Revision of Oxyropsis Eigenmann and Eigenmann, 1889(Siluriformes, Loricariidae)

The armored catfish genus Oxyropsis is diagnosed as a monophyletic assemblage of three species of the family Loricariidae on the basis of presence of a single row of enlarged odontodes along the trunk midline lying adjacent, and immediately dorsal to, the lateral line canal. Oxyropsis is here resurrected from synonymy with Hypoptopoma Günther (1868) and three species, distributed in the middle and upper Amazon, Negro, and Orinoco basins of South America, are diagnosed and redescribed. The type species, Oxyropsis wrightiana Eigenmann and Eigenmann (1889), occurs in the upper Amazon and lower Ucayali River basins and is diagnosed among congeners by the presence of seven ultimate median series trunk plates, which are progressively smaller and narrower than the immediately preceding plates, and by pectoral spine serrae either extremely reduced in size (height less than one-sixth of the spine width) or absent. Oxyropsis carinata (Steindachner, 1879) occurs in the middle and upper Amazon River basin and is diagnosed by the presence of three or four ultimate plates of the median series distinctly narrower than preceding plates, pectoral spine serrae well developed both in size (tooth height approximately one-fifth of the spine width) and extent along the spine shaft and by greater numbers of teeth. Oxyropsis acutirostra Ribeiro (1951) occurs in the Negro and upper Orinoco basins and is diagnosed by the presence of a truncated median plate series, plates not extending to the caudal fin base and fewer teeth. Its holotype is presumed lost. Among Oxyropsis species, caudal peduncle depression covaries with standard length and degree of median plate series reduction. This observation, coupled with intrinsic differences in the association of related features among loricariids, further supports the hypothesis that trunk depression and caudal peduncle elongation have coevolved multiple times within the Loricariidae.

Fig. 1.

Left lateral view of the trunk plates of Oxyropsis species. (A) Oxyropsis wrightiana, (B) Oxyropsis carinata, (C) Oxyropsis acutirostra. Scale is 5 mm

Fig. 2.

Left lateral view of the posterior caudal peduncle of (A) Oxyropsis wrightiana, (B) Oxyropsis carinata, (C) Oxyropsis acutirostra, (D) Loricaria cataphracta. Scale is 1 mm

Fig. 3.

Pectoral fin spine, right side, anterior toward bottom. (A) Oxyropsis wrightiana, (B) Oxyropsis carinata, (C) Oxyropsis acutirostra. Scale is 1 mm

Fig. 4.

Oxyropsis wrightiana, holotype, MCZ 8055, 37.3 mm SL female, Brazil: Lago Janauari.

Fig. 5.

Drainage map of northern South America showing distribution of Oxyropsis species. Symbols may indicate more than one collection locality; open symbols designate holotype locality

Fig. 6.

Oxyropsis carinata, holotype, NMW 46267, 47 mm SL, juvenile, Perú, side streams of the Río Amazonas along the Peruvian border

Fig. 7.

Oxyropsis acutirostra, MCZ 59695, 34.5 mm SL female, Brazil, Amazonas, small stream flowing from east into Rio Guieiras, about 3 km from its confluence with Rio Negro