Prostoma ohmiense, Chernyshev et al., 1998

Kajihara, Hiroshi, 2025, A taxonomic revision of the freshwater monostiliferous hoplonemertean genus Prostoma Dugès, 1828 (Nemertea: Eumonostilifera): a radical solution or an over-lumping?, Zootaxa 5646 (4), pp. 451-500 : 470

18. ohmiense Chernyshev et al., 1998

Source. In the binomen Prostoma ohmiense by Chernyshev et al. (1998: 53).

Type locality. Off Shin-asahi-chō, Lake Biwa, Shiga Prefecture, Japan (Figs 1, 9) .

Etymology. Adjective, ohmiensis, - is, - e, meaning “from Ohmi”; Ohmi is an old Japanese place name referring to the district around Lake Biwa.

Remarks. Prostoma ohmiense was listed as a valid taxon by Sundberg & Gibson (2008: 62). It was described based on specimens from Lake Biwa and was reportedly differentiated from other congeners by the following characteristics: i) four or six pairs of eyes, ii) a rhynchodaeal wall with thin longitudinal muscles, iii) a proboscis with nine nerves, iv) oesophageal epithelium largely devoid of cilia, with sparse cilia present ventrally, v) an indistinct pylorus, and vi) cephalic glands extending back to the brain and opening externally via the frontal organ. However, each individual character state was found in at least one of the nine specimens examined in this study. For example, character i) was observed in ICHUM 6278; ii), vi), v), vi) were observed in ICHUM 6272; and iii) was observed in ICHUM 6277. This pattern can be interpreted as evidence that these traditionally used morphological characters vary either intraspecifically or randomly during histological preparation (e.g., protrusion of the oesophagus or stomach during fixation), rendering them unreliable for species-level discrimination. Indeed, previous studies have reported that differences in such internal characters may either be masked by contraction artifacts during fixation or fall within the range of intraspecific variation in some marine monostiliferans ( Sundberg 1979, 1980; Norenburg 1986; Envall & Sundberg 1993). The present material from the type locality now suggests that this nominal species belongs to the cosmopolitan epigean Prostoma , to which the name P. clepsinoides is applied in this paper.