Alvania sororcula
Creators: name: Amati, Bruno
name: Appolloni, Massimo
name: Giulio, Andrea Di
name: Scuderi, Danilo
name: Smriglio, Carlo
name: Oliverio, Marco
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Rissoidae
Alvania
Alvania sororcula

description: Alvania sororcula (Granata-Grillo, 1877)
(Figs 6 A–M; 10; 16A–C; 18E, F; Table IV)
Rissoa (Alvania) sororcula Granata-Grillo, 1877a: 147
Rissoa (Alvania) sororcula var. major Granata-Grillo, 1877a: 147
Rissoa (Alvania) asperella Granata-Grillo, 1877b: 11 replacement name for Rissoa (Alvania) sororcula var. major Granata- Grillo, 1877a (new synonym)
Other references.
Alvania sororcula; Gofas & Warén, 1982: 11, figs 6, 15; Villari & Scuderi, 2017: 197, figs 10–15; Villari, 2018: 941, fig. 21 (drawing of external soft parts).
Type material. Alvania sororcula Granata-Grillo, 1877a: two syntypes (numbered 1, 2) (Monterosato coll. ex Granata-Grillo MCZR-M-22227/S), one syntype (Jeffreys coll. ex Granata-Grillo USNM, Washington) (Gofas & Warén, 1982: 11, figs 6, 15), type locality: Messina, Sicily. Alvania asperella (Granata-Grillo, 1877b ex Monterosato ms.): 3 syntypes (numbered 1, 2, 3) (MCZR-M-22069/S Monterosato coll.), type locality: Messina, Sicily.
Other material esamined. Sicily: Ustica Is., 1 sh 50 m depth (ex P. Micali coll. (Fano), DS); Palermo, 1 sh (MCZR–M–22067, Monterosato coll., as Rissoa bicingulata); off Messina, Tyrrhenian Sea, 2 sh 500 m depth (DS); Messina, S. Raineri, “Degassifica” station, 32 sh and 27 lv (DS): Catania, Acitrezza, 4 sh (DS).
Distribution. Central Mediterranean, Sicily (Fig. 10). Found amidst algae (Messina, Sicily) 1–2 m depth. Empty shells in 1–11 m depth. Found sympatric with A. scabra, A. scuderii and A. pizzinii n. sp. Shells from deeper bottoms (50–500 m) probably drifted from shallower habitat (Bonfitto et al. 1994a; 1994b; Smriglio & Mariottini 1996).
Description. Shell (Figs 6 A–N; 16A–C) small for the genus, height 1.65–2.55 mm, width 1.0– 1.38 mm, H/W ratio 1.65–2.00, ovate-conical. Protoconch (Fig. 16B) paucispiral with nucleus moderately intorted, of 1.2–1.3 whorls, height 0.275 –0.287 mm, nucleus diameter (d) 0.110 –0.125 mm, first half whorl diameter (Do) 0.200 – 0.210 mm, maximum diameter (DM) 0.350 –0.400 mm, sculpture of ca. 10 parallel rows of broadly rounded microtubercles (Fig 16B). Protoconch-teleoconch boundary well marked. Teleoconch of 2.75–3.75 slightly angled whorls, with suture impressed. Axial sculpture on the last whorl (when present) of 24–29 orthocline or slightly opisthocline ribs, plus the labial varix, narrower than the interspaces and gradually vanishing at the base. Spiral sculpture of equidistant cords, 7–9 on the last whorl, with 3–5 above the aperture and 4–5 on the base, 3–4 on the penultimate whorl, cords I and IV finer than II and II. Moderate subsutural ramp when cord I absent. Cords II and IV starting immediately after the protoconch-teleoconch boundary; cord I starting after 0.9–1.8 whorls or absent; cord III after 0.7–1.2 whorls (Table IV). Small, rounded tubercles at the intersections; interspaces quadrangular. Microsculpture of growth lines (more evident on the base) and spiral threads only on the spiral cords surface (Fig. 16C). Umbilical chink barely visible. Aperture pyriform, large, height 0.7–1.2 mm, H/Ha ratio 2.17–2.42, peristome continuous, outer varix modest, margin sharp, internally smooth. Colouration whitish-yellowish, with slightly prosocline quadrangular subsutural brown blotches; periphery and median columellar area whitish. Operculum typical for the genus, thin, corneous, paucispiral with eccentric nucleus. Body (Figs 18E, F) semi-transparent whitish with dark brown/grey areas on head and snout, darker on opercular area, fading on both sides of the body, extending only at edge of sole of foot. Yellow areas on both sides of the body merging towards the opercular area. Yellow speckles on snout, merged in short stripes on head behind and in front of eyes, forming lines along cephalic tentacles, on foot, on opercular area and on propodium, and a yellow π figure under the operculum; scattered white speckles on cephalic tentacles; 4 metapodial tentacles.
Remarks (See also Table IV and Figs 6 A–M; 10; 16A–C; 18E, F). Species not very variable (except for some large size shells corresponding to A. asperella, with on whorl more than usual, and the thickened labial varix). Granata-Grillo (1877a) described A. sororcula stating that the name was suggested by Monterosato (likely also the epithet asperella, as suggested by samples in the collection Monterosato, MCZR-M-autograph labelled ‘ R. asperella inedita foss.? Messina’: Figs 6 I–J). See under A. scabra, A. sculptilis and A. pizzinii n. sp. for differences with these species.
TABLE IV. Measurements of teleoconch and protoconch of Alvania sororcula in mm, with range, mean and standard deviation. 1 = syntype numbered 1 of A. sororcula; 2 = syntype of A. sororcula numbered 2; 3 = syntype of A. sororcula by USNM, Washington; 4 = Palermo; 5 = syntype numbered 1 of A. asperella; 6 = syntype of A. asperella numbered 2.
Alvania sororcula differs from A. lucinae by the size (H 2.55 mm in A. sororcula vs 1.95 mm in A. lucinae); the tubercles at the intersections (small, rounded nodulose A. sororcula vs spinose or almost spinose in A. lucinae); the spiral cords (all the same strength in A. sororcula vs cord III more protruding in A. lucinae).
A. sororcula differs from A. josefoi by the spiral microsculpture of the teleoconch: barely perceptible only on the spiral cords vs numerous, fine and spaced, seemingly striated threadlets in A. josefoi.
A. sororcula differs from A. scuderii by the axial riblets on the last whorl (24–29 in A. sororcula vs 15–18 in A. scuderii); the appearance of the teleoconch spiral cords (cord III at 0.7–1 whorls, cord I when present at 1.8 whorls in A. sororcula vs cord I at 1.2–1.5 whorls, cord III at 1.5–1.8 whorls in A. scuderii); the shell colouration (yellowish-whitish, with quadrangular subsutural brown blotches in A. sororcula vs brownish background with dark brown spirals in A. scuderii).
description: Published as part of Amati, Bruno, Appolloni, Massimo, Giulio, Andrea Di, Scuderi, Danilo, Smriglio, Carlo & Oliverio, Marco, 2020, Revision of the Recent Alvania scabra (Philippi, 1844) complex (Mollusca, Gastropoda Rissoidae) from the Mediterranean Sea with the description of a new species, pp. 415-458 in Zootaxa 4767 (3) on pages 431-434, DOI: 10.11646/zootaxa.4767.3.3, http://zenodo.org/record/3772979