Chinchaysuyoa labiata (Boulenger 1898)

Figure 4, 5, 6 and Table 1

Arius labiatus Boulenger 1898:6 (original description; Río Peripa, Ecuador).— Eigenmann 1922:31 (description).— Kailola & Bussing 1995:866 (as status uncertain).— Marceniuk & Ferraris 2003:453 (as species inquirenda).— Betancur-R. & Acero P. 2004:13 (apparently a species of Potamarius).— Marceniuk & Menezes 2007:98 (as species inquirenda in Potamarius).

Hexanematichthys henni Fisher & Eigenmann 1922:30 (original description; Río Daule, Colimes).— Burgess 1989:168 (as status uncertain).—Kailola & Bussing in Fischer et al. 1995:866 (as status uncertain).— Marceniuk & Ferraris 2003:453 (as species inquirenda).— Betancur-R. & Acero P. 2004:13 (as apparently a species of Potamarius).— Jiménez-Prado et al. 2015:398 (as apparently a species of Potamarius).— Marceniuk & Menezes 2007:98 (as species inquirenda in Potamarius).

Diagnosis. Chinchaysuyoa labiata differs from C. ortegai by finer granulation homogeneously distributed in the cephalic shield (vs. thicker and irregularly distributed in the cephalic shield, especially in the sphenotic, pterotic and parieto-supraoccipital, Figs. 5 and 6), snout pointed anteriorly (vs. truncated anteriorly, Fig. 5), distance between the anterior nostrils 5.1–5.9% SL (vs. 6.3–7.6% SL, Table 1), distance between the posterior nostrils 5.2– 6.2% SL (vs. 6.4–7.5% SL, rarely less than 6.4, Table 1), caudal–fin lobes relatively long, pointed posteriorly (vs. relatively short, rounded posteriorly, Fig. 4).

Description. Morphometric data in Table 1. Head depressed, profile elevated posteriorly, straight at frontal and parieto-supraoccipital area. Snout long and anteriorly pointed. Anterior nostril round, with fleshy edge, posterior nostril covered by flap of skin; nostrils relatively close to one another and distant to orbit, not connected by fleshy furrow. Eye lateral and large; eyes relatively close to one another. Three pairs of moderately long teretiform barbels; maxillary barbel usually reaching gill membrane edge, mental barbels not reaching gill membrane edge. Osseous bridge formed by lateral ethmoid and frontal relatively long and slender, little evident under skin. Cephalic shield exposed, gently granulated; long and moderately large on lateral ethmoid, frontal, and supracleithral areas. Anterior portion of dorsomedial groove of neurocranium fleshy, inconspicuous and not continuous to level of posterior nares; posterior portion of osseous groove shallow, with straight margins, narrowing posteriorly. Parietosupraoccipital process funnel-shaped, long and moderately wide on posterior portion, and profile straight. Nuchal plate crescent-shaped, long and moderately wide.

Mouth subterminal to terminal, moderately large; lower jaw arched. Lips thick, upper lip more thick than lower lip. Vomerine tooth plates absent. One pair of oval shaped accessory tooth plates, very small and transversely elongate and narrow, distant one another, with sharp teeth. Premaxilla with sharp teeth. Dentary separated at midline, with sharp teeth. Gill membranes fused, attached to isthmus. Nineteen acicular gill rakers on first arch, 21–23 spike-shaped gill rakers on second arch. Mesial surfaces of all gill arches with developed gill rakers, lateral and mesial surfaces of first and second gill arches lacking fleshy papillae intercalated with gill rakers.

Body width little wider than depth in pectoral-girdle area, progressively more compressed from pectoral fin to caudal peduncle. Lateral line sloping ventrally on anterior one-third, extending posteriorly to caudal peduncle, bending abruptly onto dorsal lobe of caudal fin. Dorsal-fin spine moderately long and thick; anterior margin with granules on basal two-thirds and distal one-third with serrations; posterior margin smooth on basal one-third and distal two-thirds with serrations. Seven soft dorsal-fin rays. Pectoral-fin spine moderately long, shorter than dorsalfin spine; anterior margin with granules on basal two-thirds and distal one-third with short serrations; posterior margin straight on basal one-fourth, distal three-fourths with serrations. Eleven or twelve soft pectoral-fin rays. Posterior cleithral process exposed, rough and triangular shaped, very long and pointed posteriorly. Pelvic fin deep and moderately long at base, with six rays. Adipose-fin base moderately long, its base about half as long as the anal-fin base. Anal fin deep and moderately long at base, with 17–9 rays and distal margin slightly concave. Caudal peduncle relatively low. Caudal fin forked, dorsal and ventral lobes long, wide and pointed posteriorly; dorsal lobe longer than ventral lobe.

Coloration. In alcohol, brown or dark brown on dorsum, flanks brownish to silvery and white on venter; fins brownish or dark brownish. Maxillary barbel light brownish, mental barbel lighter (Fig. 4a,b).

Distribution and habitat. Chinchaysuyoa labiata is known from middle Río Peripa (holotype of Chinchaysuyoa labiata), middle Río Daule (holotype of H. henni), middle Rio Guayas (paratype of H. henni), and middle Rio Vinces (non-type specimens) all from Guayas Basin. Based on the know distribution of the species, we infer that the distribution of Chinchaysuyoa labiata is restrict to freshwater habitat from west Ecuador (Fig. 7).

Remarks. Arius labiatus was described by Boulenger (1898) based on a single specimen deposited at Museo di Zoologia, Instituto di Zoologia e Anatomia Comparata Universitá di Torino, Italy (holotype, MZUT 1540, Fig. 4a). Subsequently, Eigenmann (1922) described Hexanematichthys henni based on three specimens from Río Daule, Ecuador, considering that “It is possible that these specimens are the young of Arius labiatus, the only known specimen of which is three times as large as our largest”. While the descriptions of both species provide good details on the accessory tooth plates, which have a unique configuration in the ariids from the eastern Pacific, both have been considered as species inquirenda in the recent literature (Kailola & Bussing 1995; Marceniuk & Ferraris 2003; Marceniuk & Menezes 2007), due primarily to the small number of samples available in zoological collections and the lack of taxonomic studies of the ariid catfish of the west coast of South America. Here, Chinchaysuyoa labiata is recognized as a valid species and Hexanematichthys henni (Fig. 4) as its junior synonym, supported by the fine, homogeneous granulation of the cephalic shield (Figs. 4 and 6), the narrow snout, which is pointed anteriorly (Fig. 5), the reduced distance between the nostrils (Table. 1), and the well-developed dorsal and ventral lobes of the caudal fin, which are pointed posteriorly, and permit the differentiation of the species from its congeners in the river basins of Peru.

Material Examined. Type-specimens: Holotype: Arius labiatus MZUT 1540 (1, 475 mm SL), Río Peripa, Ecuador. Holotype: Hexanematichthys henni CAS 60620 (1, 139.3 mm SL), Río Daule, Colimes, western Ecuador. Paratype: Hexanematichthys henni CAS 60621 (2, 113– 25 mm SL), Rio Guayas basin, Rio Daule. Non-Type specimens: MCZ 48771(1, 183 mm SL), Los Rios, Rio Vinces (Rio Nuevo) at Vinces.