Pyrgulopsis fresti, Hershler, Robert & Liu, Hsiu-Ping, 2009

Hershler, Robert & Liu, Hsiu-Ping, 2009, New species and records of Pyrgulopsis (Gastropoda: Hydrobiidae) from the Snake River basin, southeastern Oregon: further delineation of a highly imperiled fauna, Zootaxa 2006, pp. 1-22 : 9-12

Pyrgulopsis fresti sp. nov.

( Figs 3–5 )

Types. Holotype ( Fig. 3 A), USNM 1102148, Tudor Warm Springs, east side of Owyhee River, second spring from north, Malheur County, Oregon (484936 E, 4708680 N), 11/v/2007, Robert Hershler, William H. Clark & Shaney Rockefeller. Paratypes, USNM 1116914 (from same lot, 751 specimens); USNM 1102161 (453 specimens), 12/v/2007, Robert Hershler & William H. Clark.

Etymology. In honor of recently deceased colleague Terrence J. Frest, who made tremendous contributions to the study and conservation of the nonmarine mollusks of the Pacific Northwest through his extensive fieldwork, documentation of previously little known faunas, and staunch environmental advocacy.

Referred material. OREGON. Malheur County. USNM 1097817, spring tributary to Owyhee River upflow from Tudor Warm Springs, 484401 E, 4707220 N, 11/x/2006. USNM 1097818, spring complex along Owyhee River upflow from Tudor Warm Springs, 483313 E, 4705913 N, 11/x/2006. USNM 873474, above Three Forks, T. 35 S, R. 45 E, E 1/2 SW 1/4 sec. 3, 15/i/1987. USNM 892084, Tudor Warm Springs, east side of river, second spring from north, 485020 E, 4708400 N, 23/ix/1989. USNM 1071457, ibid., 485060 E, 4708420 N, 25/ix/2002. USNM 1102151, Tudor Warm Springs, east side of river, third spring from north, 484935 E, 4708661 N, 12/v/2007. USNM 892082, Tudor Warm Springs, east side of river, fourth spring from north, 485040 E, 4708330 N, 23/ix/1989. USNM 1092856, ibid., 484949 E, 4708640 N, 19/vii/2006. USNM 1102147, ibid., 484950 E, 4708634 N, 11/v/2007. USNM 892083, Tudor Warm Springs, west side of river, first spring north of mouth of Warm Springs Canyon, 484920 E, 4708520 N, 23/ix/1989. USNM 1092860, Tudor Warm Springs, west side of river, second spring north of mouth of Warm Springs Canyon, 484853 E, 4708749 N, 19/vii/2006. USNM 1102146, ibid., 484851 E, 4708753 N, 11/v/2007.

Diagnosis. A small species of Pyrgulopsis having a low-spired, globose or trochiform shell with medium to highly convex whorls. Penis having a small lobe and short filament; penial ornament consisting of a large, disc-shaped ventral gland.

Description. Shell subglobose or trochiform ( Fig. 3 A–C); height about 1.3–2.7 mm; whorls 3.0–4.0. Periostracum light brown, thin. Protoconch near planispiral, often eroded, about 1.3 whorls, diameter about 330 µm, surface weakly wrinkled near apex, otherwise smooth ( Fig. 3 D–E). Teleoconch whorls medium or highly convex, variably shouldered; sculpture of strong, collabral growth lines. Aperture large, broadly ovate, slightly angled adapically. Inner lip usually adnate, rarely slightly disjunct, often nearly straight, thin or slightly thickened internally, without columellar shelf; outer lip thin, prosocline. Umbilicus narrow or perforate.

Shell measurements (mean ± standard deviation in parentheses): height 2.06–2.67 mm (2.24+0.14), width 1.79–2.26 mm (1.98+0.12), body whorl height 1.87–2.27 mm (2.02+0.10), body whorl width 1.38–1.71 mm (1.54+0.08), aperture height 1.18–1.63 mm (1.33+0.09), aperture width 1.09–1.34 mm (1.20+0.06), shell width/height 0.82–0.97 (0.88+0.04), body whorl height/shell height 0.85–0.94 (0.90+0.02), aperture height/ shell height 0.55–0.65 (0.60+0.03) (paratypes, USNM 1116914, n = 29).

Measurements of holotype: height 2.67 mm, width 2.03 mm, body whorl height 2.16 mm, body whorl width 1.74 mm, aperture height 1.30 mm, aperture width 1.22 mm, shell width/height 0.76, body whorl height/shell height 0.81, aperture height/shell height 0.49, 4.0 whorls.

Operculum thin, flat, amber-colored, multispiral with eccentric nucleus; last half whorl weakly frilled on outer side ( Fig. 3 F); inner side sometimes having weakly rimmed along outer edge, attachment scar border smooth to slightly thickened almost all around ( Fig. 3 G–H). Radula taenioglossate ( Fig. 4 A), with about 55 well-formed rows of teeth. Central teeth ( Fig. 3 B) about 33 µm wide, cutting edge strongly concave; lateral cusps 5–8; central cusp narrow, pointed, sometimes parallel-sided proximally; basal cusp 1, small; basal tongue U-shaped, about as long as lateral margins. Lateral tooth ( Fig. 4 C) face rectangular, angled; central cusp large, pointed, parallel-sided proximally; lateral cusps 2–4 (inner), 3–5 (outer); outer wing rather broad, straight, about 145% length of cutting edge; basal tongue weakly developed. Inner marginal teeth having 15–20 cusps ( Fig. 4 D). Outer marginal teeth having 15–21 small cusps ( Fig. 4 E); inner edge having long, rectangular wing ( Fig. 4 F).

Head-foot generally dark brown. Cephalic tentacles light brown dorsally, proximal half sometimes darker, ventral surfaces nearly pale. Distal lips of snout pale. Sole of foot pale or grey. Pallial roof, visceral dark brown or black dorsally. Ctenidium well developed, positioned a little in front of pericardium; ctenidial filaments about 18, rather small. Osphradium narrow, positioned posterior to middle of ctenidium. Prostate gland small, bean-shaped, almost entirely visceral. Anterior vas deferens opening from ventral edge of prostate gland a little in front of pallial wall, section of duct on columellar muscle having prominent bend. Penis ( Fig. 5 A–B) large, base rectangular, inner edge weakly folded proximally; filament short, tapering, slightly oblique, distal tip sometimes folded; lobe short, rectangular or tapering, horizontal or slightly oblique. Ventral gland large, disc-shaped, slightly elevated, composed on numerous small units, proximally positioned ( Fig. 5 B). Penial duct very narrow, nearly straight. Penial filament containing a dense core of black pigment; penis otherwise pigmented with a few black granules distally. Female glandular oviduct and associated structures shown in Figure 5 C–D. Coiled oviduct a circular or vertical loop. Bursa copulatrix small, ovate, horizontal or slightly oblique, largely or entirely overlapped by and sometimes partly embedded within albumen gland. Bursal duct slightly shorter to slightly longer than bursa, opening from distal edge. Seminal receptacle absent. Albumen gland longer than capsule gland, entirely visceral or with very short pallial section. Capsule gland composed of two distinct tissue sections. Genital aperture a terminal slit.

Distribution and habitat. Pyrgulopsis fresti is distributed along a short reach of the Owyhee River above Three Forks ( Fig. 1 ). This species was previously thought to be endemic to Tudor Warm Springs ( Frest & Johannes 1995, as Owyhee hot springsnail). The two additional populations reported herein were discovered during a survey that was focused on riverine hydrobiids ( Myler & Hopper 2006). Additional surveys of seeps and springs along the Owyhee River in southeastern Oregon will be needed to accurately delineate the geographic range of this species. Pyrgulopsis fresti lives on loose cobble and basalt rock faces in very shallow, thermal (ca. 24–33º C.) spring runs and is sometimes found in sympatry with P. owyheensis ; additional ecological details are provided by Frest & Johannes (1995).

Remarks. Pyrgulopsis fresti is readily distinguished from other congeners living in the Owyhee River basin and adjacent drainages by its broad, low-spired shell and distinctive glandular ornament on its penis. It also differs from these species in lacking a seminal receptacle, a character which it uniquely shares with P. arizonae ( Taylor, 1987) (see Taylor 1987, fig. 15d, e), and in its mitochondrial DNA sequences (Table 2). Pyrgulopsis fresti is further differentiated from P. bruneauensis Hershler, 1990 , the only other congener endemic to thermal springs in the Snake River basin, by its larger penial lobe and shorter penial filament (compare Fig. 5 B with Hershler, 1990, fig. 6). The COI sequence divergence between these two species is 7.7–8.9% (Liu & Hershler unpublished). Eight congeners which live in drainages well to the south of the Snake River basin have penial ornament similar to that of P. f re s t i ( Hershler & Sada, 2002:271, “species group 2”). As noted in the Diagnosis (above), one of these species ( P. arizonae ) uniquely shares with P. fresti the absence of a seminal receptacle. However, the COI sequence divergence between these two species is 8.8–9.2% (Liu & Hershler unpublished), which suggests that they are not close relatives. None of the remaining seven species is closely related to P. fresti either based on our molecular evidence (Liu & Hershler unpublished). Pyrgulopsis fresti appears to be another example of a morphologically and genetically divergent, narrowly endemic springsnail lineage associated with thermal spring habitats ( Liu & Hershler 2005).

Specimens from the Tudor Warm Springs localities varied somewhat in terms of spire height, whorl convexity and thickening of the inner shell lip ( Fig. 3 A–C). The few individuals collected from the two upriver sites (not figured) differed from the above in having weaker shouldering of the teleoconch whorls. The single sequenced specimen from the west side of the river at Tudor Warm Springs (IP69) differed from those collected on the east side (IP68, P176, P210, P212) by 2.1% sequence divergence and from specimens obtained from the two upriver sites (P207, P208) by 2.0% (1.6–2.5%). (The other two groups differed from each other by only 0.9% [0.6–1.2%].) This level of divergence falls within the range of values documented for other congeners (1.1-13.1% for COI, Liu & Hershler 2005). Additional sequencing may provide the basis for recognizing the western Tudor Warm Springs population as a distinct conservation unit.

Radular count data were from USNM 1092860, USNM 1102161.

Figures

FIGURE 1. Map showing the distributions of Pyrgulopsis species in southeastern Oregon. Arrows indicate previously documented localities; all others are newly reported herein. Some of the symbols refer to multiple, closely proximal localities.

FIGURE 3. P. f re s t i sp. nov. A – C. Shells. Scale bar = 1.0 mm. A. Holotype, USNM 1102148. B. Paratype, USNM 1116914. C. USNM 1092860. D. Shell apex, USNM 1116914. Scale bar = 100 µm. E. Close-up of protoconch sculpture, USNM 1116914. Scale bar = 100 µm. F – H. Opercula. Scale bar = 500 µm. F. Outer side, showing frilled whorl, USNM 1102161. G – H. Inner side, showing variation in thickening of attachment scar margin, USNM 1116914, USNM 1102161. Rm = rim.

FIGURE 4. P. fresti sp. nov., USNM 1102161. A. Portion of radula ribbon. Scale bar = 20 µm. B. Central radular teeth. Scale bar = 10 µm. C. Lateral and inner marginal teeth. Scale bar = 10 µm. D. Inner marginal tooth. Scale bar = 10 µm. E. Outer marginal teeth. Scale bar = 10 µm.. F. Outer marginal tooth, showing outer wing. Scale bar = 10 µm. Wg = wing.

FIGURE 5. P. f resti sp. nov., USNM 1102161. A – B. Penis. Scale bar = 0.5 mm. A. Dorsal surface. B. Ventral surface. C. Female glandular oviduct and associated structures (viewed from the left side). Scale bar = 0.5 mm. D. Bursa copulatrix and its duct. Scale as in “ C. ” Ag = albumen gland, Bu = bursa copulatrix, Cg = capsule gland, Co = coiled oviduct, Dbu = bursal duct, Ga = genital aperture, Pd = penial duct, Pf = penial filament, Pl = penial lobe, Pw = posterior wall of pallial cavity, Vc = ventral channel, Vg = ventral gland.