Tetrastemma aquarumdulcium, Silliman, 1884

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

1. aquarumdulcium Silliman, 1884

Source. As “ Tetrastemma aquarum dulcium ” [sic] by Silliman (1884: 70, pl. III, figs 19–24).

Type locality. Monroe County, New York State, USA ( Fig. 9 ) .

Etymology. Latin feminine noun in the genitive plural, meaning “of sweet waters”.

Remarks. The monostiliferous hoplonemertean proboscis and the characteristic six eyes depicted in the original illustration of the entire body ( Silliman 1884, pl. III, fig. 19), along with its occurrence in a freshwater environment, undoubtedly indicate that the nominal species Tetrastemma aquarumdulcium belongs to Prostoma . Other than “ Tetrastemma aquarum dulcium ”, Silliman (1884) described and re-described 15 species of freshwater turbellarians. Because these 15 were all indicated by binomina, Silliman’s (1884) article can be regarded as consistent with the Principle of Binominal Nomenclature (cf. Article 11.4). It is clear from the description of this taxon placed in Tetrastemma that Silliman (1884) had no intention to establish a new subspecies; besides, there had been no such species as “ Tetrastemma aquarum ”. The two words “ aquarum dulcium ” together refer to “of sweet waters [of freshwater]” and thus can be deemed “a single entity” in the sense of Article 11.9.5. Therefore, these should be united as aquarumdulcium , rather than the hyphenated form aquarum-dulcium employed by Monticelli (1916: 415) and Corrêa (1964: 549). Volume 41 of Zeitschrift für wissenschaftliche Zoologie contains four issues: the first issue was published on 4 November 1884, the second on 30 December 1884, the third on 17 March 1885, and the fourth on 8 May 1885. Silliman’s article was included in the first issue; thus, the date of publication for Tetrastemma aquarumdulcium is 1884, instead of 1885, as mentioned by later authors (e.g., Bürger 1895: 590; Gibson 1995: 511). Tetrastemma aquarumdulcium has been regarded as synonymous with Prostoma clepsinoides by Bürger (1904: 68) and with Prostoma graecense by Stiasny-Wijnhoff (1938: 226). Gibson & Moore (1976: 197) considered Prostoma aquarumdulcium as a nomen dubium, stating that “[s]ince the form cannot be clearly distinguished from most of the remaining Prostoma species, the name aquarum dulcium must be invalidated”. Tetrastemma aquarumdulcium is now once again placed in the synonymy of P. clepsinoides .

Figures

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).