Rhamdia eurycephala, Angrizani & Malabarba, 2018

Angrizani, Rafael C. & Malabarba, Luiz R., 2018, Morphology and molecular data reveal the presence of two new species under Rhamdia quelen (Quoy & Gaimard, 1824) (Siluriformes: Heptapteridae) species complex, Zootaxa 4388 (1), pp. 41-60 : 53-55

Rhamdia eurycephala sp. nov.

urn:lsid:zoobank.org:act: D4454851-6512-4D80-BA2B-3EBACAE73D9F ( Fig. 9 ; Table 4)

Holotype. UFRGS 19908 , 246.6 mm SL, Brazil, state of Santa Catarina, municipality of Anitápolis, rio do Povoamento, hydrographic basin of rio Tubarão , 27°51’36”S, 49°07’50”W; R. C. Angrizani, L. R. Malabarba, M. C. Malabarba, 21 Feb 2015.

Paratypes (Total = 58). All from Brazil, Santa Catarina State: MCP 17617, 23 (2 c&s), municipality of Anitápolis , creek tributary to rio Pinheiro, rio Tubarão, 27°53'59"S, 49°06'59"W ; W. Koch, 15 Jan 1995. UFRGS 19908 , 16 (1 c&s), collected with holotype, municipality of Anitápolis, rio do Povoamento, hydrographic basin of rio Tubarão , 27°51’36”S 49°07’50”W, R . C. Angrizani, L.R. Malabarba, M.C. Malabarba, 21 Feb 2015. MZUSP 121730, 3 , municipality of Anitápolis, rio do Povoamento, hydrographic basin of rio Tubarão , 27o51’50”S 49°07´54”W, R . C. Angrizani, L.R. Malabarba, M.C. Malabarba, 21 Feb 2015. UFRGS 19906 , 16 , municipality of Anitápolis, rio do Povoamento, hydrographic basin of rio Tubarão , 27o51’50”S 49°07´54”W, R .C. Angrizani, L.R. Malabarba, M.C. Malabarba, 21 Feb 2015.

Diagnose. Rhamdia eurycephala differs from all congeneric species by having the head width at eye level greater than the body width at pectoral-girdle.

Description. Measurements in Table 1. Body elongated; cross section of trunk roughly circular at dorsal-fin origin and along dorsal-fin base, gradually compressed posteriorly to caudal peduncle. Anterodorsal profile of body convex from supraoccipital to dorsal-fin base. Dorsal-fin base nearly straight, posteroventrally slanted, and scarcely convex from dorsal-fin to base of caudal fin. Ventral body profile nearly straight from mouth to caudal-fin base. Body widest at pectoral-girdle and deepest at dorsal-fin origin. Caudal peduncle longer than deep. Number of post-Weberian vertebrae 39(1) or 40(2).

Head depressed and flat dorsally; wider than pectoral girdle at eye level. Dorsal head profile straight and rising from snout tip to supraoccipital in lateral view. Snout broadly rounded in dorsal view, longer than deep. Head shape polygonal in dorsal view; cheek convex, especially in large specimens due to enlargement of adductor mandibulae muscle. Dorsal limit of adductor mandibulae muscle marked by deep longitudinal facial ridge extending from base of maxillary barbel to level of anterior border of eye. Transverse distance between posterior nares slightly smaller than that between anterior nares. Mouth wide, subterminal, larger than interorbital distance; snout projecting slightly beyond lower jaw. Gape transverse, with large, fleshy rictal fold at corners. Both upper and lower lips with several longitudinal plicae.

Barbels flattened, wide at their base and tapering towards distal tip. Maxillary barbel longest; length variable, maximally exceeding first rays of dorsal fin; inserted above upper lip and posterolateral to anterior nare. Two pairs of mental barbels with bases aligned. Outer mental barbels barely reaching origin of pectoral fin in smaller specimens, never reaching pectoral fin in larger specimens. Inner mental barbels shorter than outer mental barbels. Tip of adpressed inner mental barbel extending beyond posterior margin of branchiostegal membrane. Gular fold distinct and V -shaped. Branchiostegal rays 5(3). Gill rakers thick and moderately long, with 9(2), 8(1) rakers on first ceratobranchial, and 2(3), on first epibranchial. Eye large, slightly elliptical (longitudinally elongated); rim circumscribed by deep, continuous invagination that is distinctly more pronounced along lateral border. Eye positioned dorsally, approximately at midpoint between tip of snout and corner of opercular membrane; interorbital space widel. Pupil rounded. Sensory channels of the head simple.

Dorsal fin with two unbranched rays and six branched rays, distal margin convex and base length less than or equal to fin height. First unbranched dorsal-fin ray small and not externally visible, second unbranched ray stiffened proximally, segmented distally. Dorsal-fin origin anterior to midlength between pectoral and pelvic-fin origins; insertion of last branched ray just before or at pectoral-fin origin. Tip of last branched dorsal-fin ray not reaching anterior insertion of adipose fin. Adipose fin long; with ascendant curve in lateral profile and conspicuous posterior free lobe. Adipose-fin origin at vertical through middle of depressed pelvic fin and posterior insertion at final third of caudal peduncle.

Pectoral fin small with one unbranched and five branched rays; when adpressed, reaching approximately origin of third branched dorsal-fin ray. Unbranched ray of pectoral-fin stiffened, straight and with strong serrations along distal anterior side and basal posterior side. Pelvic fin rounded, small (9.8–12.5% SL) and approximately same size as pectoral fin, having one unbranched ray and five branched rays, distal tip surpassing genital papilla, never reaching anal-fin origin. Pelvic-fin origin nearly at middle of standard length, after insertion of last dorsal-fin ray. Anal fin rounded, with three unbranched rays and seven, eight or nine branched rays; when adpressed, never exceeds posterior insertion of adipose fin. Length of anal-fin base equal to that of dorsal fin. Caudal fin deeply forked, lobes rounded; dorsal lobe slightly smaller in depth and length; seven branched rays in dorsal lobe and nine branched rays in ventral lobe.

Colour of preserved specimens. Body grayish with or without irregular small brown spots. Head and fins grey without spots. Ventral portion of body and head white. Dorsal fin with dark band across middle length of rays. Maxillary barbels same colour as body.

Distribution. Known from upstream portion of two tributaries to the Tubarão River Basin, in the state of Santa Catarina, Brazil.

Etymology. The name comes from the Greek eury meaning broad, wide, and kephale meaning head. A noun in apposition.

Figures

FIGURE 9. Rhamdia eurycephala (UFRGS 19908), holoTyPe, 246.6 mm SL. In dorsAl, lATerAl,And venTrAl views.