Myoglanis aspredinoides, Carlos Donascimiento & John G. Lundberg, 2005

Carlos Donascimiento & John G. Lundberg, 2005, Myoglanis aspredinoides (Siluriformes: Heptapteridae), a new catfish from the Río Ventuari, Venezuela., Zootaxa 1009, pp. 37-49 : 39-44

Myoglanis aspredinoides new species

Figs. 1-3, Table 1

Holotype. MBUCV-V- 25388 , 95.6 mm SL. Venezuela, Estado Amazonas, Rio Ventuari, Laguna Pavon , in pool behind beach of Rio Ventuari, on south side of river, ca. 12 km from its confluence with Rio Orinoco ; 4° 4´N, 66° 56´W; 24 January 1991; B. Chernoff, A. & D. Machado-Allison, J. Wheeler .

Paratypes. ANSP- 162492 , 63 mm SL. Same locality as holotype; 25 March 1987; B. Chernoff, W. G. Saul, J. Fernández, M. E. Antonio and M. E. Gutierrez. FMNH- 104481 , 149.9 mm SL. Collected with the holotype .

Diagnosis. A species of Myoglanis with 32-35 anal-fin rays (vs. 25-28 in M. koepckei and 16-21 in M. potaroensis ); caudal fin lanceolate (vs. caudal fin bifurcated in M. koepckei and forked, divided to the base of the rays in M. potaroensis ); anterior margin of pectoral spine with low, retrorse serrations only distally and without erect dentations along middle and proximal end of spine (vs. erect dentations present along entire anterior margin of pectoral spine in M. koepckei and M. potaroensis ) and 56-57 vertebrae (vs. 47 in M. koepckei and 46 in M. potaroensis ).

Description. Morphometric data given in Table 1. Body greatly elongated (Fig. 1), depressed before dorsal fin, ellipsoidal at level of dorsal-fin origin and subquadrangular immediately in front of pelvic fin-origin, gradually more compressed caudally. Dorsal profile from snout margin to IO1 pore convex, slightly concave in preorbital and interorbital regions, flat in postorbital region, slightly convex from occipital region to dorsal-fin origin, concave along dorsal-fin base and straight to caudal-fin base. Ventral profile of head slightly convex, nearly straight from posterior margin of branchiostegal membranes to end of anal-fin base, and sloping downward along caudal peduncle. Lateral profile of head parabolic in dorsal view with a weak constriction behind rictus delimiting snout.

Head ~1.5 times longer than wide, dorsally covered by thick skin. Adductor mandibulae muscles prominent on cheeks and extending dorsally over skull roof posterior to eyes. Snout long and wide with dorsolateral groove accommodating maxillary barbel immediately posterior to its insertion and extending posteriorly to about midpoint of eye. Mouth terminal with fleshy, coarsely plicate lips and broad rictal folds. Mouth corners extending posteriorly along sides of head. Lips with conspicuous sulci dividing each lip in two folds. Upper jaw projecting slightly beyond lower jaw. Premaxilla with a longitudinally wide subrhomboidal patch of villiform and minute teeth arranged in up to six irregular series, its posterolateral corners strongly projected posteriorly. Lower jaw with similar dentition disposed in up to six irregular rows and continued posterolaterally. Maxillary barbel ellipsoidal in cross-section and short, extending to distal margin of pectoral fin. Outer mental barbel inserted slightly behind inner mental barbel, and short, its distal tip reaching groove at posterior margin of second lateral-most branchiostegal ray. Inner mental barbel inserted anterior to apex of gular fold and its distal tip reaching half again its length beyond apex. Branchiostegal membranes free, joined to isthmus only at gular apex and not overlapping medially, with six branchiostegal rays. Anterior nares tubular and immediately above margin of upper lip. Posterior nares closer to eye than anterior nares, longitudinally elongated, and surrounded by an elevated fleshy rim, highest along its anterior border and notched posteriorly. Eye ovoid and small, completely dorsal and protruding, closer to snout tip than opercle margin, subcutaneous without a free orbital margin, but with a superficial lateral fold, skin covering eye thin and translucent.

Cephalic sensory canals simple (Fig. 2). Supraorbital canal with four pores. SO1 broad, medially adjacent to anterior naris. SO2 posteromedial to anterior naris, approximately at mid-distance of internarial length. SO3 at posteromedial corner of posterior naris. SO4 (epiphyseal) pores paired, close together near midline, located at level of posterior ocular border. SO5 and SO6 (parietal) pores absent. Infraorbital canal with six pores. IO1-3 wide like SO1. IO1 at posterolateral corner of anterior naris. IO2 above maxillary groove, just behind maxillary barbel base. IO3 above maxillary groove, at level of anterior ocular border. IO4 slightly posterolateral to eye. IO5 behind eye. IO6 posterior and dorsal on head. Preoperculomandibular canal with 11 pores, those from preopercle with wide foramina. Mandibular symphyseal pores paired. Anteriormost three pores of the mandibular branch wide like SO1 and IO1. Postotic canal with two pores above opercle and gill opening. Lateral line canal complete, reaching hypurals. First two pores of main canal close together, second pore right above first pore, both pores on short membranous branches, remaining pores located just above canal.

Dorsal fin margin convex and containing eight lepidotrichia, the first a reduced spinelet, completely covered by skin and not visible externally, associated with supraneural. Second lepidotrich or first dorsal-fin ray (homologous with dorsal-fin spine) unbranched, its basal third ossified and distally segmented; six remaining dorsal-fin rays branched, third and fourth longest. Distal tips of adpressed posterior rays reaching adipose-fin origin. Base of dorsal fin, including basal parts of rays, covered by thick skin. Seven basal radials supporting dorsal fin, first basal radial associated with neural spine of vertebra 6 and last basal radial above vertebra 14. Neural spines of vertebrae 9 to 15, below dorsal fin oriented almost horizontally. Adipose fin elongate and low, originating at about 40% of SL and above anal-fin origin. Adipose fin united to dorsal margin of caudal fin, its posterior lobe obsolete except for a slight notch. Basal half of adipose fin covered by a conspicuous thick layer of adipose tissue. Anal fin elongate with 32 to 35* rays, first two or three rays simple. Anal fin supported by 32 to 33* basal radials, first basal radial inserted posterior to haemal spine of vertebra 18* or 19 and last basal radial inserted anterior to haemal spine of vertebra 45* or 46. Caudal fin lanceolate with i,15,i* or i,16,i principal rays, seven branched rays articulating with upper hypural plate and eight branched rays associated with lower hypural plate, 8* to 10 dorsal procurrent rays and 9* to 13 ventral procurrent rays. Caudal skeleton with three separate hypural plates: parhypural; hypurals 1+2; hypurals 3+4+5 (both paratypes with a separate hypural 5).

Pectoral fin with a strong sharp spine (Fig. 3) and 8 to 9* branched rays ( FMNH paratype with eight rays on the left side and seven rays on the right side). Spine with three to five retrorse regular serrae along distal portion of anterior margin and three to five erect dentations along proximal portion of posterior margin. Pelvic fin with i,5 rays, anterior margin of first ray and anterior branch of second ray pinnate, lepidotrich segments with long antrorse extensions, fourth ray longest, pelvic-fin origin in a vertical through base of fourth branched dorsal-fin ray.

Total vertebrae 56* to 57, 15* or 16 precaudal and 41caudal, lateral processes of first nine* or ten free vertebrae supporting ribs.

Anus located approximately equidistant from medial edge of pelvic-fin base and analfin origin. Urogenital papilla elongated and separate from anus, located slightly in advance of mid distance between center of anus and anal-fin origin.

Color in alcohol. A lightly pigmented species with an overall light tan ground color on body and head plus fine, darker brown chromatophores scattered on dorsum, sides and on head onto lips and rictal fold. Lowermost sides and venter immaculate. No lateral stripes, spots, or differential pigmentation of tympanic area over swimbladder. Eyes black. Dorsal and adipose fins hyaline except for finely peppered thick skin along fin bases. Caudal-fin rays lightly peppered most densely along the longest middle rays. Anal and paired fins hyaline.

Distribution and habitat. Myoglanis aspredinoides is recorded only from the Río Ventuari, a tributary of the upper Orinoco river basin in Venezuela, in stagnant pools formed by rocks and around 2 m of maximum depth, with clear waters and sandy and muddy bottom.

Etymology. The specific epithet makes allusion to the remarkable resemblance in external appearance of this species to species of the catfish genus Aspredo of the family Aspredinidae.