Retroculus Eigenmann & Bray, 1894

Landim, Maria Isabel, Moreira, Cristiano R. & Figueiredo, Carlos A., 2015, Retroculus acherontos, a new species of cichlid fish (Teleostei) from the Rio Tocantins basin, Zootaxa 3973 (2), pp. 369-380 : 370

Retroculus Eigenmann & Bray, 1894

Diagnosis. Retroculus is distinguished from all other cichlid genera by the presence of two exclusive characters: epibranchial lobe supported by a thickening of the first epibranchial (vs. epibranchial lobe supported by the second epibranchial, or by a laminar expansion of the first epibranchial; Fig. 1 ); and the presence of a vomero-palatine apparatus on roof of the mouth (vs. roof of mouth not distinctively specialized; Fig. 2 ). Retroculus can also be distinguished by a combination of the following diagnostic characters: the presence of two lachrymal plates plus five tubular infraorbitals ( Fig. 3 ); a first tubular infraorbital only posteriorly associated with the orbit; the lip folds meeting without overlap at the corner of the mouth (African lips of Kullander, 1986; or type-I lip of Stiassny, 1987); presence of two supraneurals; the seven lateralis canal foramina in the preopercle; the five lateralis canal foramina on the dentary; a black blotch on the anterior soft dorsal-fin rays; the orobranchial mucosa laterally covered by papillae; by the presence of skin flaps and a lack of microbranchiospines along the external margin of the first ceratobranchial; attachment of the ligament hypohyal-hypobranchial 1 along the antero-medial spiny process of the first hypobranchial ( Fig. 4 ); supracleithrum laterosensory canal posteroventrally angled ( Fig. 5 ); posterior portion of the dentigerous arm of the dentary slender; and rakers at base of epibranchial lobe ( Fig. 6 B).

Figures

FIGURE 1. First epibranchial of (A) Retroculus acherontos, MZUSP 85838, (B) R. s eptentrionalis, MZUSP 38947, paratype, and (C) Satanoperca lilith, MZUSP 8503. Ventral view, anterior to top. Cartilage black. Scale bar = 1 mm.

FIGURE 2. Vomero-Palatine apparatus of (A) Retroculus acherontos, MZUSP 85826, 161.3 mm SL, (B) R. xinguensis, MZUSP 40682, 78.2 mm SL, and (C) R. septentrionalis, paratype, MZUSP 38947, 106.2 mm SL. Ventral view, anterior to top. Arrows indicate the lateral depressions. V indicate the ventral projection of vomer.

FIGURE 3. Lachrymals and tubular infraorbitals of Retroculus acherontos, MZUSP 85838. Lateral view, anterior to right. Scale bar = 3 mm.

FIGURE 4. First hypobranchial of (A) Retroculus acherontos, MZUSP 85838, and (B) R. septentrionalis, MZUSP 38947, paratype. Dorsal view, anterior to top. Cartilage black. Scale bar = 1 mm.

FIGURE 5. Supracleithrum of Retroculus acherontos, MZUSP 85838. Lateral view, anterior to left. Scale bar = 1 mm.

FIGURE 6. Epibranchial lobe on the first branchial arch of (A) Geophagus altifrons, MZUSP 8547, 148 mm SL, and (B) Retroculus acherontos, MZUSP 85826, 161.3 mm SL. Lateral view, anterior to left.