Eurycheilichthys apocremnus, 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 : 9-11

Eurycheilichthys apocremnus , new species

urn:lsid:zoobank.org:act:FE8E4E7B-7CBB-4430-A00D-832ED531C10D

Fig. 8; Tabs. 1, 3, 4

Eurycheilichthys sp. 1 .- Reis, Carvalho, 2007: 84 [listed].

Holotype. MCP 40660, 47.0 mm SL, male, Brazil, Rio Grande do Sul, Barros Cassal, creek tributary to rio Fão, rio Taquari basin, ca. 7 km North of Barros Cassal (29º03’09”S 52º34’50”W), 11 Apr 2000, R. E. Reis et al.

Paratypes. Brazil: Rio Grande do Sul: upper rio Taquari drainage: MCP 25678, 10 , 30.8-50.6 mm SL, 2 c&s, 45.1- 45.4 mm SL (9, 38.1-50.6 mm SL), MZUSP 92422 , 3 , 30.5 -50.0 mm SL (2, 41.6-50.0 mm SL), AMNH 238571 , 3 , 31.5-50.2 mm SL (2, 43.9-50.2 mm SL), collected with the holotype. MCP 21544, 2 , 1 c&s, 46.1 mm SL (2, 46.9- 49.0 mm SL), creek tributary to rio Fão, ca. 7 km North of Barros Cassal, Barros Cassal (29º03’09”S 52º34’50”W), 12 Oct 1998, R. E. Reis et al. MCP 35071, 2 (2, 49.9- 54.1 mm SL) and 8 tis, 32.3-50.5 mm SL, arroio Fãozinho near Vila Nova, Barros Cassal (29º02’51”S 52º34’06”W), 21 May 2004, R. E. Reis et al. MCP 35124, 3 tis, 30.7- 36.0 mm SL, creek tributary to arroio Fãozinho near Vila Nova, Barros Cassal (29º02’53”S 52º33’19”W), 21 May 2004, R. E. Reis et al .

Genseq- 2 16S. MCP 35071; GenBank accession number KX355631 .

Genseq-2 COI. Sequences deposited in GenBank by Cristian Cramer for COI ( MCP 35071; GenBank accession number EU370997 ) .

Genseq-4 COI. Sequences deposited in GenBank by Cristian Cramer for COI ( MCP 35124; GenBank accession number EU370996 ) .

Diagnosis. Eurycheilichthys apocremnus is distinguished from E. limulus and E. castaneus , by exhibiting many irregularly shaped dark blotches and spots on the body and head (vs. body and head plain dark brown, without blotches or spots); from E. limulus by exhibiting a wider cleithrum (28.4-31.8 vs. 23.8-26.8% SL); from E. luisae , E. planus , and E. vacariensis by the abdomen being fully covered by small platelets (vs. naked or partially plated with a middle stripe of platelets, or incompletely covered with granular platelets), and by possessing 27-28 (and occasionally 26) plates in the middle lateral series (vs. 23-26 plates); from E. planus , E. coryphaenus , and E. vacariensis by a longer first pelvic-fin ray (20.4-23.3% SL vs. 16.9-20.1 in E. coryphaenus , 15.6- 19.2 in E. planus , and 14.6-20.1 in E. vacariensis ); from E. pantherinus by the lower lip hardly reaching the anterior margin of the pectoral girdle (vs. lower lip clearly extending past the anterior margin of the pectoral girdle), and by the deeper caudal peduncle (10.2-12.3 vs. 7.8-10.2% SL); from E. planus by the deeper caudal peduncle (10.2-12.3 vs. 8.9-10.0% SL); from E. coryphaenus by possessing 27-28 (occasionally 26) plates in middle lateral series (vs. 25-26 plates), and the parieto-supraoccipital without a conspicuous elevation (vs. parieto-supraoccipital conspicuously elevated); and from E. paucidens by possessing numerous (27-38) accessory teeth on premaxilla in several irregular series (vs. fewer, 2-10 accessory teeth on premaxilla in one irregular series).

Description. Proportional measurements and counts in Tabs. 1, 3, and 4. Dorsal body profile gently arched from snout tip 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 parieto-supraoccipital or dorsal-fin origin. Head and snout broad, flat, and rounded anteriorly; body progressively narrowing caudally from cleithrum. Interorbital space slightly convex; superior margin of orbits slightly elevated. Snout 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 9.5-14.2% HL, dorsolaterally placed.

Pectoral fin of moderate size, spine strongly arched. Posterior fin margin straight or slightly rounded and 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, extending to anal-fin origin. Males possess well developed fleshy flap along posterodorsal margin of thickened first pelvic-fin ray. Dorsal-fin origin at vertical line through end of pelvic-fin base; reduced and plate-like spinelet present; dorsal-fin locking mechanism non-functional. Adipose fin absent.

Body entirely covered by dermal plates except for area around anus, opening of swimbladder capsule posterovental 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, covered medially by skin and 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. 2c). Posterior tip of parieto-supraoccipital with small patch of enlarged but not raised odontodes compared to those of 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 end of canal-bearing lateral cheek plate or between that point and anterior margin of pectoral girdle. Lower lip margin 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 tan to light brown with many dark brown blotches of irregular shape, larger on caudal peduncle; marks on head coalesced such that lighter lines appear especially on snout and cheeks; yellowish tan, mostly unpigmented ventrally. Hypertrophied odontodes on tip of parieto-supraoccipital bone lighter than background. First thickened ray of dorsal, pectoral, pelvic, and anal fins and external rays of caudal fin with chromatophores arranged in two or three discernible blotches. Branched rays in these fins with similar color pattern. Caudal fin primarily dark brown with light middle vertical band.

Distribution and habitat. Eurycheilichthys apocremnus is only known from three localities in the upper reaches of rio Fão, a tributary to the rio Forqueta, rio Taquari basin, Rio

Grande do Sul, Brazil ( Fig. 7). The localities are in a small creek with fast flowing clear water and a substrate covered with rocks and stones.

Etymology. The specific epithet of Eurycheilichthys apocremnus is from the Greek apo, meaning from, and kremnos, meaning cliff or precipice, in allusion to the steep landscape of the type locality.An adjective in the nominative.

Conservation status. Eurycheilichthys apocremnus is not abundant and is only known from three sites in one creek tributary to the arroio Fãozinho, with Extent of Occurrence (EOO) of approximately 0.37 km 2 and Area of Occupancy (AOO) of approximately 0.05 km 2, estimated considering the 14 km of creek extension and an average of 4 m width. In addition,collectingattemptsinthelowerportionoftheFãozinho revealed the presence of E. luisae , which is probably replacing E. apocremnus downstream. Since the species is found only in that creek and intense agriculture occurs in the area, the creek is considered as one location and a continuing decline in habitat quality is inferred. Based on the above evidence E. apocremnus can be categorized as Critically Endangered (CR) by the IUCN criteria B1B2ab(iii); D2 (IUCN, 2016).