Avalithoxus, Lujan & Armbruster & Lovejoy, 2018

AVALITHOXUS GEN. NOV.

urn:lsid:zoobank.org:act:68E963BF-A8CA-437C-BE9C-DD593968E34D

Type species: Lithoxus jantjae Lujan, 2008: 414 .

Diagnosis: Avalithoxus can be diagnosed from other members of Lithoxini by having 12 branched caudal-fin rays (vs. 14 or, rarely, 13), four branched anal-fin rays (vs. five in Paralithoxus ), five interdorsal plates (vs. six to nine in Exastilithoxus and Paralithoxus ), at most low hemispherical papillae around the oral disc margin ( Fig. 1; vs. digitate papillae in Exastilithoxus ), and a maximum of 25 hypertrophied cheek odontodes (mode, 18; range, 16–25) vs. a maximum of 21 in Lithoxus (mode, 12; range, 5–21).

Etymology: Avalithoxus is a portmanteau of the Latin word ava, meaning ‘grandmother’, and the genus name Lithoxus . It refers to both the apparently basal position of this lineage and the matronym of the type species, which honoured Jeanne Lujan, mother of N.K.L.

Composition: Avalithoxus currently includes only Avalithoxus jantjae (Lujan, 2007) .

Geographical range: Avalithoxus is known only from ~ 180 m a.s.l. in the Ventuari River, immediately upstream of Salto Tencua in the central region of Amazonas State, Venezuela ( Fig. 2). Repeated sampling of habitats immediately downstream of Salto Tencua, at ~ 130 m a.s.l., in 2004 and 2010, and ~50 linear km further upstream (130 m higher elevation) in 2010, yielded no specimens of Avalithoxus . At our most upstream sampling points in the Ventuari River, near the Yekuana community of Cacuri, Avalithoxus was entirely replaced by an undescribed species of Exastilithoxus that we found in the present study to be sister to E. fimbriatus . Across the ~50 linear km between Salto Tencua and Cacuri, there is a 130 m drop in river elevation and a long series of high-energy rapids that might act as a barrier or intergrade zone between these two Lithoxini lineages.

Interlandmarks are the points between which each measurement was made (from Armbruster, 2003). Abbreviations: D, depth; HL, head length; L, length; N, number of specimens examined; SL, standard length; W, width.