Rhynchorhina mauritaniensis, Séret, Bernard & Naylor, Gavin J. P., 2016

Séret, Bernard & Naylor, Gavin J. P., 2016, Rhynchorhina mauritaniensis, a new genus and species of wedgefish from the eastern central Atlantic (Elasmobranchii: Batoidea: Rhinidae), Zootaxa 4138 (2), pp. 291-308 : 293-301

Rhynchorhina mauritaniensis sp. nov.

( Figs. 2–14 , Table 1 )

English name: False shark ray; French name: Raie-guitare mauritanienne; Hassaniya name: girhgette lemdaken G. n., sp. n.: Séret, 2009 (abstract IPFC); Séret, 2016: 1355 (in key, fig. 2).

Holotype. MNHN 2003-610, female 2040 mm TL, Iwik, Banc d’Arguin, Mauritania, caught in a trammel net, collected by IMROP fishery observers Amadou Sall, 6 February 2003. Dorsal and caudal fins, and spiral valve preserved separately. Photographs of freshly caught and defrosted specimen available.

Paratypes. (2 specimens). MNHN 2003-612, adult male 2240 mm TL (estimated, as the caudal fin had been cut, along with the dorsal fins), carcass eviscerated and dried, then rehydrated and fixed in formalin, without the dorsal and caudal fins, caught in a trammel net, Iwik, Banc d’Arguin, Mauritania, collected by IMROP fishery observer Abdallahi, 14 February 2000; photograph of freshly caught specimen available. MNHN 2003-611, male 930 mm TL, a dried skin, R’Gueïba, Banc d’Arguin, Mauritania, caught in a trammel net (tollo), collected by IMROP fishery observer Ely, 4 March 1998; photograph of freshly caught specimen available.

Diganosis. A large wedgefish (maximum TL 275 cm) with a heavy shark-like body, head somewhat flattened, snout tip broadly rounded (holotype, and paratype MNHN 2002-611) to somewhat quadrangular (paratype MNHN 2003-612). Tail with a dermal fold along each lower edge. Two large and falcate dorsal fins; caudal fin with distinct upper and lower lobes. Two conspicuous dermal folds on posterior margin of spiracles. Nostrils very large and oblique, separated from each other and from the mouth; anterior nasal flap small (not extending to inner nostril corner). Jaws moderately undulated; about 66/72 rows of oral teeth arranged in pavement. A row of pointed thorns along each rostral ridge, two/three additional thorns may occur on snout tip, single row of thornlets and thorns in front of orbit extending backward to level of spiracles; a median row of about 36 large, pointed thorns from nape to first dorsal fin and six between dorsal fins, median thorns flanked by two other shorter rows on the nape-shoulder area, additional short rows of thorns may be present on outer shoulders. Body covered with small dermal denticles, their crowns with a median posterior cusp, an extension from the median ridge, and short lateral cusp. Dorsal side greyish to greenish with numerous white ocelli-like spots; large black transverse blotch on ventral snout tip.

Description. Table 1 gives measurements expressed as proportions of total length. Very large ray with heavy shark-like body; head somewhat flattened, snout tip broadly rounded, bell-shaped, or slightly quadrangular; trunk thick, very wide at pectoral axil, then conical and tapering regularly rearward to caudal fin; tail rounded in cross section dorsally and almost flat ventrally. Apices of pectoral and pelvic fins broadly angular. Tail length from anterior cloaca 1.6 times precloacal length, 2.7 times its width at pectoral-fin insertion and 11.3 times its width at caudal-fin origin. Head rather short, its ventral length 21.0–23.2 % TL; snout short, its preoral length 10.2–10.9% TL, 1.7–1.8 times mouth width, 2.8–2.9 times internasal space; preorbital length 1.6–1.7 times interspiracular space, 1.7–1.8 interorbital space; interorbital space concave and broad; eyes moderately large, about as large as spiracles; spiracles oval with two conspicuous folds on posterior margin, the inner fold slightly smaller than the outer one.

Rhynchorhina mauritaniensis sp. nov. Rhynchobatus lübberti

MNHN MNHN MNHN MNHN 2003-0610 2003-0612 1992-0208 1992-0209 Distance snout— anterior margin of spiracle 11.7 13.0 20.9 20.7 Distance snout—posterior margin of spiracle 12.8 13.9 22.3 22.5 Orbit length 2.8 3.4 4.7 3.9

Eye ball length 1.5 1.7 3.2 2.8

Spiracle hight 2.2 1.7 2.6 2.6

......continued on the next page Rhynchorhina mauritaniensis sp. nov. Rhynchobatus lübberti MNHN MNHN MNHN MNHN 2003-0610 2003-0612 1992-0208 1992-0209 Nostril very large, elongate, oblique with inner end forming an angle of about 120°; nostril outer corner close to anterolateral margin of head; nostril length 1.2–1.3 longer than internasal space. Nostril anterior aperture slitlike, length 4.9 times in nostril length; posterior aperture long and circumflex-shaped, with shorter inner part, length 1.8 times in nostril length. Anterior nasal flap short-based, base length 3.2 times nostril length; with moderately long finger-like outer lobe and a narrow and low inner lobe; only slightly overlapping nostril, and not extending into internasal space. Posterolateral nasal flap narrow and extending about half-way along posterior margin of nostril. Mouth almost straight with thick lips and grooves around its corners; mouth width 1.2–1.3 times nostril length; jaws moderately undulated; teeth small, with blunt rhomboidal crowns, similar in both jaws, and arranged in pavement in 66/72 rows. Gill slits s-shape, distance between first gill slits 1.2–1.4 times distance between fifth gill slits.

First dorsal fin tall and rather narrow, with an narrowly rounded apex; second dorsal fin triangular, shorter than first dorsal fin, somewhat raked, and with a rather angular apex. Origin of first dorsal fin about at level of pelvic-fin inner margin; dorsal fins widely separated, interdorsal space about 2 times first-dorsal base length; interspace between second dorsal fin and origin of caudal-fin upper lobe about as long as interdorsal space. Upper lobe of caudal fin elongated with a rather angular apex; lower lobe of caudal fin well developed, ogive-shaped. Skin covered with small, close-set dermal denticles, with rounded crowns, posterior cups more or less marked off. Three distinct thornlets at snout tip; irregular row of thornlets around orbits and above spiracles; a mediodorsal row of about 36 thornlets from nape to first dorsal fin; a row of 6 thornlets between dorsal fins; a shorter row of 14–15 thornlets on each shoulder, oriented parallel to the mediodorsal row; 2–3 additional thornlets on above scapulocoracoid.

From a radiograph ( Fig. 14) the rostrum is wide, with thick rostral ridges, surrounding a wide ovoid fontanelle ( Fig. 14); the nasal capsules are oblique and elongated.

Total vertebral centra (without the synarcual segments) 200–205, with 46–48 monospondylous centra and 154–157 diplospondylous centra. Total pectoral-fin radials 64, with 38 propterygials, 10 mesopterygials, and 26 metapterygials; several radials are fused at base. Spiral valve with 15 large and several small turns.

Colour. Dorsal side greyish to greenish brown, covered with very numerous ocelli-like spots with whitish centres and rimmed by cloudy dark grey rings; spots more or less in regular rows on side of trunk; spots present on pectoral and pelvic fins; no spots or very few on head; blackish markings on shoulders in the smallest specimen, absent in large adult specimens. Thornlets around orbit and in dorsal rows with brownish tips. Ventral side white, posterior margins of pectoral and pelvic fins greyish; a large transverse black blotch (in holotype) or cluster of dark spots (in paratype) at snout tip.

Size. The largest preserved individual is the holotype MNHN 2003-612 (adult male 2240 mm TL). However, a larger male of 275 cm (total length without the caudal fin) was observed in March 1998 at Agadir, by IMROP fishery observer Kidé, but not collected.

Distribution. The new wedgefish Rhynchorhina mauritaniensis is only known from the shallow waters of shoal “Banc d’Arguin”, Mauritania, off the following localities Agadir, Iwik, and R’Guieba (Fig. 1). Biology. The female holotype had ripe ovocytes ( Fig. 12 ), and remains of unidentified shrimps in its stomach; the largest male (exceeding 275 cm TL) had five moray eels in its stomach, and weighted 44 kg (without fins). Etymology. The new species is named after the Islamic Republic of Mauritania; the country where the only known material has been collected.

Figures

FIGURE 2. Rhynchorhina mauritaniensis sp. nov., paratype MNHN 2003 - 611, male ca. 930 mm TL. A: Old photograph from IMROP showing the specimen freshly caught in 1998. B: The dried skin of the same specimen deposited in MNHN collection and stuck on a plywood board (photo B. S.).

FIGURE 3. Rhynchorhina mauritaniensis sp. nov., paratype MNHN 2003 - 612, adult male 2240 mm TL. A: Specimen freshly caught at Iwik on 14 th Febrary 2000 (photo B. Valadou). B: Same specimen rehydrated and fixed in formalin, deposited in MNHN collection (photo B. S.). C: Ventral view of freshly caught specimen (photo B. Valadou).

FIGURE 4. Rhynchorhina mauritaniensis sp. nov., holotype MNHN 2003 - 610, female 2040 mm TL. A: Specimen freshly caught at Iwik on 6 th Febrary 2003 (Photo B. Valadou). B: Dorsal view of defrosted specimen (photo B. S.).

FIGURE 5. Rhynchorhina mauritaniensis sp. nov. A: Ventral view of freshly caught MNHN 2003 - 610 (photo B. Valadou). B: Ventral view of the same specimen after rehydration (photo B. S.).

FIGURE 6. Rhynchorhina mauritaniensis sp. nov. A: Dorsal view of head of holotype MNHN 2003 - 610. B: Dorsal view of head of paratype MNHN 2003 - 612 (photos B. Valadou).

FIGURE 7. Rhynchorhina mauritaniensis sp. nov., holotype MNHN 2003 - 610. A: Dorsal and caudal fins that were cut off by a fisherman. B: Fins in place maintained with clips (photos B. S.).

FIGURE 8. Rhynchorhina mauritaniensis sp. nov., holotype MNHN 2003 - 610. A: Head, ventral view. B: Right nostril. C: Mouth (photos B. S.).

FIGURE 9. Rhynchorhina mauritaniensis sp. nov., paratype MNHN 2003 - 612. A: Head, ventral view (photo B. Valadou). B: Right nostril. C: Mouth (photos B. S.).

FIGURE 10. Rhynchorhina mauritaniensis sp. nov., holotype MNHN 2003 - 610, dorsal view of snout showing three small thorns at tip (photo B. S.).

FIGURE 11. Rhynchorhina mauritaniensis sp. nov., holotype MNHN 2003 - 610, spiral valve (photo B. S.).

FIGURE 12. Rhynchorhina mauritaniensis sp. nov., holotype MNHN 2003 - 610, ovary with ripe ovocytes (photo B. S.).

FIGURE 13. Rhynchorhina mauritaniensis sp. nov. (drawing by J. F. Dejouannet).

Tables

TABLE 1. Morphometric measurements expressed as percentage of total length (TL) of the holotype of Rhynchorhina mauritaniensis sp. nov., MNHN 2003 - 610, female 2040 mm TL, paratype MNHN 2003 - 612, male adult 2240 mm TL, and of two specimens of Rhynchobatus lübberti from West Africa, MNHN 1992 - 208, male 790 mm TL, and MNHN 1992 - 209, male 805 mm TL.

	Holotype female	Paratype male adult	Congo-Gabon male	Sénégal male
Measurement in % TL Fork length	2040 mm TL 85.4	2240 mm TL	790 mm TL 94.2	805 mm TL 94.8
Disc width Head length (dorsal) Snout width at level of spiracle Distance snout—D1	36.8 12.5 18.1 40.5	37.3 13.7 18.6 42.9	39.7 22.7 20.2 52.3	39.5 21.7 19.5 50.1
Distance snout—D2 Distance snout—caudal fin	57.9 71.1	60.3 73.5	70.0 86.0	68.2 84.3
D1 anterior margin length D1 hight D1 base length D1 inner margin length	10.8 11.2 5.7 4.9		13.2 9.3 5.7 4.8	13.8 11.8 5.0 5.2
D1 posterior margin length Distance D1 - D2	10.7 11.5		9.8 12.2	9.9 12.5
D2 anterior marginlength D2 hight D2 base length D2 inner margin length	10.8 9.8 4.9 3.7		12.0 9.5 4.9 4.2	12.0 9.9 5.1 4.4
D2 posterior margin length Caudal upper margin length	8.8 11.5		8.4 15.0	9.3 15.2
Caudal hight Caudal lower lobe anterior margin length Distance snout—pectoral apex Distance snout—anterior margin of orbit	13.4 8.9 28.5 8.7	30.4 9.5	12.5 10.1 39.1 17.0	13.8 10.8 40.0 16.9
Distance snout—anterior margin of eye ball	9.3	10.1	17.7	17.5