Alvania Risso, 1826

Amati, Bruno, Giulio, Andrea Di & Oliverio, Marco, 2023, Shallow-water Rissoidae of the genera Alvania Risso 1826 Haurakia Iredale 1915 Parashiela Laseron 1956 Simulamerelina Ponder 1985 and Subestea Cotton 1944 Gastropoda Caenogastropoda Rissooidea from French Polynesia with the description of a new deep-water genus, Zoosystema 45 (25), pp. 803-892 : 806

Genus Alvania Risso, 1826

Alvania Risso, 1826: 140 .

TYPE SPECIES. — Alvania europea Risso, 1826: 142 , pl. IX, fig. 116. Synonym of Alvania cimex (Linnaeus, 1758) by subsequent designation ( Nevill 1885: 105).

DIAGNOSIS. — Shell from scarcely to very robust, from small to large for the family (1-7 mm hight), ovate-conical, generally with axial and spiral elements forming a clathrate sculpture. Aperture piriform, peristome continuous and simple; outer lip with moderate to very robust varix, inner side smooth or with teeth. Umbilical fissure generally absent. Protoconch multispiral or paucispiral, smooth to heavily sculptured.

Head-foot: cephalic tentacles long, ciliated, with parallel sides; anterior and posterior pallial tentacles present in most species; metapodial tentacles, in most species, 3-7; anterior pedal gland present, posterior pedal gland usually inconspicuous and possibly absent in a few species. Operculum: thin, nucleus eccentric, paucispiral (after Ponder 1985: 36).

REMARKS

The genus Alvania Risso, 1826 as currently conceived includes a speciose group of small to large sized rissoid species living from the lower intertidal to bathyal depths, mostly on the continental shelf, where they are prevalently associated with algal facies (e.g. Ponder 1985: 2; Gofas 2007: 779; Ávila et al. 2012), with few representatives in deeper waters down to 4700 m depth ( Bouchet & Warén 1993). They feed on diatoms, dinoflagellates, and detritus, with the deep-sea species presumably selective deposit feeders ( Ponder 1985). The genus is based on the Mediterranean Alvania europea Risso, 1826 , and includes a remarkable radiation in the northeastern Atlantic and the Mediterranean Sea; the inclusion of species from other biogeographic provinces may (or may not) make it polyphyletic (see e.g. Criscione et al. 2016) and its actual taxonomic extension needs to be tested by integrated molecular and anatomical studies. As currently conceived (for the long list of synonyms, not reported here, see MolluscaBase 2023b), Alvania comprises species from a wide geographic range, spanning the northeastern Atlantic and Mediterranean, the northwestern Atlantic and the Caribbean, the eastern Pacific, the Indo-West Pacific, temperate Australia, and South Africa ( Ponder 1985), and includes 265 known Recent species and 177 fossil ones ( MolluscaBase 2023b). The genus dates back to the European Oligocene ( Cossmann & Pissarro 1913; Lozouet 1998; Garilli & Parrinello 2010), with the extant fauna being the result of the large diversification from the Miocene to the Pleistocene (e.g. Sacco 1895; L. Seguenza 1903).

Several taxa originally introduced under other genera, actually belong to Alvania as currently conceived. For instance, the examination of the type material of Rissoa denseclathrata Thiele, 1925 (10 syntypes ZMB/Ma.64984: Fig. 2 A-G), from Cape Agulhas, South Africa, in 80 m ( Thiele 1925: 81, pl. 6, fig. 11) and of Rissoa proditoris Thiele, 1925 (10 syntypes, ZMB/Moll.64965: Fig. 3 A-G) from Angola and Agulhas Bank, South Africa ( Thiele 1925: 46, pl. 6, fig. 9) are very similar to e.g. Alvania herosae n. sp., and we accordingly propose Alvania denseclathrata ( Thiele, 1925) n. comb. as a new combination for Rissoa denseclathrata Thiele, 1925 and Alvania proditoris ( Thiele, 1925) n. comb. as a new combination for Rissoa proditoris Thiele, 1925 (for details see below).

Rissoa (Alvania) lusoria Yokoyama, 1926 , from the Pliocene of Sado Island ( Japan: Yokoyama 1926: 273, pl. 33, fig. 18; Makiyama 1958, pl. 45, fig. 18; Hasegawa 2014: 123, fig. 34) is also very similar to Alvania herosae n. sp., and we accordingly propose Alvania lusoria ( Yokoyama, 1926) as a new combination for Rissoa (Alvania) lusoria Yokoyama, 1926 (see below for details).

The examination of c. 5250 specimens from French Polynesia, allowed us to identify five shallow water species, all undescribed: Alvania letourneuxi n. sp., Alvania herosae n. sp., Alvania parvimaculata n. sp., Alvania prosocostata n. sp. and Alvania uapou n. sp.

Figures

FIG. 2. — Alvania denseclathrata (Thiele,1925) n. comb.:A-E, Lectotype,height 2.2 mm,width 1.35 mm,South Africa,Valdivia Stn 95, 80 m, ZMB/Moll.N ° 64984: shell (A-C); detail of the first whorls (D, E); F, original labels; G, original drawing. Scale bars: D, E, 20 μm.

FIG. 3. — Alvania proditoris (Thiele, 1925) n. comb.: A-E, lectotype, height 2.75 mm, width 1.65 mm, South Africa, Valdivia Stn 101, depth unknown, ZMB/Moll. N° 64965: shell (A-C); detail of the first whorls (D, E); F, original labels; G, original drawing. Scale bars: D, E, 20 μm.