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| Hypomasticus rectangulatus Ito, Gama, Sabaj & Birindelli, 2026 |
Abstract
A new species of Hypomasticus is described from the Vila Nova River, a left-bank tributary to the lower Amazon in the state of Amapá, Brazil. The new taxon belongs to the Hypomasticus granti group, a clade recently corroborated by molecular phylogenetics, and is diagnosed by a color pattern distinctive among anostomids: midlateral side with dusky rectangular blotch extending from the opercle to near vertical through dorsal-fin origin and followed by three dark oblong (vertically elongated) blotches well separated on posterior half of body, and (in adults) scales in anterior portion of lateral line and flanking rows with a dark spot at their base, forming three longitudinal rows within the dusky rectangular blotch. It further differs from congeners by having 32–34 perforated lateral-line scales and 12 circumpeduncular scale rows. Osteological examination revealed polymorphism in the number of dentary teeth regarding the presence of a fifth tooth, a condition previously observed in other members of the H. granti group. Sexual dimorphism was recorded with males exhibiting hypertrophy of the first pair of ribs, a condition previously unknown within this clade.
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| Hypomasticus rectangulatus. (A) IEPA 5637, holotype, 213.3 mm SL and (B) IEPA 5417, paratype, 89.84 mm SL. Brazil, Amapa´ state, municipality of Mazaga˜o, rio Vila Nova. Photos by M. Sabaj. Scale = 1 cm. |
Hypomasticus rectangulatus sp. nov.
Etymology.—The specific epithet rectangulatus is derived from the Latin word meaning rectangular or right-angled, in reference to the distinctive rectangular blotch present on the anterior midlateral region of the body. An adjective.
Ian Solon Bortoloci Ito, Cecile de Souza Gama, Mark Henry Sabaj and José Luís Olivan Birindelli. 2026. A New Species of Hypomasticus (Characiformes: Anostomidae) from the Vila Nova River, State of Amapá, Brazil. Ichthyology & Herpetology. 114(3); 507-519. DOI: doi.org/10.1643/i2025102 (22 September 2026)
