Eurycheilichthys planus, 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 : 22-24

Eurycheilichthys planus , new species

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Fig. 14; Tabs. 2-4

Eurycheilichthys sp. 3 .- Reis, Carvalho, 2007: 84 [listed].

Holotype. MCP 40663, 49.3 mm SL, male, Brazil, Rio Grande do Sul, Guabiju, rio da Prata at Passo do Respraiado, rio Taquari basin, on road from Guabiju to André da Rocha (28º38’04”S 51º36’53”W), 20 Jan 1999, R. E. Reis et al.

Paratypes. Brazil: Rio Grande do Sul: upper Rio Taquari drainage: MCP 22199, 176 , 14.3 - 50.2 (3, 44.3-45.2 mm SL), MZUSP 92425 , 10 , 22.6-50.3 mm SL, AMNH 238574 , 10 , 26.3-47.4 mm SL, UFRGS 8483 , 10 , 26.6- 45.4 mm SL, collected with the holotype. MCP 22122, 22 , 34.8-55.1 mm SL (4, 43.1-55.1 mm SL), arroio Herval, between Nova Prata and Guabiju, Guabiju (28º39’35”S 51º37’05”W), 20 Jan 1999, R. E. Reis et al. MCP 40941, 12 , 30.4-49.1 mm SL, arroio Herval, between Nova Prata and Guabiju, Guabiju (28º39’33”S 51º37’03”W), 24 Oct 2006, T. P. Carvalho & V. A. Bertaco. MCP 35041, 7 , 35.8- 56.6 mm SL (3, 43.8-56.6 mm SL), 9 tis, 43.2-57.0 mm SL, arroio Herval, between Nova Prata and Guabiju, Guabiju (28º39’35”S 51º37’05”W), 22 May 2004, R. E. Reis et al. MCP 35062, 25 , 22.6-46.2 mm SL (3, 41.7-46.2 mm SL), rio da Prata at Passo do Respraiado , on road from Guabiju to André da Rocha , Guabiju (28º38’04”S 51º36’53”W), 22 May 2004, R. E. Reis et al. MCP 22261, 41 , 31.7-50.4 mm SL, 2 c&s, 42.2-46.9 mm SL (3, 41.4-50.4 mm SL), arroio Água Branca at Água Branca, ca. 20 km N of Nova Prata, Guabiju (28º36’27”S 51º37’15”W), 20 Jan 1999, R. E. Reis et al. MCP 40930, 25 , 29.9-45.4 mm SL, rio da Prata at Passo do Respraiado , on road from Guabiju to André da Rocha , Guabiju (28º38’01”S 51º36’51”W), 24 Oct 2006, T. P. carvalho & V. A. Bertaco .

Genseq- 2 16S. MCP 35041; GenBank accession number KX355635 .

Genseq-2 COI. Sequences deposited in GenBank by Cristian Cramer for COI ( MCP 22199; GenBank accession number EU370991 ).

Non-types. Brazil: Rio Grande do Sul: upper Rio Taquari drainage: MCP 35062, 33 tis, 23.0- 43.2 mm SL, rio da Prata at Passo do Respraiado, on road from Guabiju to André da Rocha , Guabiju (28º38’04”S 51º36’53”W), 22 May 2004, R. E. Reis et al .

Diagnosis. Eurycheilichthys planus is distinguished from all congeners by its naked abdomen (vs. abdomen fully covered by small platelets in most species, or with a midventral row of platelets in E. luisae and E. vacariensis ), and by having the posterior portion of the head and the predorsal region distinctly flat (vs. head and predorsal region elevated posterior to orbits). It is further distinguished from E. luisae by the lower caudal peduncle length (8.9-10.0 vs. 10.1- 12.5% SL), and by the shorter lower lip not extending to the anterior margin of the pectoral girdle (vs. large lower lip, extending past the anterior margin of the pectoral girdle). Eurycheilichthys planus is further distinguished from E. castaneus by possessing 24-26 plates in middle lateral series (vs. 27-29 plates), and a shorter anal-fin spine (13.9-17.0 vs. 17.6-22.1% SL); from E. limulus by possessing 24-26 plates in the middle lateral series (vs. 27-28 plates) and by having the body and head with dark blotches and spots (vs. body and head plain dark brown, without blotches or spot, and with thin light stripes from snout tip, crossing above the eye and predorsal area); from E. apocremnus by possessing 24-26 plates in middle lateral series (vs. 26-30 plates, occasionally 26), by possessing a shorter pelvic-fin spine (15.6-19.2 vs. 20.4-23.3% SL), shorter anal-fin spine (13.9- 17.0 vs. 18.3-22.1% SL), and narrower caudal peduncle (8.9-10.0 vs. 10.2-12.3% SL); from E. coryphaenus by the parieto-supraoccipital lacking conspicuous elevation (vs. parieto-supraoccipital conspicuously elevated), shorter dorsal-fin spine length (16.5-21.6 vs. 21.8-24.0% SL), and flatter head (depth 41.6-46.9 vs. 47.8-54.0% SL); and from E. paucidens by possessing a shorter first pelvic-fin ray (15.6-19.2 vs. 19.4-24.2% SL), shorter first anal-fin ray (13.9-17.0 vs. 18.2-22.2% SL), larger orbital diameter (12.4-14.0 vs. 9.3-12.4% HL), 24-26 plates in middle lateral series (vs. 26-30 plates, rarely 26), and more numerous (26- 37) accessory teeth on the premaxilla in several irregular series (vs. fewer, 2-10 accessory teeth on premaxilla in one irregular series).

Description. Proportional measurements and counts in Tabs. 2, 3, and 4. Dorsal body profile straight to slightly arched from snout tip to orbits; straight to slightly arched from that point to dorsal-fin origin; parieto-supraoccipital bone and predorsal area wide and flat, especially in larger individuals. 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 rounded anteriorly, with body progressively narrowing caudally from cleithrum. Interorbital space flat; superior margin of orbits not elevated. Snout convex anterior to nares. Nostrils at posterior terminus of pair of elongate, shallow depressions beginning close to snout tip. Eye comparatively small, orbit diameter 12.4-14.9% HL, dorsolaterally placed.

Pectoral fin of moderate size, spine moderately arched, posterior fin-margin rounded; extending to middle of pelvic fin when depressed. Fleshy flap along posterodorsal margin of pectoral-fin spine low 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 slightly shortened compared to that of males, extending to point midway between anus and anal-fin origin when depressed. Males with well-developed fleshy flap along posterodorsal margin of pectoral-fin spine and thickened first pelvic-fin ray. Dorsal-fin origin slightly posterior to vertical line through end of pelvic-fin base; spinelet present, reduced and plate-like; dorsal-fin locking mechanism nonfunctional. Adipose fin absent.

Body entirely covered by dermal plates except for abdominal surface from head to anus, opening of swimbladder capsule posteroventrally to compound pterotic, and surrounding pectoral- and pelvic-fin insertions, and ventral surface of head around lips. Body and head

lacking crests. Coracoid and cleithrum exposed laterally,

covered medially by thick skin. Arrector fossa open. Lateral abdominal plates absent. Middle abdominal plates absent; occasionally few small, granular platelets embedded in skin posteriorly, near pelvic-fin insertions ( Fig. 2h). Posterior tip of parieto-supraoccipital with small patch of enlarged and raised odontodes compared to remainder of head and predorsal area in smaller individuals; absent in large adults. Head and body plates covered with odontodes, being 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, papillose, extending posteriorly to end of canal-bearing lateral cheek plate or extending slightly past that point. Lower lip margin smooth to slightly 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) 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 grayish brown; yellowish tan, mostly unpigmented ventrally. Dorsal surface with many dark, grayish brown, roundish dots scattered throughout head and predorsal area; dots coalesce to form larger blotches on trunk and caudal peduncle. Lateral-line pores relatively unpigmented, forming very thin longitudinal stripe along middle of dark sides of body. First thickened ray of dorsal, pectoral, pelvic, and anal fins and external rays of caudal fin with chromatophores arranged in three to five discernible blotches. Branched rays in these fins with similar color pattern forming bands. Caudal fin hyaline to yellowish tan, with three or four dark irregular vertical bands.

Distribution and habitat. Eurycheilichthys planus is known from few localities in the rio da Prata, a tributary to the rio Turvo - itself a tributary to the rio das Antas, rio Taquari basin, Rio Grande do Sul, Brazil ( Fig. 7). The localities are creeks or small rivers with medium flowing water and a substrate formed by flat rock beds or covered with stones. Large amounts of aquatic macrophytes are present in some areas, though fish are commonly found among the loose stones of the substrate.

Etymology. The specific epithet of Eurycheilichthys planus is from the Latin planus , meaning flat, level, smooth, in allusion to the distinctly flat head and predorsal area. An adjective.

Conservation status. Eurycheilichthys planus is known from two tributary creeks and the upper rio da Prata itself,

with Extent of Occurrence (EOO) of approximately 1.8

km 2. The intense agriculture in the area causes continuing decline in habitat quality but 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).