Rissoina pusilla
Creators: name: Sacchetti, Claudia
name: Landau, Bernard
name: Ávila, Sérgio P.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Rissoinidae
Rissoina
Rissoina pusilla

description: Rissoina pusilla (Brocchi, 1814)
Plate 3 D 1 -D 3
* Turbo pusillus Brocchi 1814: 381, pl. 6, fig. 5.
Rissoina sp. Bronn in Reiss 1862: 32.
? Rissoina Bronni Mayer 1864: 57, pl. 6, fig. 37.
Rissoina pusilla Broc. — Mayer 1864: 57.
Rissoina pusilla (Br.) — Sacco 1895b: 35, pl. 1, figs. 98-101.
Rissoina (Rissoina) pusilla (Brocchi) 1814 —Rossi Ronchetti 1955: 101, fig. 45.
Rissoina (Rissoina) bruguierei (Payraudeau, 1826) — Cavallo & Repetto 1992: 54, fig. 084 (non Payraudeau, 1826).
Rissoina pusilla (Brocchi, 1814) — Chirli 2006: 53, pl. 23, figs. 13-15, pl. 24, figs. 1-5.
Rissoina pusilla (Brocchi, 1814) — Zunino & Pavia 2009: 51, pl. 1, fig. 3.
Rissoina pusilla (Brocchi, 1814) — Sosso & Dell’Angelo 2010: 22: 32, unnumbered fig. bottom right.
Rissoina pusilla (Brocchi, 1814) — Tabanelli et al. 2011: 30, fig. 51.
Rissoina pusilla (Brocchi, 1814) — Brunetti & Vecchi 2014: 75, pl. 5, fig. c.
Rissoina pusilla (Brocchi, 1814) — Brunetti & Cresti 2018: 48, fig. 114.
Rissoina pusilla (Brocchi, 1814) — Tabanelli et al. 2020: 30, pl. 3, fig. 38.
non Rissoina pusilla Brocc. —Ĥrnes 1856: 557, pl. 48, fig. 4 (= Rissoina podolica Cossmann, 1921).
non Rissoina pusilla Brocc. —Friedberg 1914: 358, pl. 20, fig. 22 (= Rissoina podolica Cossmann, 1921).
Santa Maria material examined. Maximum height 6.5 mm, width 2.3 mm. DBUA-F 488-1 (2), DBUA-F 827-G (17), Ponta do Castelo; DBUA-F 1295-I (2), Malbusca (east cave); DBUA-F 830-B (1), 1292-D (1), DBUA-F 826- A (2), Ponta dos Frades; DBUA-F 1287- A (1), DBUA-F 1027-D (9), 1189 (3), 1189 A,F (2), Pedra-que-pica, Santa Maria, Azores, Touril Complex, Lower Pliocene.
Description. Shell small, solid, moderately slender rissoiniform, slightly scalate spire. Protoconch not preserved in Azorean material. Teleoconch of six to seven initially convex, later almost flat-sided whorls, with periphery at abapical suture. Suture finely undulating, deeply impressed. Axial sculpture of close-set, slightly opisthocline to orthocline, narrow rounded ribs, slightly narrower than their interspaces, 18-22 on penultimate whorl. Spiral sculpture of very fine, close-set threads, visible only in axial interspaces and slightly stronger irregular cords over base. Last whorl about 50% of total height, weakly convex below suture, rounded at base. Aperture ovate, about 35% total height; outer lip thickened by strong labial varix, expanded abapically, smooth within, anal sinus narrow V-shaped; siphonal canal marked by small narrow notch at medial border of outer lip. Columella broadly excavated in mid-portion. Columellar and parietal callus strongly thickened forming narrow callus rim, with small tubercle formed at medial border of siphonal canal and small parietal pad developed.
Intraspecific variability. The number and thickness of the axial ribs is somewhat variable. The Azorean specimen have slightly fewer ribs (14 vs.18-22) but otherwise comparable.
Discussion. This species is characterized by the close-set, weakly opisthocline to orthocline axial ribs and poorly developed, irregular spiral sculpture. Several similar species are known from the European Neogene assemblages. Rissoina exdecussata Sacco, 1895 from the French Atlantic Pontilevian, Middle Miocene has less numerous, more strongly opisthocline axial ribs and stronger spiral sculpture. The Mediterranean Miocene to Recent R. bruguierei (Payraudeau, 1826) has even fewer axial ribs than the previous species, with stronger spiral sculpture, giving the ornament a somewhat serrated appearance. The specimen of R. bruguierei figured by Cavallo & Repetto (1992: fig. 084) is identical to our specimens from Estepona and shows a shell with numerous, almost orthocline ribs and a subobsolete spiral sculpture, quite unlike the illustrations of the Recent R. bruguierei in Giannuzzi-Savelli et al. (1997: 118, fig. 507). Specimens from the Neogene Paratethys ascribed to Rissoina pusilla by Ĥrnes (1856: 557, pl. 48, fig. 4) and Friedberg (1914: 358, pl. 20, fig. 22) represent a separate species, R. podolica Cossmann, 1921 (see Bałuk 1975: 90). As noted under the intraspecific variability, the Azorean specimens have slightly fewer ribs. They are otherwise similar to the Mediterranean specimens and bearing in mind the poor preservation of the material at hand, they are considered conspecific.
Mayer (1864: 57) described a further specimen from Bocca [sic] da Cré (= Cré; for discussion on the location of this outcrop see Madeira et al. 2007), Santa Maria Island, under the name Rissoina bronni Mayer, 1864. Judging from the original figure, this specimen is somewhat slenderer than usual for R. pusilla, not unlike one of the specimens illustrated by Chirli (2006: pl. 24, figs. 1). However, we do not formally synonymise the two as we do not have any specimen of R. pusilla from Cré.
Distribution. Lower Miocene: central Proto-Mediterranean, Italy (Zunino & Pavia 2009). Lower Pliocene: Atlantic, Santa Maria Island, Azores (Bronn in Reiss 1862; Mayer 1864); western Mediterranean, NE Spain (BL pers. comm.; NHMW coll.); central Mediterranean, Italy (Cavallo & Repetto 1992; Chirli 2006; Sosso & Dell’Angelo 2010; Tabanelli et al. 2011; Brunetti & Cresti 2018; Tabanelli et al. 2020). Upper Pliocene: central Mediterranean, Italy (Brunetti & Vecchi 2014), western Mediterranean, Estepona Basin, S. Spain (Landau et al. 2004a).
description: Published as part of Sacchetti, Claudia, Landau, Bernard & Ávila, Sérgio P., 2023, The Lower Pliocene marine gastropods of Santa Maria Island, Azores: Taxonomy and palaeobiogeographic implications, pp. 1-150 in Zootaxa 5295 (1) on pages 49-50, DOI: 10.11646/zootaxa.5295.1.1, http://zenodo.org/record/7965273