Stenostomum hemisphericum Nassonov, 1924

João A. L. Braccini, Francisco Brusa & Ana M. Leal-Zanchet, 2017, Six freshwater microturbellarian species (Platyhelminthes) in permanent wetlands of the Coastal Plain of southern Brazil: new records, abundance, and distribution, Check List 13 (6), pp. 849-855 : 852-853

Stenostomum hemisphericum Nassonov, 1924

Figures 8, 9

General morphology. Specimen with 2 zooids, reaching a length of 5 mm ( Figs 8, 9 ). Similar to the specimens analyzed by Marcus (1945a), the brain is divided into 2 portions, the anterior lobes are separated in small independent parts and the posterior lobes are trilobated with 2 light-refracting bodies, constituted by a pear-shaped vesicle (0.01 mm in diameter) and a spherical refractory element in its inner part associated with the posterior lobe. The mouth is rounded. The simplex pharynx is long, consisting of strong muscles, with longitudinal, circular, oblique and lateral muscle fibers. The nephridiopore is subterminal ( Fig. 9 ). The pharyngeal glands showed a restricted distribution around the mouth and the posterior portion of the brain was relatively smaller than that of the specimens from the type locality, in the Holarctic region ( Nassonov 1924).

Specimens examined. Coll. J.A.L. Braccini and F. Brusa, 12 March 2012, Brazil, Rio Grande do Sul, Terra de Areia (29°29ʹ 0 5 ʺ S, 0 49 °52ʹ21ʺ W). No voucher available.

Remarks on ecology and distribution. This species was represented by a singleton in the summer/autumn survey and was absent in the winter/spring survey ( Table 2 ). It was described from the Holarctic region ( Nassonov 1924); in the Neotropical region, it was reported at Belém, northern Brazil ( Marcus 1945a) and in the department of Ucayali, Peru ( Damborenea et al. 2011). The present record increases its known distribution by about 3000 km to the southeast.

Order Dalytyphloplanida Willems, Wallberg, Jondelius, Littlewood, Backeljau, Schockaert & Artois, 2006 Family Provorticidae Beklemischev, 1927 Genus Baicalellia Nassonov, 1930

Figures

Figures8, 9. Photographof specimen invivoafter squeeze preparation (8) and diagrammatic reconstruction (9) in dorsal view of Stenostomum hemisphericum recorded for the Coastal Plain of southernBrazil.