Viriiella touaouroua Schröder, Schächinger, Bouchet & Haase, 2024, gen. et sp. nov.

Viriiella touaouroua gen. et sp. nov. urn:lsid:zoobank.org:act: 18A13BF1-D46C-4A61-A0F8-17B86351C903 Figs 3–8 Diagnosis Shell small, cylindrical to cylindro-conical, 1.8 to 2 times as high as wide, not more than four rather flat whorls; aperture semi-lunar, not extending far beyond the outline of the spire, lip continuous, slightly thickened, orthocline; umbilicus narrow; smooth protoconch with about 1.25 whorls. Etymology The epithetum refers to Touaourou, the name of the community of the type locality. Type material Holotype (Fig. 3A) NEW CALEDONIA • Province Sud, district of Yaté, community Touaourou, small stream draining a swamp below a slope dominated by Niauli trees on the western bank of the road; 22°11ʹ05.6ʺ S, 166°58ʹ15.0ʺ E; 3 Nov. 2016; Bouchet and Haase leg.; MNHN-IM-2000-39460. Paratypes (Figs 3B–D, 4) NEW CALEDONIA •> 50 specimens; same collection data as for holotype; MNHN-IM-2000-39461. Description SHELL (Figs 3–4; Table 2). Small (<1.3 mm high), cylindrical to cylindro-conical, 1.8 to 2 times higher than wide, not more than four rather flat whorls; aperture semi-lunar, not extending far beyond the outline of the spire, lip continuous, slightly thickened, palatal thinner, apical angle acute, orthocline; umbilicus narrow; smooth protoconch with 1–1.25 whorls. OPERCULUM (N=6). Ovate, thin, yellow, paucispiral, nucleus excentric, without smear or peg. EXTERNAL FEATURES (N=30). Epidermis without pigment; eyes black (Fig. 3), small; cephalic tentacles without ciliation. MANTLE CAVITY (N =2). Ctenidium with 10 filaments; osphradium ovate. DIGESTIVE SYSTEM. Radula formula R: 4–5 1 4–5 / 1 1, L: 3–4 1 6–7, M1: 17–19, M2: 14–15 (N= 1; Fig. 5); stomach with two equally sized chambers, proximal without caecum (N=5); pallial rectal loop in females wide adjoining the pallial oviduct, narrower in males, not adjoining the prostate (N=30). FEMALE GENITALIA (N =3; Fig. 6; Supp. file 1). Ovary a simple sack, starting at 1.5 whorls below the apex, comprising about ⅓ whorls, not reaching stomach; receptaculum seminis elongate, small with very short duct; bursa copulatrix large, elongate, club-shaped, reaching far behind albumen gland; anterior capsule gland much smaller than posterior one. MALE GENITALIA (N=5; Figs 7–8; Supp. file 2). Testis lobate, starting 0.75 whorls below apex, comprising up to 0.75 whorls, almost reaching stomach; vesicula seminalis below testis fairly small; vas deferens proceeding along stomach reaching kidney-shaped prostate ventrally, distal vas deferens leaving prostate at anterior tip, initially straight then undulating before reaching penis; penis simple, elongate, slender, simple, distal end blunt. Remarks Viriiella touaouroua gen. et sp.nov. is the smallest freshwater gastropod so far known from New Caledonia. Leiorhagium granum Haase & Bouchet, 1998, and L. granulum Haase & Bouchet, 1998, both only known by their shells, thus with tentative generic allocation, measure at least 1.5 mm in height and are much more conical (Haase & Bouchet 1998). The type locality lies in a narrow strip of alluvial deposits between the coast and a range of ultramafic hills (see https://georep.nc/explorateur-cartographique provided by the Gouvernement de la Nouvelle Calédonie). These slope colluviums come from the dismantling of the peridotite massif located directly to the West of the type locality and form an aquifer at the foot of the massif (probably temporary and perched), which is fed by both the drainage of the massif and also by the creeks of the area (L. Russ, pers. com.). Phylogenetic analyses Both ML and BA yielded almost identical topologies (Fig. 9). The ingroup, i.e., Tateidae, received full support. A clade containing Sulawesidrobia Ponder & Haase, 2005 and Tatea Tenison-Woods, 1879 was sister group to all remaining taxa, which formed two larger clades, both with two subclades. One clade contained all species of Fluviopupa and all species from New Zealand, while in the other one, Australian genera were sister to all species from New Caledonia. Within clades, there were only two differences: 1) in the relationships of the New Zealand genera Halopyrgus Haase, 2008, Potamopyrgus Stimpson, 1865, and Sororipyrgus Haase, 2008; 2) and most relevant for the present account, the relationship of the new genus Viriiella. In ML, V. touaouroua gen. et sp. nov. was sister species of Crosseana melanosoma (Haase & Bouchet 1998), in BA of Leiorhagium kavuneva Haase & Bouchet, 1998. Both relationships were only insignificantly supported. Some of the deeper nodes were not well supported, either.