An Omalonyx revisited

Arruda et al. (2016) recently published a revaluation of an Omalonyx species from Brazil. Species from this group are notoriously difficult to discern. “Omalonyx geayi Tillier, 1980 was originally described on the basis of specimens from Kaw swamp, French Guiana. This species distinguished from other of Omalonyx d’Orbigny, 1837: (i) by hermaphrodite duct twice as long and sacculate, without radial ducts but a funnel-shaped insertion on the ovariotestis, and (ii) by longitudinal wrinkled folds on the phallus inner wall. Two recent collections – from Trinidad and Carauari (Amazonas, Brazil) included specimens with ovariotestis and hermaphrodite duct morphologies similar to that originally described for O. geayi, but with phallus morphology not consistent with identification as O. geayi. A further eight lots, from Suriname, Ecuador, Brazil (Amazonas and Alagoas States), Bolivia and Cayenne-Kourou Road in French Guiana comprised specimens with phallus morphology analogous to O. geayi and ovariotestis and hermaphrodite duct similar to that of other Omalonyx species. Based on histological examination, and earlier phylogenetic analyses of morphological characters, we conclude that the ovariotestis and hermaphrodite duct conditions previously described for O. geayi were based on parasitized specimens. Accordingly, O. geayi is redescribed, and new information presented on the species’ wide distribution in South America”.

Schermafbeelding 2017-04-05 om 10.02.04

Based on histological and anatomical research, the authors conclude that the original description was based on parasitised specimens in which the ovariotestis and proximal hermaphrodite duct were deformed. O. geayi as currently understood is occurring more broadly in South America than previously thought. The study was based on specimens from Trinidad, Suriname, French Guiana, Ecuador, and Brazil.

Reference:
Arruda, J.O., Barker, G.M. & Thomé, J.W., 2016. Revaluation of the taxonomic characters and distribution of Omalonyx gaeyi (Gastropoda, Succineidae). – Iheringia, Zoologia, 106: e2016019 (6 pp.). DOI: 10.1590/1678-4766e2016019

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