Hemigrammus taphorni, Ricardo C. Benine & Guilherme A. M. Lopes, 2007

Ricardo C. Benine & Guilherme A. M. Lopes, 2007, A new species of Hemigrammus Gill, 1858 (Characiformes: Characidae) from Rio Caura, Venezuela., Zootaxa 1610, pp. 53-59 : 54-58

Hemigrammus taphorni , sp. nov.

(Figs. 1-2, Table 1)

Holotype. MCNG 55841 , 31.1 mm SL, Rio Caura, Cano Mayor, around Salto Para , 6 31’67” N, 64° 48’33” W. State of Bolivar, Venezuela. 28 September 1982. S.Reid and D. C. Taphorn.

Paratypes. MCNG 55842 , 8, 23.8 -34.2 mm SL, collected with the holotype. MCNG 55843 , 22, 23.8 - 42.2 mm SL, 2 C&S, 40.2-41.3 mm SL, affluent of Rio Caura NE (CVG-Tecmin Grp 1-heliport) (450 m NE from heliport) , 6 38’0” N, 64° 37’24”W. State of Bolivar, Venezuela. 04 April 1989, L. Nico, L. Delgado, B. Stergios and Y. Estrega. MZUSP 94720 , 3, 30.5-32.9 mm SL, same data of MCNG 55843.

Diagnosis. The combination of the following features distinguishes the new species, H. taphorni , from all congeners: presence of an elongate dorsal fin (more evident in adult males) with an anterior dark area; concentration of dark pigments on the distal portion of the second through fourth branched anal-fin rays (resulting in a dark dash in this area); presence of a single humeral spot and caudal spot reaching the tip of the middle caudal-fin rays; premaxillary teeth of the outer row bearing only three cusps; three scale rows below the lateral-line. A detailed comparison to congeners that are more similar is provided in the Remarks below.

Description. Morphometric data for Hemigrammus taphorni is summarized in Table 1. Body fusiform. Greatest body depth at dorsal-fin origin. Dorsal profile of head straight or slightly concave. Dorsal profile of body convex, from posterior tip of supraoccipital spine to dorsal-fin origin, slightly convex and posteroventrally slanted along dorsal-fin base, slightly convex from posterior terminus of dorsal-fin base to end of adipose-fin origin, and concave along caudal peduncle. Ventral body profile convex from tip of lower jaw to caudal-peduncle origin, slightly concave along caudal peduncle. Prepelvic region transversally flattened, more so proximal to pelvic-fin insertion. Postpelvic region transversally flattened proximal to pelvic-fin insertion, becoming somewhat obtuse toward anal-fin origin.

Mouth terminal. Maxilla trespassing vertical through anterior margin of orbit. Premaxillary teeth in to rows; outer tooth row with 3 (6), 4* (30) tricuspid teeth, midcentral cusps longer than others; inner tooth row with 4(1) 5*(35) tetra- to pentacuspid teeth, midcentral cusps longer than others. Maxillary with 1(3), 2*(23), 3(8), 4(2) tri- to pentacuspid teeth. Dentary with 4 pentacuspid teeth followed by a smaller tricuspid one, and a series of small teeth, with 1-3 cusps (fig. 2).

Nostrils closer to anterior orbital margins than to each other. Suparaoccipital process short, its tip not reaching the vertical through posterior margin of opercle.

Dorsal-fin rays ii, 9. Pectoral-fin rays i,10* (23), i,11 (11), i,12(1). Tip of pectoral fin slightly trespasses vertical through pelvic-fin insertion. Adipose fin well developed. Pelvic-fin rays i,7, when adpressed, its tip reaches second branched anal-fin ray. Anal-fin rays iv, 21 (2), 22* (20), 23 (11), 24 (2). Principal caudal-fin rays i,17, i. Caudal-fin forked.

Scales cycloid, with few radii along posterior border. Lateral-line incomplete, pored scales 9(2), 10(4), 11*(9), 12(5), 13(1) 14(2). Lateral series scales including lateral-line scales 30(2), 32*(8). Scale rows between dorsal-fin origin and lateral-line 5; scale rows between lateral-line and pelvic-fin origin 3. Circumpeduncular scale rows 11*(4), 12(4). Scale sheath along anal-fin base in a single series of 6-7 scales, extending posteriorly to seventh branched anal-fin ray.

First gill arch with 10(2), 11*(21), 12(12) gill rakers on ventral limb and 5(5), 6* (24), 7(6) on dorsal limb. Precaudal vertebrae 15, caudal vertebrae 19. Supraneurals 4.

Sexual dimorphism. Adult males with very small hooks on the first five to seven branched anal-fin rays. The hooks are located on the last basal segments and on the segments of the posterior branch of each hooked ray. All hooks are backward pointed and varying in number from two to four per ray segment. Adult males also present a more elongate dorsal fin as a secondary sexually dimorphic feature (fig 3).

Color in alcohol. Overall coloration yellowish tan. Mid-dorsal line darker. Humeral region with a dark spot located on second to third lateral line scales, extending 2-3 horizontal series of scales, including lateralline. Dark chromatophores scattered on infraorbitals and opercle. A dark thin stripe extending along septum horizontal, more evident on posterior half of body. A three-scale deep band of sparsely scattered dark chromatophores extending along midlateral body. Limits of posterior hypoaxial myomeres enhanced by dark pigments. Caudal peduncle with a faint horizontal oval-shaped spot. Dorsal fin with scattered dark pigments, more concentrated on anterior half. Anal fin with scattered dark pigments, more concentrated along its proximal and distal extension, resulting in a clearer medial area. Tip of anterior anal-fin rays densely pigmented by dark chromatophores resulting in a dark dash in this area. Paired fins hyaline with scattered dark pigments, more concentrated on unbranched rays. Caudal fin with a narrow field of dark chromatophores on its distal margin.

Distribution. Known only from the type locality, the Río Caura, a tributary of Río Orinoco, Venezuela (fig. 4).

Etymology. This species is named after Donald C. Taphorn, collector of our new species and whose work has greatly contributed to our knowledge of Neotropical ichthyology.

Remarks. Géry (1977) proposed five artificial Hemigrammus groups based basically on the color pattern of its species. These were: (a) H. gracilis-group - species without black markings; (b) H. bellotti-group - species with one (or two) humeral spot(s) and no caudal spot; (c) H. tridens-group - species with caudal spot and no humeral spot (for example the Costello tetra); (d) H. ocellifer-group - species with both a humeral (eventually two) and a caudal spot; (e) H. unilineatus-group - species with a black spot on dorsal fin.

Géry (1977) listed 13 species in the H. ocellifer-group , including those with one humeral spot ( H. megaceps , H. caudovittatus , H. barrigonae , H. guyanensis , H. iota , H. boulengeri , H. vorderwinkleri , H. schmardae , and H. melanochrous ) and with two humeral spots ( H. pretoensis , H. luelingi , H. ocellifer , and H. pulcher ). Hemigrammus taphorni differs from H. megaceps , H. caudovittatus , and H. barrigonae by presenting a longitudinal faint stripe extending from the humeral spot to caudal spot, which is not observed in the latter. H. taphorni is distinguished from H. guyanensis by lacking the iridescent spots flanking the caudal peduncle posteriorly (vs. present in the latter). H. taphorni is promptly distinguished from H. iota and H. vorderwinkleri by presenting 21-24 branched anal-fin rays (vs. 15-17 and 18 anal-fin rays, respectively). H. taphorni is easily distinguished from H. schmardae by possessing up to three maxillary teeth with five cusps (vs. one or two maxillary teeth conical or with three cusps in the latter). The rare species from rio Madeira, H. melanochrous , presents only 17 branched anal-fin rays (vs. 21-14 in H. taphorni ) and has a greatest body depth of 24.0% (vs. 32.7-42.2% in H. taphorni ).

More recently, Bertaco & Carvalho (2005) described H. skoliplatus from rio Tapajôs, and treated their new species as belonging to the H. ocellifer-group . The higher number of branched anal-fin rays (21-24) also distinguishes H. taphorni from H. skolioplatus , which bears 14-16 branched anal-fin rays. Zarske et al. (2006) described H. ora , also included in H. ocellifer-group , which is easily distinguished from H. taphorni by presenting an edentulous maxilla. Finally, H. taphorni is clearly distinguished from species of the H. ocellifer-group with two humeral spots by presenting a single humeral spot.

Within the H. unilineatus-group , H. taphorni is most similar in its color pattern to H. elegans , a species originally described from rio Tapajôs basin. Taphorn (1992) tentatively identified 50 specimens from Río Orinoco drainages as H. aff. elegans . The examination of images of the syntypes of Tetragonopterus elegans (= H. elegans ), and its original (Steindachner, 1882) and subsequent descriptions (Eigenmann, 1918; Géry, 1977) demonstrated that H. taphorni is promptly distinguished from H. elegans by the presence of three horizontal scale rows below the lateral-line (vs. four or five in H. elegans ), and by the presence of premaxillary teeth bearing only three cusps (vs. premaxillary teeth bearing five cusps in H. elegans ). An elongate dorsal fin has not been mentioned or illustrated in the available descriptions of H. elegans or detected in the analyzed syntypes. The shared color pattern of H. taphorni and H. elegans may be an indicative of a close relationship, but there is presently no cladistic evidence supporting Hemigrammus as a monophyletic unit. Weitzman & Palmer (1997) discussed that H. unilineatus and similar relatives may belong to their rosy tetra clade based on certain aspects of their color pattern, such as a darkened dorsal-fin blotch or area, and supplementary anatomical evidence, such as the sexually dimorphic elongate dorsal fin, both of which are present in H. taphorni . Thus, H. taphorni , as well as H. elegans , should be added to Weitzman & Palmer’s (1997) list of putative members of the rosy tetra clade in future phylogenetic investigations.