Pisidium vile Pilsbry 1897
Creators: name: Ituarte, Cristián
name: Korniushin, Alexei Victor
Publisher: name: Zenodo
Year: 2006
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Bivalvia
Veneroida
Sphaeriidae
Pisidium
Pisidium vile

description: Pisidium vile Pilsbry, 1897
Figures 7, 8
Pisidium vile Pilsbry, 1897:292, pl. 6, figs. 17–20.
Description: Shell small (maximum observed L= 2.85, average= 2.2 ± 0.33), high (I H/L varying among localities between 85 ± 2 and 89.2 ± 2.3), inflated (Ci varying among localities between 79 ± 4 and 82.3 ± 4.6). Beaks wide at base, inflated and high, well visible over dorsal margin, sub-central or slightly displaced posteriorly (located at about 57–60% of L). Shell outline trapezoid, anterior end slightly protruded, posterior end nearly straight, truncated. Dorsal margin short, markedly curve, ventral margin widely curve. Shell surface brilliant, white or yellowish, with somewhat regularly well marked commarginal striae (Fig. 7A, B, D). Hinge plate solid (Fig. 7E, F). Hinge line moderately long (Hil/L varying among localities between 56 ± 1.6 and 58 ± 3). Hinge: Left valve (Fig. 7E): inner cardinal tooth (C2) robust, with pointed cusp bent upward, outer cardinal (C4) slender, curved, covering C2 at posterior end; anterior (A2) and posterior (P2) lateral teeth robust with markedly displaced cusps. Right valve (Fig. 7F): cardinal tooth (C3) minute, straight at anterior half, enlarged at posterior end in a triangular cup; inner anterior (A1) and inner posterior (A1) laterals quite robust, outer lateral teeth (A3, P3) reduced in size but strong. Ligament pit enclosed, ligament slender, moderately long (Li= 20 ± 1.4), not visible from exterior. Escutcheon marked by a delicate line, anterior half slightly elevated, over the anterior half of ligament (Fig. 7C).
Anatomy: Mantle: Only the anal mantle opening present, siphon retractor muscles of the same conditions as in Pisidium sterkianum and Pisidium dorbignyi (Fig. 8A, B). Inner radial mantle muscles forming six strong, well defined, bundles, evenly distributed along the pedal slit. Muscle scars well defined only in anterior part of the shell where they are separate from the mantle line (Fig. 8C).
Gills: Only inner demibranch present. Developing brood pouch occupying the upper part of the inner demibranch, formed by 12 (in a 2.4 mm long specimen) to 17 (in a 2.75 mm long specimen) filaments (Fig. 8D). Between five and 11 embryos per pouch were found.
Nephridium: Of the closed type, with broad and rectangular dorsal lobe (Fig. 8E, F) and lateral loop visible from dorsal view.
Examined material: Uruguay: Syntypes (ANSP 70489), Arroyo Miguelete, Montevideo (34°51'29”S, 56°10'15”W); Arroyo Miguelete, Montevideo (MLP 5665). Argentina: Arroyo Miguelín, Ensenada (34° 52'33”S, 57° 52'56”W), Buenos Aires Province (MLP 5662).
Remarks: The high trapezoidal shell outline, the quite solid hinge plate and the reduced size, clearly identifies Pisidium vile and separates it from other small South American species such as Pisidium dorbignyi (with a lower shell outline and less prominent beaks) and Pisidium punctiferum Guppy, 1867 (with a somewhat subquadrangular, flatter shell). It should be noted that the concentration of mantle muscles in Pisidium dorbignyi and Pisidium vile may be associated with smaller size, however, Pisidium punctiferun, a species of comparable or even smaller size, has not less than 8 bundles of inner radial mantle muscles (Korniushin, personal observation).
description: Published as part of Ituarte, Cristián & Korniushin, Alexei Victor, 2006, Anatomical characteristics of two enigmatic and two poorly known Pisidium species (Bivalvia: Sphaeriidae) from Southern South America, pp. 33-47 in Zootaxa 1338 on page 42, DOI: 10.5281/zenodo.174347