Pyrgulopsis micrococcus (Pilsbry, 1893)

Hershler, Robert, Liu, Hsiu-Ping & Bradford, Corbin, 2013, Systematics of a widely distributed western North American springsnail, Pyrgulopsis micrococcus (Caenogastropoda, Hydrobiidae), with descriptions of three new congeners, ZooKeys 330, pp. 27-52 : 38-40

Pyrgulopsis micrococcus (Pilsbry, 1893) Figs 4 G–H, 8

Amnicola micrococcus Pilsbry in Stearns 1893: 277, fig. 1 (small spring in Oasis Valley Nevada; also from Death Valley). Baker 1964: 174 (lectotype designation).

Fontelicella (Microamnicola) micrococcus . - Gregg and Taylor 1965: 109 (comb. n.).

Pyrgulopsis micrococcus . - Hershler and Thompson 1987: 29 (new combination). Hershler and Sada 1987: 788-791 (in part). Hershler 1989: 182-187 (in part). Hershler 1998: 15.

Pyrgulopsis micrococcus clade A. - Liu et al. (2003).

Types.

Lectotype, ANSP 67279; paralectotypes, ANSP 368399, USNM 123622 (from same lot).

Other material examined.

NEVADA. Nye County: USNM 847246, springs at Springdale (37.03049°N, 116.75117°W), BellMNH 20674, spring east of Springdale (37.03858°N, 116.71730°W), BellMNH 20671, BellMNH 20672, BellMNH 20673, BellMNH 20739, USNM 850297, USNM 857961, USNM 874778, USNM 894330, USNM 905091, USNM 1002348, USNM 1004184, USNM 1004185, USNM 1068649, USNM 1068650, USNM 1068794, spring at Fleur de Lis Ranch, ca. 0.8 km south of Springdale (37.01700°N, 116.73300°W), BellMNH 20670, USNM 874771, USNM 1002349, USNM 1004182, USNM 1004183, USNM 1146338, Goss Springs (36.99906°N, 116.70725°W), BellMNH 20669, BellMNH 20774, Ute Springs (36.95729°N, 116.71648°W), BellMNH 20667, BellMNH 20740, USNM 874758, Revert Springs (36.91795°N, 116.74397°W).

Revised diagnosis.

A medium-sized congener (maximum shell height, 4.4 mm) having a broadly to elongate conic shell. Differentiated from similar regional species by the large size of the gland on the ventral surface of the penis.

Description.

Shell (Fig. 8 A–D) broadly to narrow-conic, whorls 3.50-5.0. Teleoconch whorls weakly to strongly convex, sutures impressed. Aperture ovate, parietal lip complete, usually disjunct, last 0.25-0.5 whorl often loosened behind aperture, umbilicus small. Outer lip usually thin, orthocline. Sculpture of faint, irregular spiral striae.

Operculum (Fig. 8 E–F) as for genus; edges of last 0.5 whorl frilled on outer side; muscle attachment margins thickened on inner side. Radula (Fig. 8 G–I) as for genus; dorsal edge of central radular teeth concave, lateral cusps five–eight, basal cusp one. Lateral teeth having three–four cusps on inner sides and four–five cusps on outer sides. Inner marginal teeth with 18-23 cusps, outer marginal teeth with 21-29 cusps. Radula data are from USNM 847246.

Penis (Fig. 4 G–H) medium-sized; filament short, narrow, tapering, slightly oblique; lobe small, tapering, horizontal; a large (terminal) gland (borne on a raised swelling) present on ventral surface of penis, extending from near mid-length almost to tip of lobe (90/90 specimens), one–two additional small glands sometimes present on ventral surface of lobe (8 specimens), one specimen had a glandular dot on the dorsal surface near the base of the filament. Penial data are from BellMNH 20663, BellMNH 20669, BellMNH 20744.

Distribution.

Several groups of springs in Oasis Valley, upper Amargosa River basin (M1, M31, Fig. 2).

Remarks.

Pilsbry (in Stearns 1893; also see Stearns 1901) listed a single “type” lot for Pyrgulopsis micrococcus , [USNM] 123622, which is composed of six dry shells. Baker (1964) subsequently designated ANSP 67279a as the “type” without explaining his rationale for this action. ANSP 67279a (Fig. 8A) closely conforms to Pilsbry’s description and figure and is also very similar to the USNM type material ( Hershler and Sada 1987, fig. 8a). The labels associated with ANSP 67279a indicate that it was part of the original collection of Pyrgulopsis micrococcus (made by C. Hart Merriam) and this lot was almost certainly known to Pilsbry, who was the curator of mollusks at the Academy of Natural Sciences during the time period when his description was prepared and published. Based on this evidence we conclude that ANSP 67279a is part of the type series and thus Baker’s subsequent lectotype designation is valid.

Pyrgulopsis micrococcus was resolved in the Bayesian tree as sister to an undescribed species from the Amargosa Canyon, south of Tecopa (Fig. 1). Specimens assigned to Pyrgulopsis micrococcus vary somewhat in size and shell shape, but are closely similar both genetically ( Liu et al. 2003) and in penial morphology.