Retroculus acherontos, a new species of cichlid fish (Teleostei) from the Rio Tocantins basin Author Landim, Maria Isabel Author Moreira, Cristiano R. Author Figueiredo, Carlos A. text Zootaxa 2015 3973 2 369 380 journal article 10.11646/zootaxa.3973.2.10 0b0db3fd-d54b-432b-a661-408f1ac32abc 1175-5326 245230 4E6E002C-309C-47EB-964C-BF5A06FEC62E 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).