Pusillina sp.
Creators: name: Amati, Bruno
name: Taviani, Marco
name: Oliverio, Marco
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Rissoidae
Pusillina
Pusillina sp.

description: Pusillina sp.
(Fig. 8H; 9P)
Rissoa sulzeriana — Cavallo & Repetto, 1992: 50, fig. 071 (not Risso, 1826)
Pusillina (Pusillina) sulzeriana — Bernasconi & Robba, 1994: 73, 95, pl. 1, figs 1–5 (not Risso, 1826)
Pusillina sulzeriana — Chirli, 2006: 49, pl. 22, figs 8–12 (not Risso, 1826)
Pusillina sulzeriana — Tabanelli et al. 2011: 55, 67, pl. 8, figs 46–48 (not Risso, 1826)
Pusillina sulzeriana — Bellagamba et al. 2018: 78, pl. 1M, N (not Risso, 1826)
Pusillina sulzeriana — Tabanelli et al. 2020: 36, 37, pl. 1, fig. 13 (not Risso, 1826)
Other iconographic references. Chirli & Linse 2011: 72, pl. 18, figs 6a–c; Chirli & Forli 2021: 290, 291, pls 44, 45, figs B1–15, A1–10).
Material examined. An intact adult specimen was found in stn COR 2-53 (see Table 1; Figs 8H; 9P).
Distribution. Pliocene: Italy (Piedmont) (Cavallo & Repetto 1992: 50), Liguria (Bernasconi & Robba 1994: 73), Emilia-Romagna (Tabanelli et al. 2011: 55; Bellagamba et al. 2018: 78; Tabanelli et al. 2020: 35). Pleistocene: Tuscany (Chirli 2006: 49). The shell from stn COR 2-53 is likely a Plio-Pleistocene sample.
Remarks. The specimen studied is very similar to the specimens reported in recent literature under the name Pusillina sulzeriana (Risso, 1826) (see above, Other iconographic references). Alvania sulzeriana Risso, 1826 is considered as a taxon inquirendum (MolluscaBase, 2023). The lectotype of Alvania sulzeriana (Risso, 1826: 145, pl. IX, fig. 124; MNHN-IM-2000-35924; Figs 8A, B), a subfossil from the southern French coasts (http://coldb.mnhn. fr/catalognumber/mnhn/im/2000-35924), is definitely a specimen of the genus Rissoa, identifiable with Rissoa variabilis (Von Mühlfeldt, 1824) especially in its form brevis (Monterosato in BDD, 1884: 265, pl. XXXI, figs 6–10 = Rissoia neglecta Locard, 1886: 256) (Fig 8E), based on the large size (lectotype, height 5 mm; paralectotype, 6 mm), robustness of the shell, low height/width ratio, presence of axial ribs with abapical thickening, and dense spiral striae on the whorls (see for comparison also the specimen of Rissoa variabilis var. brevis Monterosato, MCZR-M-22024/22032, from Saint Raphael, Côtes de Provence, France: Figs 8F, G).
After the original description of Alvania sulzeriana Risso, 1826, subsequent authors used this name, essentially due to the ambiguous description and the hardly interpretable original drawing, for their specimens of Alvania Risso, 1826, Rissoa Desmarest, 1814, Apicularia Monterosato, 1884 and Pusillina Monterosato, 1884. It is known (Arnaud 1978: 101) that the Risso collection, was not accessible to his contemporary scholars; furthermore, to worsen the situation, P. Gény painted, in the 1840s, the types of Risso, including Alvania sulzeriana, showing with a lot of imagination, the presence of marked denticles on the inner side of the outer lip (Arnaud 1978: 141, pl. 8, fig 62), a typical character of species of Alvania.
Schwartz (1864: 40, pl. 3, figs 30, two figures, as Rissoa sulzeriana, from sub-Apennine formations of Modena and Siena, Italy) and Malatesta (1974: 176, 51, pl. 13, fig. 18, as Apicularia sulzeriana from the Pliocene of Ficulle, Umbria, Italy), figured specimens rather close to those species of Rissoa once included in the Apicularia group. For an overview of the literature citing the nominal taxon Alvania sulzeriana, see Chirli (2006: 49), who, however, figured and described a species different from both A. sulzeriana Risso, 1826 and our Pusillina sp.
Bernasconi & Robba (1994: 73, pl. 1, figs 1–5), described as Pusillina (Pusillina) sulzeriana (Risso, 1826), some specimens correctly ascribed to the genus Pusillina, but probably belonging to more than one species. The specimens figured in their figs 1–3, are probably referable to the same entity as our specimen of Pusillina sp. from Stn COR 2-53.
Our Pusillina sp. (Figs 8H, 9P) differs from Rissoa sulzeriana (Risso, 1826) [= Rissoa variabilis (Von Mühlfeldt, 1824) new synonymy] in its smaller size and weaker shell (height 1.9 mm vs height 5–6 mm in R. sulzeriana); in the lack of labial thickening, less convex whorls with no angularity, narrower axial ribs without abapical swelling, sparser spiral sculpture present only on the abapical part of the whorls.
Pusillina sp. differs from Pusillina inconspicua (Alder, 1844) mainly in its more obtuse apical whorls, wider umbilical fissure, and orthocline vs slightly opisthocline and flexuous axial ribs in P. inconspicua. Based on the figure by Tabanelli et al. (2011: 67, pl. 8, fig. 46b) the protoconch of P. sulzeriana is sculptured by a suprasutural threadlet, more evident on the last whorl; the protoconch-teleoconch boundary is marked by a sinusigera notch. The colour pattern is also different: monochrome in Pusillina sp. vs yellowish-white with subsutural and basal spots, nucleus of the protoconch always violet in P. inconspicua.
Pusillina sp. differs from Alvania varia Tabanelli, Bongiardino & Perugia, 2011, in its form attenuata (from the Pliocene of Romagna) (Tabanelli et al. 2011: 47, 65, pl. 6, figs 31–34) in the different protoconch: multispiral in Pusillina sp., paucispiral in A. varia.
Pusillina sp. is certainly a shallow water species; the shell from Stn COR 2-53 is thus quite probably a fossil, of either Pliocene or Pleistocene age.
description: Published as part of Amati, Bruno, Taviani, Marco & Oliverio, Marco, 2024, Rissoidae (Mollusca, Gastropoda, Rissooidea) from taphocoenotic assemblages of the Strait of Sicily (Mediterranean Sea) with the description of two new species, pp. 19-37 in Zootaxa 5432 (1) on pages 29-33, DOI: 10.11646/zootaxa.5432.1.2, http://zenodo.org/record/10898484