Tenellus, new genus

Fig. 71

Type species. Oxydoras trimaculatus Boulenger, 1898: 422, pl. 40 (fig. 1). Rio Jurua, an affluent of the Amazon, Brazil.

Included taxa. Tenellus trimaculatus (Boulenger, 1898), new combination (Fig. 71a); Tenellus ternetzi (Eigenmann, 1925), new combination (Fig. 71b); Tenellus leporhinus (Eigenmann, 1912), new combination (Fig. 71c).

Diagnosis. Tenellus is diagnosed by a single character state change: a distinct dark longitudinal stripe on middle of each lobe of the caudal fin (#1: 0>1, also present in Anadoras, Centrochir, Orinocodoras, Platydoras, and most Leptodoras). In addition, Tenellus is distinguished from other doradids by the following combination of characters: well-developed adipose eyelid (#2: state 1, vs. weakly developed in all doradids except Anduzedoras, Hassar, and some species of Leptodoras), large posterior cranial fontanel (#58: state 0, vs. reduced to a small opening in Nemadoras elongatus, N. humeralis, and Oxydoras, or completely occluded in all other doradids, except Anduzedoras, Hassar, Leptodoras, Nemadoras hemipeltis, and Trachydoras), sphenotic with lateral process (#62: state 1, vs. sphenotic without lateral process in all doradids except Anduzedoras, Doras, Hassar, and Leptodoras), posterior process of epiotic connected via ligament to posterior nuchal plate (#86: state 0, vs. connected via bony suture in Doras carinatus, D. micropoeus, D. higuchii, Hassar, Anduzedoras, and Leptodoras), infraorbital 1 with relatively small anterior portion (#100: state 0, vs. anterior portion relatively large in Doras carinatus, D. micropoeus, D. higuchii, Hassar, Anduzedoras, and Leptodoras), ceratohyal with large anterior process sutured to hypohyal (#174: state 2, vs. process small or absent in most doradids, except Hemidoras, Nemadoras, and Oxydoras), gill-rakers present on first two gill arches (#181: state 1, vs. absent in Trachydoras and some species of Leptodoras).

Etymology. Tenellus comes from the Latin tener, meaning delicate, in the diminutive form, tenellus, in reference to the delicate appearance of the species included in the new genus.

Remarks. Within Tenellus (Fig. 71), T. ternetzi and T. trimaculatus are considered sister taxa by sharing the loss of anterior nuchal plate (#228: 0>1). Tenellus leporhinus is readily distinguished from congeners by having midlateral scutes weakly developed on middle of body (#118: 2>1). Tenellus trimaculatus is distinguished from T. ternetzi by having well-developed bony lamina between internal process and basipterygium (#283: 1>0), and dark blotch on base of anteriormost dorsal-fin rays, including dorsal-fin spine but excluding spinelet (vs. dark blotch on spinelet but absent on dorsal-fin anteriormost rays).