Unexpectedly high diversity in a small basin: A taxonomic revision of Eurycheilichthys (Siluriformes: Loricariidae), with descriptions of seven new species

A taxonomic revision of Eurycheilichthys is provided, and seven new species are described in addition to the two previously known species in this genus: E. pantherinus from the upper rio Uruguay, and E. limulus from the upper rio Jacuí. The genus is diagnosed based on the uniquely derived presence of seven branched pectoral-fin rays, and on the possession of reduced filamentous gill rakers in the oral surface of the hyobranchial skeleton, and presence of a distinct fleshy flap along the posterodorsal margin of the pectoral-fin spine in adult males. The seven new species are described from tributaries to the rio Taquari basin, itself a tributary to the rio Jacuí in Rio Grande do Sul State, southern Brazil. The new species are diagnosed based on color variation, abdominal plate morphology, lip size, parieto-supraoccipital shape, the number of dermal plates, the number of teeth, and body proportions. The high diversity and degree of species endemism in a limited area are discussed and compared to other fish groups. Genetic sequences (GenSeq) of mitochondrial and nuclear DNA, distribution maps, an identification key, and illustrations are presented for all species.


Introduction
Eurycheilichthys Reis & Schaefer, 1993 is a member of the loricariid subfamily Hypoptopomatinae, and is composed of small size cascudinhos that live among rocks of fast flowing creeks and rivers in southern Brazil.The genus was originally described as a replacement name for Eurycheilus Reis & Schaefer, 1992 -a name discovered to be preoccupied by a fossil cephalopod soon after its description.The type species, E. pantherinus, from the upper reaches of the rio Uruguay in southern Brazil, was also described in Reis, Schaefer (1992).A few years later, Reis, Schaefer (1998) described a second species of Eurycheilichthys, E. limulus, from two localities in the upper portion of the rio Jacuí, main tributary to the laguna dos Patos system in Rio Grande do Sul State, South Brazil.
Eurycheilichthys was originally diagnosed by Reis, Schaefer (1992) based on the possession of a greatly expanded lower lip, the presence of seven branched rays in the pectoral fin, the accessory ceratobranchial flange reduced to a small, slender uncinate process, the loss of the filamentous gill rakers from the oral surfaces of the hyobranchial skeleton, and the possession of a very wide body.Of all these features, only the presence of seven branched pectoral-fin rays, instead of the typical six, remained as a uniquely-derived synapomorphy for the genus following the discovery of E. limulus.The accessory ceratobranchial flange is normally developed in E. limulus and in the seven additional new species described in the present study -its reduction becoming a trait diagnostic of E. pantherinus alone.The filamentous gill rakers on the oral surfaces of the hyobranchial skeleton are in fact absent in E.

e160068[2]
pantherinus, though are present in all other Eurycheilichthys species.Nevertheless, filamentous gill rakers are highly reduced in all species of Eurycheilichthys, and this reduction itself remains a diagnostic trait for the genus.Eurycheilichthys pantherinus shares a wide body with at least three other new species, though broad variation in this feature precludes its use as a reliable distinguishing feature.Finally, E. pantherinus shares a greatly expanded lower lip with at least one of the new species, though a wide range of variation exists in this feature among the seven species being described in the present study.Nevertheless, despite not being shared by all species, the broad and posteriorly expanded lower lip -which in some cases extends beyond the anterior margin of the pectoral girdle -remains an auxiliary feature distinguishing Eurycheilichthys.Moreover, the presence of a distinct fleshy flap along the posterodorsal margin of the pectoral-fin spine in adult males (and females of some species; Fig. 1) represents a novel derived character useful for distinguishing the species of Eurycheilichthys within the hypoptopomatines.
In the years following the discovery and description of Eurycheilichthys limulus, several collecting expeditions were conducted by the Museu de Ciências e Tecnologia of the Pontifícia Universidade Católica do Rio Grande do Sul (MCP) in the upper reaches of the rio Taquari basin, the main tributary to the rio Jacuí.Those expeditions discovered much previously undetected diversity within Eurycheilichthys, and recognized seven additional new species occurring in small rivers and creeks located above 400 m in altitude; the present study describes these seven species.

Material and Methods
The methodology and terminology for linear measurements in the present study follow Pereira et al. (2007), while body plate counts and nomenclature follow Schaefer (1997).Morphological measurements were taken point-to-point to the nearest 0.1 mm with digital calipers under a dissecting scope.
Measurements of bilaterally symmetrical features were taken on the left side of the body whenever possible.Morphometric data are expressed as a percentage of the standard length (SL), with the exception of subunits of the cephalic region, which were expressed as a percentage of the head length (HL).Vertebral counts include the five centra modified into the Weberian apparatus, and the compound caudal centrum (PU1+U1) counted as one element.Vertebral elements and accessory teeth were counted in cleared and stained specimens only.Osteological examinations were performed on specimens cleared and double-stained for bone and cartilage (c&s) according to the procedure of Taylor, Van Dyke (1985).
The Unified Species Concept was employed in the present study (Queiroz, 2007), in which species are equated with independently evolving metapopulation lineages.In the absence of a phylogeny for Eurycheilichthys, consistent morphological difference among separate populations was used as a proxy for lineage independence.In the lists of material examined, museum abbreviations and catalog numbers are presented first, followed by the number of specimens examined and their size range, the number of specimens in different preparations (c&s or tissue samples vouchers originally preserved in absolute ethanol, marked as "tis"), if any, and the number of specimens measured for morphometric comparisons and their size range in parentheses.Locality, date of collection, and collector names follow the aforementioned information.
Genetic sequences from selected type specimens follow GenSeq nomenclature (Chakrabarty et al., 2013).Total genomic DNA was extracted using the DNeasy blood and tissue extraction kit (Qiagen) from muscle samples fixed in 95% ethanol and stored at -20°C.DNA sequences of the mitochondrial 16S gene were amplified by PCR using 8 µl of Qiagen MasterMix, 1.25 µl of each 16S-AR and 16S-BR primers, and 2 µl of DNA template under the following protocol: an initial denaturation step of 3 minutes at 94°C followed by 35 cycles of 94°C for 1 min, annealing at 48°C for 1 min, and extension at 72°C for 1 min, followed by a final 3 min extension step at 72°C.PCR products were purified and sequenced at Macrogen Inc., South Korea.
Following the list of paratypes, additional specimens are listed as non-types for some species.Specimens were excluded from the type series for different reasons including poor state of preservation, inadequate size range, or due to an excessive number of specimens.None of these specimens were utilized in the characterization or description of new species in this study.The following institutions provided material for this study: The American Museum of Natural History, New York (AMNH); Fundación Miguel Lillo, Tucumán (CI-FML); Museu de Ciências Naturais da Fundação Zoobotânica do Rio Grande do Sul, Porto Alegre (MCN); Museu de Ciências e Tecnologia, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre (MCP); Museu Nacional, Rio de Janeiro (MNRJ); Museu de Zoologia da Universidade de São Paulo, São Paulo (MZUSP); Departamento de Zoologia, Universidade Federal do Rio Grande do Sul (UFRGS).Type species.Eurycheilichthys pantherinus (Reis & Schaefer, 1992), by original designation.Body width at anal fin 11.5 14.6 12.8 11.2 14.5 13.1 12.8 12.0 14.0 12.9 12.5 11.9 13.9 12.9 12.9 12.2 13.9  Diagnosis.Eurycheilichthys limulus is distinguished from all congeners by having the pectoral girdle widely exposed ventrally (Fig. 2b;vs. pectoral    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.

Diagnosis
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 11 e160068 [11] 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, collecting attempts in the lower portion of the Fãozinho 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).

Eurycheilichthys castaneus, new species
urn:lsid:zoobank.org:act:D9548A02-EE9C-4612-9C35-B8C776C17BE1Paratypes.Brazil: Rio Grande do Sul: upper rio Taquari drainage: MCP 22134, 13,2 c&s, 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 pectoraland 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.
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).

Diagnosis.
Eurycheilichthys coryphaenus is distinguished from all congeners by having the parieto-supraoccipital conspicuously elevated (Fig. 3) (vs.parieto-supraoccipital without a conspicuous elevation); and the abdominal plates granular and partially embedded in skin such that mostly only odontodes are visible (vs.abdominal plates absent or large and conspicuous).Eurycheilichthys coryphaenus is further distinguished from E. castaneus and E. limulus by the spotted pattern of its body and fins (vs.body plain dark brown, without blotches or spot, and with a light stripe from snout tip, crossing above the eye and predorsal area), and 25-26 plates in middle lateral series (vs.27-29 plates); from E. planus, E. luisae, and E. vacariensis by having the abdomen completely covered by small platelets (vs.naked, partially plated with a middle stripe of platelets, or incompletely covered with granular platelets); from E. planus by the longer dorsal-fin spine (21.8-24.0 vs. 16.5-21.6%SL) and deeper head (47.8-54.0 vs. 41.6-46.9%HL); from E. paucidens and E. apocremnus by the shorter pelvic-fin spine (64.4-80.2 vs. 80.6-100.6% of the pectoralfin spine) and 25-26 plates in middle lateral series (vs.27-30 plates, occasionally 26); from E. paucidens by larger orbital diameter (13.8-18.5 vs. 9.3-12.4%HL); and 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).
Description.Proportional measurements and counts in Tabs. 1, 3 and 4. Dorsal body profile straight to gently arched from snout tip to parieto-supraoccipital, straight from that point to dorsal-fin origin; parieto-supraoccipital with conspicuous elevation, more salient 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 parieto-supraoccipital bone or dorsal-fin origin.Head and snout broad and rounded anteriorly, with body progressively narrowing caudally from cleithrum.Interorbital space flat to slightly concave; superior margin of orbits slightly elevated.Snout flat to slightly convex anterior to nares.Nostrils located at posterior terminus of pair of elongate, shallow depressions beginning close to snout tip.Eye comparatively large, orbit diameter 13.8-18.5%HL, dorsolaterally placed.
Pectoral fin of moderate size, spine slightly arched, posterior fin-margin straight to slightly rounded; extending to between middle and distal third of pelvic fin when depressed.Fleshy flap along posterodorsal margin of pectoral-fin spine low in adult males, and absent in females.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 analfin origin when depressed.Thickened first pelvic-fin ray of males longer, typically extending to anal-fin origin.Males with well-developed fleshy flap along posterodorsal margin of thickened first pelvic-fin ray.Dorsal-fin origin at or slightly posterior to vertical line through end of pelvicfin 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, covered medially by skin and few isolated platelets.Arrector fossa open.Lateral abdominal plates absent.Middle abdominal plates granular and somewhat embedded in skin, irregularly arranged and interspaced, covering most of abdominal surface between pectoral girdle and anal opening (Fig. 2e).Posterior tip of parietosupraoccipital with conspicuous patch of enlarged and 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 e160068 [15] head and trunk otherwise of uniform size and distribution, not arranged in conspicuous rows.
Lips roundish and wide, papillose, extending posteriorly to a 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 to (dentary) margin of tooth cup, which encloses main series of emergent and pre-emergent bifid teeth.Accessory teeth large, elongate, sharply pointed, directed posteroventrally (premaxilla) and anteroventrally (dentary).
Color in alcohol.Background color of dorsal surface of head and body tan to brown with few large, dark brown spots throughout head and body; yellowish tan, mostly unpigmented ventrally.Head primarily dark, predorsal region lighter; two inconspicuous lighter saddles on dorsum, at end of dorsal-fin base and caudal peduncle.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 four to six discernible blotches.Branched rays in these fins with similar color pattern.Caudal fin with three or four irregular dark vertical bands.

Distribution and habitat.
Eurycheilichthys coryphaenus is known from localities in the upper reaches of the rio Tainhas basin, which is a tributary to the rio das Antas, rio Taquari basin, Rio Grande do Sul, Brazil (Fig. 11), an area located at the extreme eastern headwaters of the rio Taquari basin, in the Araucaria forest area.One lot from rio Tomé (UFRGS 5077) is tentatively assigned to this species and specimens are considered non-types.The localities are small creeks with medium flowing clear water and substrate covered with rocks and stones.Despite dense vegetation including marginal grasses and aquatic macrophytes being present in these localities, fishes are found dwelling among loose stones on the substrate.
Etymology.The specific epithet of Eurycheilichthys coryphaenus is from the Greek koryphe, meaning head, crown, top, or highest point, in allusion to the distinctly elevated parieto-supraoccipital bone.An adjective.

Eurycheilichthys luisae, new species
e160068 [19] Body entirely covered by dermal plates except for area around anus, opening of swimbladder capsule posteroventrally to compound pterotic, most of the abdomen, and ventral surface of head around lips.Body and head without crests.Coracoid and cleithrum exposed laterally, covered medially by skin and few isolated platelets.Arrector fossa open.Lateral abdominal plates absent.Middle abdominal plates small to granular, irregularly arranged in a middle patch in front of the anal opening that can extend to anterior portion of abdomen, leaving large unplated areas laterally (Fig. 2f).Posterior tip of parieto-supraoccipital with small 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 first pelvic-fin ray and pectoral spine.Odontodes on head and trunk otherwise of uniform size and distribution, not arranged in conspicuous rows.
Lips roundish and wide, papillose, and extending posteriorly to a point between of canal-bearing lateral cheek plate and anterior margin of pectoral girdle.Lower lip margin smooth to 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 large, elongate, sharply pointed, directed posteroventrally (premaxilla) and anteroventrally (dentary).
Color in alcohol.Background color of dorsal surface of head and body light brown with many roundish dark brown dots scattered throughout head and body; dots smaller and more concentrated on head; yellowish tan, mostly unpigmented ventrally except for caudal peduncle.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 three or four discernible blotches.Branched rays in these fins with similar color pattern.Caudal fin mostly primarily dark brown, with three or four light irregular vertical bands.

Distribution and habitat.
Eurycheilichthys luisae is known from several localities in both the upper and lower courses of the rivers Forqueta, Carreiro, Turvo, and the rio das Antas -all tributaries to the rio Taquari, Rio Grande do Sul, Brazil (Fig. 11).All localities are creeks or rivers with medium to fast flowing water and substrate covered with rocks and stones.Fish are commonly found among the loose stones on the substrate.
Etymology.Eurycheilichthys luisae is named in honor of my daughter Luisa F. Reis, who loves nature and occasionally assisted on weekend field trips for collecting specimens.A noun in the genitive case.
Conservation status.Eurycheilichthys luisae is frequent and abundant in the upper rio Taquari basin.Despite the Extent of Occurrence (EOO) is approximately 7,700 km 2 and hydroelectric dams exist and are planned in that basin, no specific threats were detected, and the species can be categorized as Least Concern (LC) according to IUCN criteria (IUCN, 2016).

Diagnosis.
Eurycheilichthys paucidens is distinguished from all congeners by possessing few (2-10) accessory teeth on the premaxilla in one irregular series (vs.numerous, 14-62 accessory teeth on the premaxilla in two to several irregular series).It is also distinguished from five other species by the relatively small orbital diameter 5 in E. luisae), and by possessing 27-29 (one specimen with 26 on one side) plates in middle lateral series (vs.23-26 in E. coryphaenus, E. pantherinus (one specimen with 27 in one side), E. planus, E. vacariensis and E. luisae).Eurycheilichthys paucidens is further distinguished from E. limulus and E. castaneus by exhibiting many dark, irregularly shaped blotches and spots on the body and head (vs.body and head plain dark brown without blotches or spots); from E. planus by the longer pelvic-fin spine (19.4-24.2 vs. 15.6-19.2%SL) and longer anal-fin spine (18.2-22.2 vs. 13.9-17.0%SL); and from E. luisae by the shorter mandibular ramus (7.0-10.8 vs. 11.1-14.7%HL).

Description. Proportional measurements and counts in
Tabs. 2, 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 located at dorsal-fin origin.Head and snout broad and flat, rounded anteriorly; body progressively narrowing caudally from cleithrum.Interorbital space flat to 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 very small, orbit diameter 9.3-12.4%HL, dorsolaterally placed.
Pectoral fin of moderate size, spine strongly arched, posterior fin-margin straight or slightly concave; extending to middle to second third 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, slightly extending past anal-fin origin.Males with welldeveloped fleshy flap along posterodorsal margin of thickened first pelvic-fin ray; females exhibit smaller flap.Dorsal-fin origin slightly posterior to vertical line through end of pelvic-fin base; spinelet present, reduced and platelike; 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 pectoraland pelvic-fin insertions, and ventral surface of head around lips.Body and head lacking 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. 2g).Posterior tip of parietosupraoccipital lacking a conspicuous patch of enlarged odontodes.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, with posterior margin falling short of or extending posteriorly to end of canal-bearing lateral cheek plate.Lower lip margin smooth.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 and very small, arranged in single series and 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; head 22 e160068 [22] primarily dark with thin lighter lines, especially on snout and cheeks; yellowish tan, mostly unpigmented ventrally.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 variably spotted, with middle light vertical band and lighter distal half.
Distribution and habitat.Eurycheilichthys paucidens is known from various tributaries to the rio Turvo and rio das Antas, of the rio Taquari basin, Rio Grande do Sul, Brazil (Fig. 11).All localities are creeks or small rivers with medium to fast flowing water and substrate covered with rocks and stones.Fish are commonly found among the loose stones on the substrate.
Etymology.The specific epithet of Eurycheilichthys paucidens is from the Latin paucus, meaning few, little, and dens, meaning tooth, in allusion to the small number of accessory teeth in both premaxilla and dentary.An adjective in the nominative.
Conservation status.Eurycheilichthys paucidens is frequent and moderately abundant in the upper rio Taquari basin.Despite the Extent of Occurrence (EOO) is approximately 7,500 km 2 and hydroelectric dams exist and are planned in that basin, no specific threats were detected, and the species can be categorized as Least Concern (LC) according to IUCN criteria (IUCN, 2016).

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 ; 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 , shorter anal-fin spine , 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 , shorter first anal-fin ray , 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 e160068 [24] 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).
Description.Proportional measurements and counts in Tabs.2, 3, and 4. Dorsal body profile gently arched from snout tip to parieto-supraoccipital bone, straight to slightly arched from that point to dorsal-fin origin.Trunk generally straight and tapering slightly to 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 from cleithrum to caudal peduncle.Interorbital space flat to 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 to medium, orbit diameter 12.5-16.9%HL, dorsolaterally placed.
Pectoral fin of moderate size, spine moderately arched, posterior fin-margin rounded; reaching from half to twothirds length 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 short, reaching to point midway between anus and anal-fin origin when depressed.Thickened first pelvic-fin ray of males slightly longer, falling short of anal-fin origin.Males with well-developed Body entirely covered by dermal plates except for area around anus, opening of swimbladder capsule posteroventrally to compound pterotic, around pectoraland pelvic-fin insertions, and ventral surface of head around lips.Body and head lacking crests.Coracoid and cleithrum exposed laterally, covered medially by skin or few isolated platelets.Arrector fossa open.Lateral abdominal plates absent.Middle abdominal plates few and granular, typically arranged longitudinally on middle of abdomen, though sometimes covering most of abdominal surface between pectoral girdle and anal opening (Fig. 2i).Posterior tip of parieto-supraoccipital with small patch of enlarged odontodes compared to 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, and extending posteriorly to end of canal-bearing lateral cheek plate or between that point and anterior margin of pectoral girdle.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 all over head and occasionally predorsal area; dots coalesce into larger blotches on trunk and caudal peduncle.Dorsum with four inconspicuous dark saddles: first on dorsal-fin origin, second posterior to dorsalfin base, and two on caudal peduncle.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 vacariensis is known from localities in the upper reaches of rio Turvo, a tributary to the rio das Antas, rio Taquari basin, Rio Grande do Sul, Brazil (Fig. 7) -an area located at the extreme northern headwaters of the rio Taquari basin.One population from the rio Atanásio in the rio Guaporé basin differs slightly in color pattern from those in the rio Turvo basin and this population is excluded from the type series.The localities are small creeks with medium flowing water and substrate covered with rocks and stones.
Etymology.Eurycheilichthys vacariensis is named after the town of Vacaria, a historical place in the highlands of Rio Grande do Sul that exemplifies the traditional Gaucho culture of the region in which this species occurs.
Conservation status.Eurycheilichthys vacariensis is relatively frequent and moderately abundant in the upper rio Turvo basin.Despite the small Extent of Occurrence (EOO) of approximately 2,700 km 2 , no specific threats were detected, and the species can be categorized as Least Concern (LC) according to IUCN criteria (IUCN, 2016).

Discussion
Eurycheilichthys presents high species diversity in a limited geographic area, with nine species inhabiting the headwaters of two river basins in the southern portion of the Araucaria forest plateau of southern Brazil, in an area of approximately 80,000 km 2 .Eurycheilichthys pantherinus is the most widespread species, occupying more than half of that area in the upper rio Uruguay basin (Fig. 5), while E. limulus is endemic to and the only species found in the upper rio Jacuí basin (Fig. 7).The seven new species described herein, however, occur in the upper rio Taquari basin, itself a tributary to the lower rio Jacuí, but whose headwaters are in close proximity to those of the Jacuí and Uruguay rivers (Figs. 7 and 11) -in an area that barely comprises 20,000 km 2 .
The species of Eurycheilichthys are restricted to river sectors that run on the ancient crystalline rock of the Serra Geral formation at an altitudinal range from approximately 400 to 1,400 meters above sea level, and never reach the lower portion of the rivers.Within the rio Taquari basin, only E. paucidens and E. luisae are somewhat widespread and sympatric to other species, while each of the remaining five species is endemic to a single stream or microbasin.Rivers in the upper rio Taquari basin are particularly high energy streams, with high average declivity and deeply excavated valleys.The shallow, fast-flowing habitats used by Eurycheilichthys are isolated from each other by deeper and wider sectors of the middle or lower course of the rivers, which act as barriers to their dispersal.Considering this distribution pattern, isolation and subsequent diversification must have occurred predominantly by headwater stream captures between the upper tributaries of the Uruguay, Jacuí and Taquari rivers and among streams tributary of the rio Taquari themselves.
The aforementioned pattern of species distribution, however, is apparently contrary to the pattern observed in other recently studied fish groups.While only E. pantherinus 27 e160068 [27] occurs along most of the upper rio Uruguay, five species of Hisonotus (Loricariidae; Carvalho, Reis, 2009), seven species of Rineloricaria (Loricariidae; Ghazzi, 2008), 11 species of Crenicichla (Cichlidae; Lucena, Kullander, 1992), and four species of Australoheros (Cichlidae; Říčan, Kullander, 2006;2008) are found in the same area.On the other hand, while seven species of Eurycheilichthys occur in the rio Taquari basin, only Hisonotus carreiro and H. prata are endemic to that region.Two widespread species: H. vireo and H. armatus also occur there as part of their wider distributions (Carvalho, Reis, 2011).Moreover, five species of Rineloricaria occur in the area occupied by Eurycheilichthys as part of their broader distributions (Rodriguez, Reis, 2008), while Crenicichla lucenai is endemic to a tributary of rio Taquari and two other species occur there as part of their broader distribution (Mattos et al., 2014).Only Australoheros taura is present in the rio Taquari basin (Ottoni, Cheffe, 2009).
The upper rio Uruguay basin has been severely altered by a series of large hydroelectric dams for many years, which has significantly impacted most large-sized, migratory species.This seems not to be the case of Eurycheilichthys pantherinus, which is restricted to creeks and headwater streams that are usually unaffected by the reservoirs.The same situation appears to occur with E. limulus in the upper rio Jacuí basin, where at least three large hydroelectric dams are in place in the rio Jacuí itself, while the fish population apparently remains healthy and survives in the headwater streams.In the rio Taquari basin, however, several smallscale dams are being planned or constructed in the tributary rivers, which have the potential to be very harmful to Eurycheilichthys populations, especially those species with very small distributions.If proper care is not taken, the construction of hydroelectric dams could easily bring some of these species to extinction.
Eurycheilus pantherinusReis & Schaefer, 1992: 217, figs.1-5.Type locality: Brazil: Rio Grande do Sul, creek tributary of rio dos Touros, at road from Silveira to Rondinha, Bom Jesus, rio Uruguay basin, approx.28°42'S50°10'W.Eurycheilichthys pantherinus.-Reis&Schaefer,1993:894(newcombination).thelargerorbitaldiameter,and the presence of numerous (27-51) accessory teeth on the premaxilla in several irregular series (vs.fewer, 2-10 accessory teeth on premaxilla in one irregular series).Eurycheilichthys pantherinus is most commonly found in the upper rio Uruguay basin in the most northeasterly region of Rio Grande do Sul and southern Santa Catarina, Brazil (Fig.5).It also occurs in the upper rio Piratini in Santo Ângelo, rio Buricá in Ijuí, and in the upper rio Uruguay itself and lower courses of its tributaries, as well as the río Yaboti-Guazu, a tributary to the rio Uruguay in Misiones, Argentina (Azpelicueta, Koerber, 2014).This species is likely distributed widely in the upper rio Uruguay basin.Most of the localities are small rivers and creeks with fast flowing clear water with a substrate comprised of rocks and stones.The capture in the mainstream of the rio Uruguay (MCP 21740) was made during a severe drought in which a rocky portion of the river bed was exposed.These fishes are typically associated with the river bottom, dwelling among the stones and rocks.
limulus by the color pattern of its body and head, which are covered by many regular small and roundish dark spots (vs.body and head plain dark brown, without blotches or spot, and possessing a light stripe from the snout tip crossing above the eye and predorsal area); from E. limulus by the wider cleithrum; from E. planus and E. vacariensis by the abdomen being fully covered by small platelets (vs.naked or incompletely covered by granular platelets); from E. apocremnus by a shallower caudal peduncle (7.8-10.2 vs. 10.2-12.3%SL);fromE.coryphaenus by the parieto-supraoccipital lacking a conspicuous elevation (vs.parieto-supraoccipital conspicuously elevated); and from E. paucidens by Conservation status.Eurycheilichthys pantherinus is relatively frequent and abundant in the upper rio Uruguay basin.The species has an Extent of Occurrence (EOO) of approximately 52,600 km 2 and despite many hydroelectric dams exist in that basin, no specific threats were detected, and the species can be categorized as Least Concern (LC) according to IUCN criteria(IUCN, 2016).Tab. 1. Descriptive morphometrics of Eurycheilichthys species.Values are given as percents of standard length or of head length.Hol = holotype.SD = standard deviation.Data in bold are distinguishing features among species.

girdle exposed only laterally; Figs. 2a, c-i), and, except for E. castaneus, by possessing a body and head plain dark brown in color, 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 combination of dark blotches and spots).It is distinguished from E. castaneus by having the upper lobe of the caudal fin mostly hyaline (vs.upper caudal-fin lobe plain brown), and the spine and rays of the dorsal fin spotted (vs.spine and rays of the dorsal fin plain brown).
middle lateral series (vs.23-26 plates); from E. luisae and E. pantherinus by the lower lip not extending to the anterior margin of the pectoral girdle (vs.lower lip clearly extending past the anterior margin of the pectoral girdle) and by a narrower cleithral width (23.8-26.8 vs. 27.3-34.0%SL); from E. coryphaenus by possessing 27-28 plates in middle lateral series (vs.25-26 plates), and by having the parieto-
mm SL),MZUSP 92426, 2 (2,  37.5-47.4mmSL),AMNH238575, 2 (2, 44.3-47.4mmSL),collectedwith the holotype.MCP 22270, 4, 33.7-41.9mmSL (2, 38.0-41.9mmSL), arroio Burro Preto on road to 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, Diagnosis.
Tab. 2. Descriptive morphometrics of Eurycheilichthys species.Values are given as percents of standard length or of head length.Hol = holotype.SD = standard deviation.Data in bold are distinguishing features among species.Frequency distribution of variable counts of Eurycheilichthys species.Premaxillary and dentary teeth, counted in both sides; holotype values are underlined.It is distinguished from E. apocremnus, E. castaneus, E. limulus, and E. paucidens by possessing 23-25 plates in middle lateral series (vs.27-30 plates, occasionally 26).Eurycheilichthys luisae is further distinguished from E. castaneus and E. by the color pattern of its body and a head covered with many Tab. 3. Frequency distribution of variable counts of Eurycheilichthys species.Vertebrae and body plates.* = counted in c&s specimens; ** = Both sides of body counted; holotype values are underlined.margin of the pectoral girdle).It is distinguished from E. pantherinus by having the abdomen partially plated with a middle stripe of platelets (vs.completely covered by small platelets), and by the deeper caudal peduncle (10.1-12.5 vs. 7.8-10.2%SL).It is also distinguished from all congeners, except E. planus and E. vacariensis, by an abdomen partially plated with a middle stripe of platelets (vs.abdomen fully covered by small platelets).