Eurycheilichthys castaneus, Reis, 2017

Reis, Roberto E., 2017, Unexpectedly high diversity in a small basin: A taxonomic revision of Eurycheilichthys (Siluriformes: Loricariidae), with descriptions of seven new species, Neotropical Ichthyology 15 (1), No. e 160068, pp. 1-28 : 11-13

Eurycheilichthys castaneus , new species

urn:lsid:zoobank.org:act:D9548A02-EE9C-4612-9C35-B8C776C17BE1

Fig. 9; Tabs. 1, 3, 4

Eurycheilichthys sp. 4 .- Reis, Carvalho, 2007: 84 [listed].

Holotype. MCP 40664, 48.1 mm SL, male, Brazil, Rio Grande do Sul, Marau, arroio Burro Preto, tributary to rio Guaporé , rio Taquari basin, on road RS-324, between Passo Fundo and Marau (28º21’29”S 52º15’51”W), 19 Jan 1999, R. E. Reis et al.

Paratypes. Brazil: Rio Grande do Sul: upper rio Taquari drainage: MCP 22134, 13 , 22.9-49.6 mm SL, 2 c&s, 36.3- 47.8 mm SL (7, 40.1-49.6 mm SL), MZUSP 92426 , 2 (2, 37.5-47.4mm SL), AMNH 238575 , 2 (2, 44.3-47.4 mm SL), collected with the holotype. MCP 22270, 4 , 33.7-41.9 mm SL (2, 38.0- 41.9 mm SL), arroio Burro Preto on road to Balneário Capingui , Passo Fundo (28º21’08”S 52º15’56”W), 31 Jan 1999, L. Hahn et al. MCP 22234, 1 (1, 44.0 mm SL), arroio Porongos , ca. 1.5 km NE of Vila Maria, Vila Maria , Marau (28º31’34”S 52º08’22”W), 20 Jan 1999, R. E. Reis et al. MCP 35049, 13 , 27.6-48.2 mm SL (7, 37.2-48.2 mm SL) and 15 tis, 28.6-49.2 mm SL, arroio Burro Preto on road to Balneário Capingui, Passo Fundo (28º21’08”S 52º15’56”W), 22 May 2004, R. E. Reis et al. MCP 35043, 3 (3, 40.2-44.9 mm SL) and 8 tis, 30.1-42.8 mm SL, arroio Porongos at Vila Maria , Marau (28º31’36”S 52º08’37”W), 22 May 2004, R. E. Reis et al .

Genseq- 2 16S. MCP 35043; GenBank accession number KX355632 .

Genseq-4 COI. Sequences deposited in GenBank by Cristian Cramer for COI ( MCP 35049; GenBank accession number EU370999 ) .

Non-types. Brazil: Rio Grande do Sul: upper rio Taquari drainage: MCP 35121, 11 tis, 27.3-47.0 mm SL, arroio Burro Preto , on road RS-324, between Passo Fundo and Marau, Marau (28º21’29”S 52º15’51”W), 22 May 2004, R. E. Reis et al .

Diagnosis. Eurycheilichthys castaneus is distinguished from all congeners, except E. limulus , by possessing a plain dark brown body and head, without blotches or spots, and with thin light stripes from the snout tip, crossing above the eye and predorsal area (vs. body and head with a different combination of dark blotches and spots). It is distinguished from E. limulus by having the upper lobe of the caudal fin plain brown in color (vs. upper caudal-fin lobe primarily hyaline), and the spine and rays of the dorsal fin plain brown (vs. spotted). Eurycheilichthys castaneus is further distinguished from E. coryphaenus , E. luisae , E. pantherinus , E. planus , and E. vacariensis by possessing 27-29 plates in the middle lateral series (vs. 23-26 plates, though one specimen of E. pantherinus had 27 in one side); from E. luisae , E. planus , and E. vacariensis by possessing an abdomen fully covered by small platelets (vs. naked, partially plated with a middle stripe of platelets, or incompletely covered by granular platelets); from E. pantherinus by the lower lip not reaching the anterior margin of the pectoral girdle (vs. lower lip clearly going past the anterior margin of the pectoral girdle); from E. paucidens by possessing more numerous (14-17) accessory teeth on the premaxilla in two or three irregular series (vs. fewer, 2-10 accessory teeth on the premaxilla in one irregular series); and from E. apocremnus by a narrower cleithral width (23.8-26.8 vs. 28.4-31.8% SL).

Description. Proportional measurements and counts in Tabs. 1, 3, and 4. Dorsal body profile gently arched from snout tip to parieto-supraoccipital posterior process; straight to slightly concave from that point to dorsal-fin origin. Trunk generally straight and tapering slightly toward caudal-fin base. Trunk and caudal peduncle rounded in cross section, slightly flattened at and behind base of dorsal and anal fins, and compressed caudally. Greatest body depth at dorsal-fin origin. Head and snout broad and rounded anteriorly, with body progressively narrowing caudally from cleithrum. Interorbital space flat to slightly convex; superior margin of orbits slightly elevated. Snout straight to slightly convex anterior to nares. Nostrils located at posterior terminus of pair of elongate, shallow depressions beginning close to snout tip. Eye comparatively small, orbit diameter 10.8- 14.9% HL, dorsolaterally placed.

Pectoral fin of moderate size, spine moderately arched, posterior fin-margin straight or slightly concave; extending to middle of pelvic fin when depressed. Fleshy flap along posterodorsal margin of pectoral-fin spine in both male and female adults. Pectoral-fin axillary slit present, with large opening ventral to tip of posterior process of cleithrum. Pelvic fin of females short; extending to point midway between anus and anal-fin origin when depressed. Thickened first pelvic-fin ray of males longer, sometimes reaching to anal-fin origin. Males with well-developed fleshy flap along posterodorsal margin of thickened first pelvic-fin ray; females with small, low fleshy flap. Dorsal-fin origin slightly posterior to vertical line through end of pelvic-fin base; spinelet present, reduced and plate-like; dorsal-fin locking mechanism non-functional. Adipose fin absent.

Body entirely covered by dermal plates except for area around anus, opening of swimbladder capsule posteroventrally to compound pterotic, around pectoral- and pelvic-fin insertions, and ventral surface of head around lips. Body and head without crests. Coracoid and cleithrum exposed laterally and covered medially by middle abdominal platelets. Arrector fossa open. Lateral abdominal plates absent. Middle abdominal plates small, irregularly arranged, and covering most of abdominal surface between pectoral girdle and anal opening ( Fig. 2d). Posterior tip of parieto-supraoccipital with small raised patch of larger odontodes than those on remainder of head and predorsal area, especially in smaller individuals. Head and body plates covered with odontodes, these larger on ventral face of pelvic and pectoral spines. Odontodes on head and trunk otherwise of uniform size and distribution, not arranged in conspicuous rows.

Lips roundish and wide, papillose, extending posteriorly to point between end of canal-bearing lateral cheek plate and anterior margin of pectoral girdle. Lower lip margin fringed. Maxillary barbel short, mostly adnate to lower lip. Teeth slender, bifid; major (medial) cusp large, bladelike, and slightly rounded; minor (lateral) cusp minute, pointed. Accessory patch of unicuspid teeth on premaxilla and dentary, attached to dermal bone posterior (premaxilla) and anterior (dentary) to margin of tooth cup, which encloses main series of emergent and pre-emergent bifid teeth. Accessory teeth elongate, sharply pointed, directed posteroventrally (premaxilla) and anteroventrally (dentary).

Color in alcohol. Background color of dorsal surface of head and body dark grayish brown; yellowish tan, primarily unpigmented ventrally. Inconspicuous longitudinal light stripes on each side, beginning on snout tip, crossing between nostrils and orbits on each side, becoming fainter and disappearing on predorsal area. Hypertrophied odontodes on tip of parieto-supraoccipital bone lighter than background. Opercle with small lighter spot. All fin rays dark brown, without concentrated chromatophores. Interradial membranes mostly hyaline.

Distribution and habitat. Eurycheilichthys castaneus is known from a few localities in the upper reaches of rio Guaporé basin, a tributary to the rio Taquari, Rio Grande do Sul, Brazil ( Fig. 7). The localities are small creeks with medium to fast flowing clear water and a substrate covered with rocks and stones. Fishes were collected among rocks only.

Etymology. The specific epithet of Eurycheilichthys castaneus is from the Latin castaneus , meaning brown, chestnut colored, in allusion to the primarily plain dark brown color. An adjective.

Conservation status. Eurycheilichthys castaneus is relatively abundant in tributaries to the upper rio Guaporé, with Extent of Occurrence (EOO) of approximately 110 km 2. Despite the continuing decline in habitat quality because of land use change, especially agriculture, the population is neither severely fragmented nor presenting extreme fluctuations, and the species can be categorized as Near Threatened (NT) according to IUCN criteria B1b(iii) (IUCN, 2016).