Xyliphius anachoretes, Figueiredo & Britto, 2010

Figueiredo, Carlos A. & Britto, Marcelo R., 2010, A new species of Xyliphius, a rarely sampled banjo catfish (Siluriformes: Aspredinidae) from the rio Tocantins-Araguaia system, Neotropical Ichthyology 8 (1), pp. 105-112 : 106-110

Xyliphius anachoretes , new species

Fig. 1

Holotype. MNRJ 31923 , 88.4 mm SL, Brazil, Goiás, rio Tocantins below the dam of Serra da Mesa Hydropower Plant, in a marginal pond at the mouth of rio Preto , an affluent of the right bank of rio Tocantins (currently under water of the Cana Brava Hydropowerplant reservoir), 13°37’51”S 48°07’01”W, collected in daylight, 3 Dec 1996, D. F. Moraes (Equipe Ímpar).

Paratype. MZUSP 89546 , 25.6 mm SL, Brazil, Goiás, municípios de Crixás /Santa Terezinha de Goiás, rio Crixás-açu , under bridge at the state road GO-465, 14°26’26”S 49°42’37”W, 28 Jul 2005, Equipe CBE .

Diagnosis. Xyliphius anachoretes is diagnosed from its congeners, except X. magdalenae , by the presence of six developed retrorse serrae along posterior border of pectoral spine (vs. 7-9 in X. melanopterus and X. barbatus , 8 in X. lombarderoi , 8-10 in X. lepturus and X. kryptos ). Xyliphius anachoretes differs from X. magdalenae by the lower number of total free vertebrae (31 vs. 33-36).

Xyliphius anachoretes is further distinguished, except from X. kryptos , by papillae of lower lip bearing minute branches (vs. large branches in X. lepturus , X. barbatus , X. lombarderoi , and X. melanopterus , or unbranched papillae in X. magdalenae ) ( Fig. 2 ); and, except from X. magdalenae and X. kryptos , by the presence of 22 or 24 papillae on lower lip (vs. 25-28 in X. lepturus , 27-29 in X. melanopterus , 27-30 in X. barbatus , and 28 in X. lombarderoi ).

Besides, Xyliphius anachoretes is also promptly distinguished by the lower number of dorsal procurrent rays (two) from X. lepturus (four or five), X. melanopterus (three), and X. magdalenae (four).

Description. Morphometric data presented in Table 1 . Head depressed, roughly triangular with bluntly rounded snout in dorsal view. Skull ornamentation inconspicuous. Dorsal profile straight from tip of snout to origin of caudal fin, except for shallow convexity from posterior tip of parietosupraoccipital to posterior base of dorsal fin. Ventral profile convex from tip of snout to pectoral girdle region, then straight to pelvic-fin origin, shallowly concave from pelvics to analfin origin, ascending obliquely along anal-base and finishing straight along caudal peduncle. Body depressed anteriorly, becoming gradually compressed towards caudal fin. Entire body banjo-shaped in dorsal/ventral view, greatest width at cross-section through region just anterior to pectoral-spine insertions.

Eye very small, diameter 1.5% (holotype) or 2.4% (paratype) of head length, without free orbital margin; located dorsally in anterior half of head. Two nares, anterior one tubular with four separate papillae along its lateral (lower) margin, located at anterior edge of snout; outermost papillae smaller than internal ones. Posterior nare as small opening located at midpoint between anterior nare and eye. One maxillary barbel on side of snout, inserted just above rictus. Maxillary barbel reaching pectoral-fin base. Two mental barbels, both smaller than maxillary. Inner mental barbel smallest, its length shorter than half-length of outer mental barbel. Inner mental barbel located just posterior to mouth opening, and at distance of one-quarter of mouth width from midventral axis of head. Outer mental barbel half the length of maxillary barbel, reaching or slightly surpassing transverse through mouth opening when adducted anteriorly. Outer mental barbel located on transverse posterior to inner mental barbel, separated from it by distance greater than inner mental barbel length. Mouth subterminal, wider than snout with 22 (paratype) or 24 (holotype) fleshy, finger-like papillae along border of lower lip. Almost all papillae the same size and weakly dendritic with one to three minute branches ( Fig. 2b ). Anterior margin of snout with shallow medial notch ( Fig. 2b ). Gill opening small, restricted to valvular slit, covered by fleshy skin flap on ventral surface of head. Gill membranes united to isthmus. Small genital papillae just posterior to anus.

Head, trunk and fins all covered by thick skin somewhat loosened from muscular tissues, particularly at bases of paired fins and on abdomen. Skin of head and trunk covered by unculiferous tubercles. Head tubercles larger than those on body. Most of head tubercles roughly hexagonal and depressed; tubercles on snout and maxillary barbel rounded, decreasing in size from proximal to distal tip of barbel. Five lateral rows of large tubercles extending from post-cephalic region to base of caudal fin. Prominent crest along dorsal midline from supraoccipital region to dorsal-fin origin, and from base of last dorsal-fin ray to caudal fin. Tubercles on all fin rays small and rounded; tubercles depressed and striated on interradial membranes. Skin tubercles larger and more tightly spaced on dorsal surface of body and head than on ventral surfaces. Tubercles on ventral surface minute and somewhat scattered, except those around mouth and just posterior to last anal-fin ray, which are more similar to dorsalsurface tubercles.

Sixteen latero-sensorial pores on head. Anterior branch of the supraorbital branch with five pores: one pore mesially, and two posterior to the anterior naris; fourth pore located mesially to a line between anterior and posterior nares; and fifth pore located just in front of posterior naris. Two mesial pores, corresponding to epiphyseal and parietal branches, respectively. Four pores of the infraorbital branch of laterosensory system; anteriormost dorsally close to rictus. Five pores of the preoperculomandibular branch; anteriormost pore ventrally close to rictus. Lateral line with 17/18 pores on left and right sides, respectively. Lateral line not extending onto caudal fin.

Total number of vertebrae 31, precaudal vertebrae 11, caudal vertebrae 20. Six pairs of ribs, first pair articulated with parapophyses of first free (sixth) centrum, and slightly larger than others. Ribs gradually decreasing in size caudally.

Dorsal fin I,3,i; roughly triangular, located slightly anterior to mid-standard length. Dorsal spinelet absent. Dorsal spine (second dorsal lepidotrichia) feeble. Anal fin ii,4,i; roughly semi-ovoid, its origin just posterior to tip of longest ray of abducted pelvic fin. Pectoral fin I,4,i; origin just posterior to cheek; profile roughly ellipsoid, tip reaching (paratype) or falling short of (holotype) midlength of pelvics when abducted. Pectoral spine thick with six developed retrorse serrae along its posterior margin, decreasing in size from distal tip to proximal base of spine. A rudiment of serrae (detectable only on x-ray imaging; Fig. 3 , arrow) sprouts proximally. Ossified portion of pectoral spine shorter than first pectoralfin ray. Pectoral slit just above base of last pectoral-fin ray. Pelvic fin i,4,i; roughly triangular; origin just posterior to vertical through dorsal-fin origin. Caudal-fin roughly rectangular, its distal margin truncate. Principal caudal-fin rays

i,4/4,i; dorsal and ventral procurrent caudal-fin rays 2 and 4, respectively.

Color in alcohol. Ground color of body and head brown, ventral region slightly lighter than dorsal. Irregular light brown middorsal stripe on head from tip of snout to transverse through pectoral-fin origins; stripe widest in interorbital region. All barbels yellowish light brown. Two elongate, irregular, light brown blotches along dorsal midline of body: anterior one small, just in front of dorsal-fin base, posterior one large, extending from base of last dorsal-fin ray to vertical through midlength of anal-fin base.All fin rays and membranes dark brown; borders yellowish white.

Distribution. Xyliphius anachoretes is currently known only from two localities, one in the upper rio Tocantins (type locality) and the second from the upper rio Araguaia ( Fig. 4 ).

Ecological notes. Both specimens were captured by day in shallow waters. Due to its diminished eyes and rough skin somewhat free from underlying muscles, together with its extreme rarity in collections, we speculate that Xyliphius anachoretes is a cryptic fossorial species.

Etymology. The specific epithet of Xyliphius anachoretes is from the Greek anachoretes , meaning “one that retired from the world”, hermit, recluse, in allusion to the rarity of the only two specimens known, each one found alone and far apart. An adjective.

Figures

Fig. 1. Xyliphius anachoretes new species, holotype, MNRJ 31923, 88,4 mm SL: Brazil, Goiás State, rio Tocantins below the dam of Serra da Mesa Hydropower Plant, in a marginal pond at the mouth of rio Preto, a right margin tributary of the rio Tocantins (currently under water in the Cana Brava Hydropower-plant reservoir).(a) dorsal view; (b) ventral view; (c) lateralview.

Fig. 2. Ventral view of head and papillae on lower lip of: (a) Xyliphius magdalenae, BMNH 1947.7.1.215.216, 70.0 mm SL; (b) X. anachoretes, MNRJ 31923, holotype, 88.4 mm SL; (c) X. melanopterus, FMNH 99492, 101.5 mm SL; and (d) X. lepturus, FMNH99489, 108.1 mm SL. Scalebar = 1 mm.

Fig. 3. Radiograph of anterior region of Xyliphius anachoretes, MNRJ 31923, holotype, 88.4 mm SL, showing premaxilla lateral to mesethmoid, and completely separated from its pair.Arrows showing rudimentary serrae on pectoral spines.

Fig. 4. Known distribution of Xypliphius species. Records of Xyliphius anachoretes represented by stars at the rio Tocantins-Araguaia system (highlighted). Type locality represented by a solid star. Other species represented are X. melanopterus (open squares); X. lepturus (solid squares); X. kryptos (open triangle); X. magdalenae (solid triangle; type locality); X. lombarderoi (open circle, type locality); X. barbatus (solid circle, type locality). Squares and solid triangle may represent more than one record.