Hemipsilichthys nimius, Edson H. L. Pereira, Roberto E. Reis, Pablo F. M. Souza & Henrique Lazzarotto, 2003

Edson H. L. Pereira, Roberto E. Reis, Pablo F. M. Souza & Henrique Lazzarotto, 2003, A new species of the loricariid catfish genus Hemipsilichthys from southern Rio de Janeiro coastal rivers, southeastern Brazil (Teleostei: Siluriformes)., Zootaxa 285, pp. 1-10 : 5-9

Hemipsilichthys nimius new species

(Fig. 1)

Holotype. MCP 33049 , male, 105.1 mm SL; Brazil: Rio de Janeiro: Parati: rio Carrasquinho below the Cachoeira do Toboga , upper Pereque-Acu basin, Penha, ca. 7.5 km West of highway BR101, on road from Parati to Cunha (23º12'51"S 44º47'28"W), 1 Feb 2003, E. H. L. Pereira, R. E. Reis & F. Fernandes.

Paratypes. Brazil: Rio de Janeiro: Parati : MCP 31990 , 11 (6) 45.7-98.1 mm SL; collected with the holotype. MCP 30671 , 9 + 1 c&s (5) 35.9-102.2 mm SL; same locality as holotype, 18 Oct 2002, V. A. Bertaco, J. F. P. Silva & P. Lehmann. MCP 31573 , 1, 48.7 mm SL; rio Taquari at Taquari Village, ca. 2.2 km West of highway BR101 (23º02'29"S 44º41'34"W), 18 Oct 2002, V. A. Bertaco, J. F. P. Silva & P. Lehmann. MNRJ 24909 , 2, 32.5-89.1 mm SL; rio Carrasquinho 800 m above " Poco do Tarzan", upper Pereque-Acu basin , 17 Feb 2003, P.M.Souza, H.L.Almeida, U. Fidélis. MNRJ 24910 , 1, 58.1 mm SL; same locality as MNRJ 24909, 11 Jan 2002, H. Lazzarotto, U. Fidelis, M. L. Rheigantz & A. M. Castro. MNRJ 24911 , 2, 38.8-67.0 mm SL; same locality as MNRJ 24909, 24 Mar 2003, P. F. M. Souza & U. Fidelis. MNRJ 24913 , 6, 22.4-41.8 mm SL; same locality as MNRJ 24909, 18 Apr 2002, P. F. M. Souza, M. L. Rheingantz & T. A. P. Vianna. MNRJ 24912 , 1, 34.4 mm SL, rio Pereque-Acu , Penha , 20 Oct 2002, H.L.Almeida, M.L.Rheingantz, M.C.Matos.

Diagnosis: The new species can be easily distinguished from all remaining congeners by the presence of eight (rarely seven or nine) branched rays in dorsal-fin (vs. seven in all other species), and by possessing the dorsal-fin membrane expanded posteriorly, connecting the proximal half of the last dorsal-fin ray to the dorsum. It is also distinguished from most species, except H. gobio and H. papillatus , by having both teeth cusps equal in size (vs. small lateral cusp or unicuspid teeth in both dentary and premaxilla). From H. gobio and H. papillatus it is further distinguished by the larger orbital diameter 15.3-16.9 % HL (vs. 8.6-11.8 % in H. papillatus and 12.0-14.7 % in H. gobio ), and by having a V-shaped dorsal-fin spinelet (vs. oval in H. gobio and absent in H. papillatus ).

Description: Standard length of measured specimens 55.6 to 105.1 mm. Counts and proportional measurements presented in Table 1. Body short and depressed. Greatest width at cleithrum and progressively narrowing from that point to end of caudal peduncle. Dorsal profile of body gently convex, elevating from snout tip to origin of dorsal fin and then descending to last plate of caudal peduncle. Trunk and caudal peduncle rounded dorsally in cross-section, flattened ventrally and more compressed caudally. Greatest body depth at dorsal-fin origin. Dorsal surface of body completely covered by dermal plates, except for a naked area around dorsal fin base. Ventral surface of head, region from pectoral-fin insertion to anal-fin origin totally naked.

Head broad and moderately depressed. Anterior profile of head rounded in dorsal view. Interorbital space slightly concave, nearly flattened. Three small ridges on dorsal surface of head, one median from snout tip to area between nostrils, and one pair from nostril to posterior margin of orbit. Lateral margin of head covered with minute odontodes, straight or curved posteriorly. Snout in lateral profile gently convex. Eye moderately small (15.3 to 16.9 % HL), dorsolaterally placed. Iris without dorsal flap covering pupil, or some with very small flap. Lips roundish and well developed, occupying most of ventral surface of head. Lower lip almost reaching pectoral girdle and covered with minute papillae anteriorly; papillae larger and more spaced towards margin. Papillate surface of lower lip projecting between dentary and premaxillary rami laterally. Posterior edge of lower lip slightly fringed. Maxillary barbel short and free, not coalesced with lower lip. Upper lip with 1-3 rows of transversally elongate papillae. Teeth long, slender, and bicuspid, both cusps approximately equal in size.

Dorsal fin originating slightly posterior to vertical line passing through pelvic-fin origin; nuchal plate covered by skin, dorsal spinelet V-shaped, and dorsal-fin locking mechanism functional. Tips of posterior dorsal-fin rays extending beyond end of pelvic fin. Dorsal-fin spine somewhat flexible, followed by 8 branched rays (in 31 specimens, 7 in two specimens and 9 in two specimen). Dorsal-fin membrane expanded posteriorly, connecting proximal half of last dorsal-fin ray to dorsum. Adipose-fin present, preceded by 4- 7 median, azygous pre-adipose plates, forming tall ridge between dorsal and adipose fins. Pectoral fin small; with curved and flattened spine, and 6 branched rays. Spine of mature males covered with short and delicate hypertrophied odontodes on anterodorsal margin. Posterior margin of pectoral-fin straight; overlapping pelvic-fin origin when adpressed.

Pelvic-fin moderate in size, with one spine and 5 branched rays, not reaching insertion of anal fin when adpressed. Pelvic-fin spine depressed, covered with minute odontodes ventrally and laterally; dermal flap on its dorsal surface absent. Anal-fin small and rounded with one unbranched and 5 branched rays, originating between end of pelvic fin and end of dorsal-fin rays. First anal-fin unbranched ray without odontodes. Caudal fin margin slightly concave, almost truncate, lower rays slightly longer than upper ones, 14 branched rays.

Color in alcohol: Ground color of dorsal surface of head and body light brown to dark yellowish; pale yellow ventrally. Head, dorsum and flanks covered with many dark brown or grayish brown blotches irregularly sized and shaped, in such a way that irregular paler markings appear all over dorsal surface. Head usually slightly darker than body; with consistent lighter markings on ridges anterior to eyes, on middle ridge anterior to nostrils, and on two small bands bordering naked area on tip of snout. Lateral margin of head, from snout to opercle, also pale yellow. Dorsal and caudal fins plain grayish or sometimes with two or three series of inconspicuous dots aligned to form darker, irregular lines. Pectoral and pelvic fins with dark brown or grayish pigmentation on rays and sometimes on fin membrane, sometimes arranged in two or three inconspicuous lines. Anal fin light, sometimes with dark pigmentation on middle portion of rays; fin membrane always hyaline. Ventral surface of head and body mostly unpigmented, except for some brown, scattered pigmentation on lateral margins of body posterior to pelvic fins, and on upper lip, pigmented as dorsal surface of head.

Color in life: Same pattern as above, with dorsal surface of head and body dark to light brown or even reddish brown.

Ecology and habitat: Both the Perequê-Açú and the Taquari rivers are coastal basins with approximately 100 km2 of total area, flowing through a well-preserved area of Tropical Atlantic Forest. Along a longitudinal gradient, members of other loricariid species were collected up to 900 m above sea level, but H. nimius was collected only in localities between 100 and 370 m asl. All individuals were collected on rocky substrate with fast flowing, clear water, direct sunlight, and depths between 10 and 50 cm. Larger specimens were caught by moving rocks as large as possible in stronger water current. Underwater observations indicate that H. nimius is most active during the night, grazing on the bottom. During the day almost all individuals were seen under rocky boulders and stones, when these shelters were manually removed.

Other species collected together with H. nimius are: Kronichthys heylandi , Pareiorhina sp., Neoplecostomus sp., Schizolecis guntheri , Hisonotus notatus , Rhamdioglanis frenatus , Trichomycterus zonatus , Phalloceros sp., Bryconamericus microcephalus , Astyanax sp., Characidium japuhybensis , Rhamdia quelen , Pimellodela lateristriga , Acentronichthys leptos , Gymnotus pantherinus , Hollandichthys sp., Hyphessobrycon reticulatus , Synbranchus marmoratus , Centropomus parallelus , Geophagus brasiliensis , Eleotris pisonis , Gobionellus shufeldti and Awaous tajasica . The eleven first species were collected syntopically.

Distribution: Hemipsilichthys nimius is so far known only from its type-locality in the upper Perequê-Açu River and from the nearby Taquari River, in the southern coast of Rio de Janeiro State (Fig. 2).

Etymology: Specific epithet from the Latin nimius, meaning nimiety, excessive, in allusion to the supernumerary rays of the dorsal fin, which has seven to nine branched rays; all remaining species of the genus have seven. An adjective.

Discussion

In a recently published book, Reis et al. (2003) recorded 673 loricariid species currently recognized and estimated that an additional 300 species are yet to be described. The discovery of an undescribed Hemipsilichthys in the State of Rio de Janeiro, however, is quite surprising since that is one of the best sampled areas in South America.

The new species is easily distinguished from all other Hemipsilichthys species by modally having eight branched rays in the dorsal fin, by having the dorsal-fin membrane expanded posteriorly and connecting the proximal half of the last dorsal-fin ray to the dorsum, and by its symmetrical tooth cusps, which are asymmetrical in all other species except H. gobio and H. papillatus . It is further distinguished from these latter two species by the larger orbit diameter, and by the V-shaped dorsal-fin spinelet, but it shares with them certain features that might be indicative of close relationships. Pereira et al. (2000) discussed three putative synapomorphies shared by H. gobio and H. papillatus , which are also partially shared by H. nimius . 1) Anal fin of adult females much longer than that of males (Pereira et al. 2000, fig. 2); this was not verified in H. nimius and represents a synapomorphy of the two former species only. 2) Upper lip with papillae coalesced to form elongate, transverse skin-folds (Pereira et al. 2000, fig. 3); this is present in H. nimius but developed to lesser extent and not as elongate as in the former species. 3) More than one azygous preadipose plate forming a tall ridge with the anterior preadipose plates not contacting the dorsal-plate row. This is also present in H. nimius . Besides not being articulated with the preadipose plates, plates of the dorsal row on both sides do not contact each other behind the dorsal fin base in any of the three species. Finally, the tooth morphology, consisting of two fine and elongate symmetric cusps, shared by these three species might be an additional derived feature. This character, however, is shared with other basal loricariids like Delturus and Lithogenes , and also with some astroblepids.

As described in the Introduction, there is a gap in the distribution of Hemipsilichthys in coastal southeastern Brazil. Ten species occur in the coastal drainages and in the upper Uruguay River between Rio Grande do Sul and northern Santa Catarina States. North from that region, species of Hemipsilichthys are found from the coastal rivers of Rio de Janeiro State and Paraíba do Sul River to the north. The possible explanation to this distributional gap is based on two factors: 1) the rather large coastal drainage basin of the Ribeira de Iguape River, located in southern São Paulo State is inhabited by three species of the related genus Isbrueckerichthys , I. duseni (Miranda Ribeiro , 1907), I. alipionis (Gosline , 1947), and a third, new species being described by Edson H. L. Pereira and Osvaldo T. Oyakawa, which occupy the same niche as Hemipsilichthys species; and 2) in northern São Paulo State, between the Ribeira de Iguape and the Paraíba do Sul River basin, the Serra do Mar formation is very close to the ocean, leaving a narrow coastal plain with only very small rivers (see map in Pereira and Reis 2002, fig. 2).