Pyrgulopsis castaicensis, Hershler, Robert & Liu, Hsiu-Ping, 2010

Hershler, Robert & Liu, Hsiu-Ping, 2010, Two new, possibly threatened species of Pyrgulopsis (Gastropoda: Hydrobiidae) from southwestern California, Zootaxa 2343, pp. 1-17 : 6-10

Pyrgulopsis castaicensis sp. nov.

( Figs 3–5 )

Types. Holotype ( Fig. 3 A), USNM 1120442, Middle Canyon Spring, ca. 1.46 km southwest of Castaic Junction, Santa Clara River drainage, Los Angeles County, California (351542 E, 3810993 N), 21/x/2008, Robert Hershler. Paratypes, USNM 1132532 (from same lot, 60 dry shells).

Etymology. A geographic epithet referring to the distribution of this species near the mouth of Castaic Creek.

Referred material. CALIFORNIA. Los Angeles County. USNM 1097788., Middle Canyon Spring, ca. 20 m below spring source, 351596 E, 3810937 N, 26/vi/2006, Mark Elvin & Douglas Threloff.

Diagnosis. A small species of Pyrgulopsis having a medium-spired, sub-globose to narrow-conic shell with medium to highly convex whorls. Penis having a small lobe and short filament; penial ornament consisting of a well developed terminal gland.

Description. Shell ( Fig. 3 A–C) usually ovate- or narrow-conic, rarely sub-globose (smallest individuals); height about 1.3–2.5 mm; whorls 3.5–4.5. Periostracum tan, thin. Protoconch ( Fig. 3 D) near planispiral, about 1.3 whorls, diameter about 365 µm, initial 0.5 whorl ( Fig. 3 E) weakly wrinkled, otherwise smooth. Teleoconch whorls medium or highly convex, strongly shouldered; sculpture of well developed, collabral growth lines; last 0.5 whorl usually slightly loosened. Aperture medium-sized, ovate, slightly angled adapically. Inner lip usually disjunct, rarely narrowly adnate; thin or slightly thickened internally, without columellar shelf; outer lip thin, orthocline or weakly prosocline. Umbilicus perforate in specimens having an adnate inner lip.

Operculum ( Fig. 3 F) thin, flat, light amber (nuclear region slightly darker), multispiral with sub-central nucleus; last 0.5–0.75 whorl weakly frilled on outer side; attachment scar border on inner side of operculum ( Fig. 3 G–H) nearly smooth to slightly thickened almost all around. Radula taenioglossate ( Fig. 4 A), having about 43 well-formed rows of teeth. Central teeth ( Fig. 4 B) about 17 µm wide, cutting edge concave; lateral cusps 4–6; central cusp narrow, pointed, parallel-sided proximally; basal cusp 1, small; basal tongue Vshaped, about as long as lateral margins. Lateral tooth ( Fig. 4 C) face rectangular; central cusp large, narrow, pointed; lateral cusps 3–4 (inner), 4–5 (outer); outer wing medium width, flexed, straight, about 250% length of cutting edge; basal tongue weakly developed. Inner marginal teeth ( Fig. 4 C–E) having 22–26 cusps. Outer marginal teeth ( Fig. 4 F) having 24–28 cusps; inner edge having long, rectangular wing. Radular data were from USNM 1097788.

Head-foot generally lightly pigmented. Cephalic tentacles pale or having central, longitudinal brown streak. Snout light brown or black, pigment weaker or absent centrally; distal lips pale. Sole of foot pale. Pallial roof, visceral coil dark brown or black dorsally. Ctenidium well developed, positioned a little in front of pericardium; ctenidial filaments about 15, rather small, taller than wide, without pleats. Osphradium narrow or elongate, positioned centrally along ctenidium. Prostate gland small, bean-shaped, about 33% of length in pallial roof. Anterior vas deferens opening from ventral edge of prostate gland a little in front of (posterior) pallial wall, section of duct on columellar muscle having prominent bend. Penis ( Fig. 5 A–B) medium sized; base rectangular, slightly expanded distally; inner edge having weak folds; filament short, narrow, tapering, slightly oblique; lobe short, broad, slightly tapered distally, oblique. Terminal gland usually narrow, crescent-shaped, overlapping ventral and (to a lesser extent) dorsal edges of lobe; gland divided into two small, circular units in one specimen. Penial duct narrow, nearly straight. Proximal half of penial filament containing a dense core of black pigment; penis otherwise pigmented with scattered black granules. Female glandular duct and associated structures shown in Figure 5 C–E. Coiled oviduct a medium-sized, posterioroblique loop. Bursa copulatrix small, ovate, horizontal, largely overlapped by albumen gland. Bursal duct slightly longer and considerably narrower than bursa, opening from distal edge, partly embedded in albumen gland. Seminal receptacle small to medium-sized, sac-shaped, sometimes folded, positioned near anteroventral edge of bursa, duct short to medium length. Albumen gland longer and wider than capsule gland, having very short pallial section. Capsule gland composed of two tissue sections. Genital aperture a terminal slit.

Shell measurements (mean + standard deviation in parentheses): height 1.93–2.45 mm (2.16+0.15), width 1.29–1.65 mm (1.44+0.10), body whorl height 1.43–1.79 mm (1.62+0.09), body whorl width 1.13–1.44 mm (1.27+0.08), aperture height 0.82–1.03 mm (0.90+0.06), aperture width 0.75–0.91 mm (0.82+0.04), shell width/height 0.61–0.71 (0.67+0.03), body whorl height/shell height 0.69–0.79 (0.75+0.02), aperture height/ shell height 0.36–0.46 (0.42+0.02) (from paratype lot, USNM 1132532, n = 30).

Measurements of holotype: height 2.50 mm, width 1.70 mm, body whorl height 1.81 mm, body whorl width 1.39 mm, aperture height 1.05 mm, aperture width 0.92 mm, shell width/height 0.68, body whorl height/shell height 0.72, aperture height/shell height 0.42, 4.25 whorls.

Distribution, habitat and conservation status. Pyrgulopsis castaicensis appears to be endemic to the type locality area based on the first author’s regional fieldwork and study of pertinent institutional collections, and recent surveys of proximate portions of the Santa Clara River basin ( Swift 2009). The small, shallow spring-fed stream inhabited by this species is situated on a terrace of the Santa Clara River and shaded by a tall canopy and dense riparian vegetation (Dudek 2007). Pyrgulopsis castaicensis was rather abundant on plant debris and the sandy bottom of the stream.

The type locality area is located along the northeastern edge of the property slated for development. The resources management plan for this development incorporates an adaptive management framework to ensure protection of the spring habitat of P. castaicensis (USACE & CDFG 2009); the California Department of Fish and Game is overseeing the implementation of the plan and the conservation program associated with the development. Although its spring habitat will be protected under this plan as a “unique landscape feature,” P. castaicensis nonetheless may be threatened by the extensive alteration of local topography and watershed associated with this development (GSI Water Solutions Inc. 2007; Dudek 2008a).

Remarks. The spring that constitutes the type locality of P. castaicensis is not shown on USGS topographic or BLM land management maps, but has been referred to as Middle Canyon Spring in numerous documents relating to the Newhall Ranch development plan (e.g., Dudek 2007; Dudek 2008b; USACE & CDFG 2009). The species described herein as P. c a s t a i c e n s i s was mentioned (as an undescribed species of Pyrgulopsis ) in several of these documents (e.g., Dudek 2007; Swift 2009; USACE & CDFG 2009).

The penial ground plan of P. castaicensis – narrow, distally bifurcate, ornamented with a terminal gland along the edge of the lobe – is a common ( Hershler & Sada 2002) and apparently iteratively evolved ( Liu & Hershler 2005) morphology within the genus that is shared by two congeners that are distributed in fairly close proximity (ca. 45–150 km) to this new species ( P. micrococcus , eastern Transverse Ranges; P. stearnsiana , lower Santa Clara River basin). Pyrgulopsis castaicensis is distinguished from P. micrococcus by its larger terminal gland (on the penis), simple oviduct coil (lacking a proximal kink or loop), more anteriorly positioned seminal receptacle, and mtCOI sequences (6.1–9.3% divergence) (see Hershler & Sada 1987; Hershler 1989; Hershler 1994 for morphological descriptions of the latter). Pyrgulopsis castaicensis is differentiated from P. stearnsiana by its more convex teleoconch whorls, larger penial lobe, larger terminal gland, simple oviduct coil, shorter pallial section of albumen gland and smaller (relative to bursa copulatrix) seminal receptacle (see Hershler 1994 for description of the latter). Pyrgulopsis castaicensis was most similar in its mtCOI sequences to P. stearnsiana from the San Francisco Bay area (3.50% divergence) among all of the samples included in our study and differed from other specimens of this species by 3.8–8.2%. This level of sequence divergence falls within the range previously documented for>60 other species of Pyrgulopsis (1.1– 13.1%; Liu & Hershler 2005). Pyrgulopsis castaicensis thus is recognized as a new species because it is morphologically diagnosable and because our sequence data indicate that it is phylogenetically independent and substantially divergent.

Figures

FIGURE 3. P. castaicensis sp. nov. A – C. Shells. Scale = 1.0 mm. A. Holotype, USNM 1120442. B – C. Paratypes, USNM 1132532. D. Shell apex, USNM 1132532. Scale = 100 µm. E. Close-up of protoconch sculpture, USNM 1132532. Scale = 100 µm. F – H. Opercula, USNM 1132532. Scale = 250 µm. F. Outer side, showing frilled whorl. G – H. Inner side, showing variation in thickening of attachment scar margin.

FIGURE 4. P. castaicensis sp. nov., USNM 1097788. A. Portion of radula ribbon. Scale = 10 µm. B. Central radular teeth. Scale = 2 µm. C. Lateral and inner marginal teeth. Scale = 10 µm. D – E. Inner marginal teeth. Scales = 10 µm. F. Outer marginal teeth. Scale = 10 µm. Wg = wing.

FIGURE 5. P. castaicensis sp. nov., USNM 1097788. Scale = 0.25 mm. A – B. Penis. A. Dorsal surface. B. Ventral surface of distal portion, showing extent of terminal gland. C. Female glandular oviduct and associated structures (viewed from the left side). D. Bursa copulatrix and its duct. E. Seminal receptacle and its duct. Ag = albumen gland, Bu = bursa copulatrix, Cd = common duct of seminal receptacle and oviduct, 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, Tg = terminal gland, Vc = ventral channel, Vg = ventral gland.