specimens do not have the capture locality, the distribution is also between the coasts of Rio de Janeiro, São Paulo, and, mainly, Rio Grande do Sul ( Fig. 9). Records of P. rutrum are also found in northern Argentina (Cousseau et al., 2007).

Material examined. USNM 43431 About USNM , holotype , near Gulf San Matías , off the coast of Argentina, Albatross Station 2678, 42°00’24”S 61°38’30”W, depth 78 meters. São Paulo GoogleMaps : DBAV. UERJ 848.3 *, female, 230 mm TL, 140 mm DW, Santos. Rio de Janeiro : DBAV. UERJ 2142.8 *, female, 251 mm TL, 144 mm DW, Angra dos Reis . MNRJ 607 View Materials , 3 View Materials , 242–264 mm TL, 110.15–160 mm DW, Ilha Rasa . MNRJ 32626 View Materials , female, 263 mm TL, 151 mm DW, Rio de Janeiro . MNRJ 33565 View Materials , 3 View Materials , 247–265 mm TL, 133–166 mm DW, between Ilha Rasa and Marambaia. Rio Grande do Sul : MNRJ 20610 View Materials , 2 View Materials , 203–245 mm TL, 130–142 mm DW. MZUSP 9953 View Materials , male, 235 mm TL, 134 mm DW. MZUSP 9954 View Materials , female, 242 mm TL, 140 mm DW. MZUSP 13128 View Materials , female, 231 mm TL, 142 mm DW. MZUSP 13129 View Materials , female, 242 mm TL, 143 mm DW, 31°19’0.0”S 50°22’0.0”W GoogleMaps . MZUSP 45151 View Materials , 2 View Materials , 125.4 View Materials – 257 mm TL, 75.3–147 mm DW, 31°48’0.0”S 50°22’0.0”W GoogleMaps . MZUSP 45152 View Materials *, male, 240 mm TL, 140 mm DW, 31°50’0.0”S 50°21’0.0”W. Locality undetermined GoogleMaps : DBAV. UERJ 2130 *, male, 251 mm TL, 137 mm DW. AC. DBAV. UERJ 937.1 , male, 215 mm TL, 125 mm DW. MNRJ 20609 View Materials , 2 View Materials , 194–222 mm TL, 115.35–117.4 mm DW.

Statistical analysis. Significant differences between males and females were observed in six measurements within P. extenta , five in P. lentiginosa and seven in P. rutrum ( Tab. S1). In P. extenta , measurements with significant p-values (<0.05) were prenasal length ( T: 2.577, df = 35, p = 0.014), eye diameter ( T: -3.156, df = 28, p = 0.004), preoral length ( T: 2.4161, df = 31, p = 0.021), mouth width ( T: -2.1475, df = 35, p = 0.039), distance between fifth gill slits (W: 191, p = 0.001) and disc width at eye line ( T: 4.4696, df = 35, p = 0.000). For P. lentiginosa , the significantly different measures were preorbital length ( T: 2.8283, df = 20, p = 0.010), prenasal length (W: 93, p = 0.010), preoral length ( T: 5.7438, df = 20, p = 0.000), distance between fifth gill slits ( T: 3.7949, df = 20, p = 0.001) and disc width at eye line ( T: 4.3859, df = 20, p = 0.000). In P. rutrum , significant differences were observed in prenasal length ( T: 3.6525, df = 20, p = 0.002), eye diameter ( T: -2.4898, df = 21, p = 0.021), preoral length (W: 116, p = 0.000), mouth width (W: 29, p = 0.033), distance between first gill slits ( T: 3.4305, df = 18, p = 0.003), distance between fifth gill slits ( T: 5.4503, df = 14, p = 0.000) and disc width at eye line ( T: 6.9238, df = 21, p = 0.000).

Analyses between species resulted in seventeen measurements with p-values lower than 0.05, in the Kruskal-Wallis test ( Tab. S2). Using Dunn’s test, differences between species were identified for each variable analyzed ( Tab. S3). Differences between P. extenta and P. lentiginosa were observed for caudal length (p = 0.000), disc length (p = 0.012), preorbital length (p = 0.000), prenasal length (p = 0.000), internasal distance (p = 0.000), eye diameter (p = 0.000), preoral length (p = 0.000), snout-vent length (p = 0.000), mouth width (p = 0.000), distance from first dorsal fin origin to posterior end of caudal fin (p = 0.001). For P. rutrum and P. extenta , significant variables were disc width (p = 0.005), disc length (p = 0.001), internasal distance (p = 0.046), eye diameter (p = 0.028), snout-vent length (p = 0.000) and distance between fifth gill slits (p = 0.044). For P. lentiginosa and P. rutrum , significant values were obtained for the variables disc width (p = 0.048), caudal length (p = 0.000), preorbital length (p = 0.001), prenasal length (p = 0.008), internasal distance (p = 0.023), interorbital distance (p = 0.042), preoral length (p = 0.005), mouth width (p = 0.007), distance from first dorsal fin origin to posterior end of caudal fin (p = 0.000), distance from posterior margin of pelvic fin to first dorsal fin origin (p = 0.000), first gill slit width (p = 0.019) and fifth gill slit width (p = 0.004).

Comparative morphology of internal structures.

Neurocranium. The neurocranium of the three Psammobatis species is compressed dorsoventrally and has an hourglass shape, with the greatest width located in the medial section of the nasal capsules and the second greatest in the section of the otic capsules ( Figs. 12–14). Rostrum not observed, but it is very thin and uncalcified, not continuous or fused to the neurocranium (McEachran, 1983).

Nasal capsule slightly oblique in relation to the anteroposterior axis, with thin walls and a basal fenestra, located in the anterodorsal region, varying from kidney-shaped in P. rutrum and P. lentiginosa to rectangular and narrow in P. extenta ( Figs. 12–16). Nasal aperture relatively narrow, 1.4–1.5 times in the internasal distance ( Tab. 5). Antorbital facet lies on the lateral surface of the nasal capsule, close to its posterior margin, and articulating to the antorbital cartilage. Nasal cartilages not preserved in P. lentiginosa . In P. extenta and P. rutrum , outer nasal cartilage triangular and short, not dividing incurrent and excurrent apertures ( Fig. 16). Internal nasal cartilage rectangular in shape and running laterally from the nasal fontanelle, adjacent to the internasal septum, dorsal and attached to the posterior nasal cartilage medially. Posterior nasal cartilage narrow at the anterior tip, wide and rounded at the posterior tip and perpendicular in relation the anteroposterior axis in P. extenta , while uniformly wide and oblique in relation the anteroposterior axis in P. rutrum ( Fig. 16).

Cranial roof extends from the posterior margin of the anterior fontanelle to the parietal fossa. Anterior fontanelle rectangular in P. extenta and trapezoidal in P. rutrum and P. lentiginosa ( Figs. 12–15), limited anteriorly by the anterior cranial margin, extending to the anterior edge of the supraorbital ridge. Epiphyseal bridge thin, equivalent to 4.9–7.1 times the length of the anterior fontanelle ( Tab. 5). Posterior fontanelle sub-rectangular, 1.6–1.7 times longer than the anterior fontanelle ( Tab. 5). Posterior margin moderately pointed in P. lentiginosa while slightly pointed in P. extenta and P. rutrum ( Fig. 15). Preorbital process continuous with the supraorbital ridge and relatively developed in P. extenta and P. rutrum , while it is less noticeable in P. lentiginosa ( Fig. 15).

Orbital region delineated anteriorly by the posterior wall of the nasal capsules and posteriorly by the anterior margin of the otic capsules, dorsally delimited by the cranial roof and ventrally by the basal plate ( Fig. 17). Orbital wall perforated by several foramina for the passage of cranial nerves and blood vessels. Oronasal canal lies anteriorly and near the posterior wall of nasal capsules. Foramina for the anterior cerebral vein situated posterior to the oronasal canal. Foramina for the ophthalmicus nerve situated dorsally near the supraorbital crest. Posterior to the foramen for the optic nerve (II) and dorsal to the optic nerve foramen, there is a single foramen for the trochlear nerve (IV). The foramen for the optic nerve lies anteriorly to the half-length of orbital wall, quite near the foramina for the anterior cerebral vein in P. rutrum than in P. extenta and P. lentiginosa ( Fig. 17). Posterior to the foramen for the trochlear nerve is the foramen for the oculomotor nerve (III), posterior to half-length of orbital wall. The foramen for the afferent pseudobranchial artery is located ventrally to the foramen for the oculomotor nerve, close to the basal plate. Dorsally, on the same vertical line as the foramen for the afferent pseudobranchial artery, is the foramen for the abducens nerve (VI) in P. lentiginosa and P. extenta , while in P. rutrum it is located posteriorly on the same horizontal line. Anterior to the otic region, the foramina for superficial ophthalmic is located in dorsal portion, the foramen prootic in medial portion and the foramen for the passage of the hyomandibular ramus of the facialis nerve (hVII), in ventral portion ( Fig. 17).

Basal plate begins anteriorly at the ethmoidal fossa right after the nasal capsules, runs to the posteroventral end of the optic region and ends at the ventral margin of the foramen magnum. A single foramen for the internal carotid artery ventrally situated and slightly anterior to the level of the postorbital process ( Fig. 16).

Otic region begins posterior to orbital wall and extends to occipital region, containing otic capsules, impressions of semicircular canals and parietal fossa. Parietal fossa lies posteriorly and between otic capsules, with a pair of endolymphatic canals (smaller apertures) and another pair of perilymphatic canals ( Fig. 16). Hyomandibular facet elongated and positioned obliquely on the lateral otic region, lined dorsally by the postorbital groove and jugal arch ( Fig. 17).

Occipital condyle situated on the lateral margin of the foramen magnum and lateral to it lies the foramen for the vagus nerve (X). Lateral to the foramen for the vagus nerve lies the foramen for the glossopharyngeal nerve (IX).

Clasper. The clasper of the three Psammobatis species is slender and covered entirely by the dorsal and ventral lobes of glans. External morphology varies mainly in terms of the coverage of dermal denticles and the position of the spermatic groove. Dermal denticles present along the margins of spermatic groove in P. extenta and absent in P. rutrum and P. lentiginosa . Spermatic groove and hypopyle located entirely in lateral position in P. rutrum and P. lentiginosa , while found in dorsal position in P. extenta ( Figs. 8, 18).

Clasper skeleton consists of a slender axial cartilage and considerably tapered distal end in P. lentiginosa and P. rutrum , while slightly tapered distally in P. extenta ( Figs. 19–20). Dorsal marginal cartilage distally tapered, reaching the level of the articulation between ventral marginal and ventral terminal cartilages in P. extenta , while in P. lentiginosa and P. rutrum it is truncated with distal margin articulated with proximal margin of dorsal terminal 2 cartilage, which is absent in P. extenta ( Figs. 19–20). Dorsal terminal 2 cartilage dorsoventrally flattened, plate-shaped with a narrow proximal margin and large medial region in P. lentiginosa , while triangular in P. rutrum , with a large proximal margin and tapered distal end. Ventral marginal cartilage elongated and uniform, in P. lentiginosa , and distally robust, in P. rutrum , articulating with the proximal margins of accessory terminal 1 cartilage and accessory terminal 2 cartilage; in P. extenta , it is uniformly narrow up to the level of the articulation with ventral terminal, where it expands slightly as it extends distally continuously to the accessory terminal 1 cartilage. Ventral terminal cartilage elongated and spoon-like, in P. extenta and P. lentiginosa , and short with blade-shaped distal end in P. rutrum ; proximal margin articulated with ventral marginal cartilage, in P. extenta , while proximal margin articulated with accessory terminal 1, in P. lentiginosa and P. rutrum . Accessory terminal 2 cartilage projected transversely to lateral and tapered distally in P. lentiginosa , flattened dorsoventrally and tapered distally in P. rutrum and absent in P. extenta . Accessory terminal 1 cartilage tapering anteroposteriorly, projected transversely to lateral at its medial portion, and with a rounded posterior tip, in P. extenta ; proximally robust and distally acute, in P. lentiginosa ; dorsoventrally flattened and with a tapered distal tip, in P. rutrum ( Figs. 19–20).