Tuesday, August 7, 2012

[Ichthyology • 2008] Lithoxus jantjae • Description of a new Lithoxus (Siluriformes: Loricariidae) from the Guayana Highlands with a discussion of Guiana Shield biogeography

Lithoxus jantjae Lujan, 2008

Lithoxus jantjae, new species, is described from above Tencua Falls in headwaters of the Ventuari River, a white- to clearwater river flowing west from the Maigualida and Parima mountains in the Guayana Highlands of southern Venezuela. Lithoxus jantjae represents a nearly 600 km westward range expansion for a genus historically known only from Guyana, Suriname, French Guiana, and Brazil. Lithoxus jantjae shares with other species of Lithoxus a dorsoventrally depressed body and a large, papilose oral disk with small toothcups and few teeth. It can be distinguished from congeners by a unique combination of characters including 12 branched caudal-fin rays, medial premaxillary tooth cusps enlarged, and a convex posterior margin of the adipose-fin membrane. With the discovery of L. jantjae, Lithoxus becomes the most recent example of a growing list of rheophilic loricariid genera with disjunct distributions on east and west sides of the Guayana Highlands. A biogeographic hypothesis relying on the existence of a proto-Berbice River uniting the southern Guayana Highlands with rivers of the central Guiana Shield is advanced to partially explain the modern distribution of these species.

Key words: Ancistrini, Endemism, Faunal barrier, Proto-Berbice.

Distribution. Known only from rapids that extend for a few hundred meters upstream of Tencua Falls, the first major faunal barrier in the Ventuari River (pers. obs.), a right bank tributary of the upper Orinoco in Amazonas State, Venezuela (Fig. 2).

Etymology. Matronym honoring the author's mother, nicknamed Jantje prior to her emigration from the Netherlands, in deep appreciation for her hard work and material and emotional encouragement that promoted his professional development and made this research possible. Pronounced yäntchi.

Lujan, Nathan K. 2008. Description of a new Lithoxus (Siluriformes: Loricariidae) from the Guayana Highlands with a discussion of Guiana Shield biogeography. Neotropical Ichthyology. 6 (3): 413–418.