Stenostomum tuberculosum Nuttycombe & Waters 1938

Stenostomum tuberculosum Nuttycombe & Waters, 1938 Fig. 4 A, B Sampling site. Display case with vegetation – Tank 1. Description. A Stenostomum, reaching a length of 600 μm in two-zooid individuals (Fig. 4 A). The head is triangular with a characteristic tubercle at the very top (Fig. 4 B). Sensory pits are directed anteriorly, deeply enclosed in the head. The pits are connected to the posterior brain lobes, which are oval (Fig. 4 B). The animals lack refracting bodies. The mouth opening is V-shaped and strongly muscular (Fig. 4 A). The pharynx is relatively short with fine granular gland cells, the refracting elements described by Marcus (1945) (Fig. 4 B). The posterior end of the gut does not extend to the caudal end, which is narrower than the rest of the body. The protonephridium is straight, with a terminal opening at the very end of the animal. The worms survived for only a few days in Chalkley’s Medium with wheat grain before the culture collapsed. We did not succeed in further attempts at culturing them. Distribution. US, Mountain Lake, Virginia, and pond at Athens, Georgia (Nuttycombe and Waters 1938); Brazil, streams in São Paulo (Marcus 1945); Poland, tanks in Poznań Palmhouse (Kolasa 1973); Surinam, Suriname River near Paramaribo (van der Land 1970); Germany and Finland (Lanfranchi and Papi 1978); Argentina, Buenos Aires (Noreña et al. 2005); Japan, Ikeura rice field (Yamazaki et al. 2012); Brazil, ESEC Taim water channel (Reyes et al. 2021).