Abstract
Two new species of Hisonotus are described from the rio Paraná-Paraguay basin in Brazil. The most remarkable features of the new species are the odontodes forming longitudinally aligned rows (one odontode after the other, but not necessarily forming parallel series) on the head and trunk (vs. odontodes not forming longitudinally aligned rows), a pair of rostral plates at the tip of the snout (vs. a single rostral plate), the functional v-shaped spinelet (vs. spinelet non-functional, square-shaped, or absent). These features suggest close phylogenetic relationships with Hisonotus bockmanni, H. insperatus, H. luteofrenatus and H. piracanjuba. Additionally, both new species are distinguished from their congeners by characters related to head length and depth, orbital diameter, suborbital depth, caudal peduncle depth, pectoral-fin spine length, snout length and counts of teeth. Hisonotus paresi sp. n. further differs from its congeners by having contrasting dark geometric spots on the anterodorsal region of the body, a character lacking in H. oliveirai sp. n. The variation in number and shape of the rostral plate, posterior rostrum plates, infraorbitals and the preopercle in both new species and in H. insperatus are discussed.
Highlights
Hypoptopomatinae is composed of 19 genera and about 135 valid species (Eschmeyer and Fong 2013)
Additional characters used to distinguish Hisonotus from other genera of Hypoptopomatinae include a rostrum with enlarged odontodes and thickened plates forming the lateral rostral margins; the latter character is present in some other species of Hypoptopomatinae, especially in species of Microlepidogaster Eigenmann & Eigenmann, 1889 (Britski and Garavello 2007)
Hisonotus oliveirai is externally similar to H. insperatus and H. piracanjuba both species from upper stretches of the rio upper rio Paraná basin, H. paresi resembles more closely to H. bockmanni from the rio Tapajós basin
Summary
Hypoptopomatinae is composed of 19 genera and about 135 valid species (Eschmeyer and Fong 2013) This group includes Hisonotus Eigenmann & Eigenmann, 1889, which has as type species H. notatus Eigenmann & Eigenmann, 1889. Regan (1904) considered Hisonotus to be a synonym of Otocinclus Cope, 1871 This taxonomy had been followed until Schaefer (1998a), who resurrected Hisonotus and listed the following combination of diagnostic characters: reduced or absent snout plates anterior to the nostril, the rostrum with enlarged odontodes, and thickened plates forming the lateral rostral margin. Additional characters used to distinguish Hisonotus from other genera of Hypoptopomatinae include a rostrum with enlarged odontodes and thickened plates forming the lateral rostral margins; the latter character is present in some other species of Hypoptopomatinae, especially in species of Microlepidogaster Eigenmann & Eigenmann, 1889 (Britski and Garavello 2007). Based on recent collection efforts, we add two new species to the genus Hisonotus: one from the upper rio Paraná basin and the other as the first species for this genus from the rio Paraguay basin
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