Redescription of the Guiana Shield Darter Species Characidium crandellii and C. declivirostre (Crenuchidae) with Descriptions of Two New Species
Based on collections made in the western Guiana Shield over the last 21 years, Characidium crandellii and C. declivirostre are redescribed and two similar species are described from Guyana. These species all have enlarged paired fins with three to four rays thickened ventrally on the pectoral fin and two rays thickened on the pelvic fin. The species can be separated from all other Characidium and Melanocharacidium by having the venter unscaled from the isthmus to the pelvic origin. Characidium crandellii is found in the Essequibo and Takutu River systems and in an isolated population above Tencua Falls in the Ventuari River and the upper Paragua River (Orinoco River basin). Characidium declivirostre is found throughout the right-bank, shield tributaries of the Orinoco River system and in the upper Negro River. Characidium duplicatum, new species, appears to be rare but widely distributed in the Essequibo River system. Characidium wangyapoik, new species, is only known from the upper Ireng River, Branco River basin, along the border between Brazil and Guyana.
Thickened, keratinized pads on the undersurface of the anterior pectoral-fin rays of (A) Characidium wangyapoik, new species, CSBD F-3615, holotype, and (B) C. crandellii, AUM 67142. Photos by N. K. Lujan.
(A) Landmarks used in geometric morphometrics. Specimens were propped to maintain bodies orthogonal to the lens (Characidium declivirostre, AUM 36674, 44.0 mm SL); photo by J. W. Armbruster. (B) Wireframes of changes along PC1; gray is average shape and black is a shape that corresponds to a shape with +0.1 Procrustes units. (C) Wireframes of changes along PC2 colored as in B. (D) Results of PCA of geometric morphometrics; specimens of C. crandellii are split by basin with a syntype (Amazon basin) indicated in black.
Plot of the ratio of orbital diameter to head length versus standard length for all measured specimens of fast-water Characidium of the Guiana Shield showing allometry in eye size.
Dorsal, lateral, and ventral views of Characidium crandellii in life, potential nuptial male, AUM 67142, 106.9 mm SL; Ireng River population. Photos by N. K. Lujan.
Dorsal and lateral views of Characidium crandellii in life, common coloration, AUM 62874, 57.0 mm SL; Kuribrong River population. Photos by J. W. Armbruster.
Distribution of Characidium crandellii, type locality indicated with T.
Dorsal, lateral, and ventral views of Characidium declivirostre in life, AUM 56680, 55.5 mm SL; Raudales Danto, Río Cuao, Amazonas, Venezuela. Photos by N. K. Lujan.
Dorsal, lateral, and ventral views of a specimen of Characidium declivirostre from the same stream as the type locality, AUM 36625, 50.1 mm SL. Scale = 1 cm. Photos by J. W. Armbruster.
Distributions of Characidium declivirostre, C. duplicatum, new species, and C. wangyapoik, new species. Type localities indicated by T's (approximated for C. declivirostre).
Lateral view (top) of Characidium duplicatum, new species, in life and dorsal, lateral, and ventral views after preservation, CSBD F-3614, holotype, 39.4 mm SL. Photos by J. W. Armbruster.
Dorsal, lateral, and ventral views of Characidium wangyapoik, new species, in life, CSBD F-3615, holotype, 72.6 mm SL. Photos by N. K. Lujan.
Dorsal, lateral, and ventral views of Characidium wangyapoik, new species, after preservation, CSBD F-3615, holotype, 72.6 mm SL; Kuribrong River population. Photos by J. W. Armbruster.
Contributor Notes
Associate Editor: R. E. Reis.