Stichostemma asensoriatum, Montgomery, 1896

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 : 464

2. asensoriatum Montgomery, 1896

Source. In the binomen Stichostemma asensoriatum by Montgomery (1896: 436).

Type locality. A small stream, with the local name of Taylor’s Run, situated about a mile to the north-west of the town of W. Chester, Chester County, Pennsylvania, USA ( Fig. 9 ) .

Etymology. Adjective, asensoriatus, - a, - um; from the negative prefix a -, the Late Latin sensōriUm (“sensory apparatus”), and the adjective-forming suffix - ātUs, referring to the supposed absence of the frontal organ.

Remarks. The absence the frontal organ, alleged to be specific for S. asensoriatum , is unusual among monostiliferous hoplonemerteans. While a likely explanation for this absence is that it resulted from an artifact during paraffin sectioning, this hypothesis is hardly falsifiable (but see Fig. 3C, D ). Prostoma asensoriatum is listed as a valid name by some authors (e.g., Bürger 1904: 69; Gibson 1995: 493; Chernyshev et al. 1998: 61; Sundberg & Gibson 2008: 62), although it was regarded as invalid by Stiasny-Wijnhoff (1938: 226) and Gibson & Moore (1976: 212). Stichostemma asensoriatum is herein considered synonymous with P. clepsinoides .

Figures

FIGURE 3. Prostoma clepsinoides Dugès, 1826 from Lake Biwa, Japan.A, Obliquely sagittal section through the rhynchodaeal opening; anterior to the left. B, Horizontal section showing well-developed frontal organ, indicated by arrowhead; anterior upward. C, D, Two serial horizontal sections showing poorly developed frontal organ (indicated by arrowheads) that could otherwise be overlooked or interpreted as absent; anterior upward. A, ICHUM 6278; B, ICHUM 6275; C, D, ICHUM 6274.

FIGURE 9. World map showing distribution of 25 nominal species of freshwater monostiliferous hoplonemerteans indicated by boxes and respective species-group names (three subterranean species are indicated with ‘S’ in parentheses); circles, diamond, and triangles indicate localities of DNA-barcoded individuals; circles, Haplogroup 1 from the UK, Sweden (SE), Italy (IT), Macedonia (MK), Japan (JP), New Zealand (NZ), Mexico (MX), Indiana (IN), and Massachusetts (MA); diamond, Haplogroup 2 from Norway (NO); triangles, Haplogroup 3 from Sweden (SE) and California (CA).