Fluminicola fresti Hershler, Liu & Hubbart

Hershler, Robert, Liu, Hsiu-Ping & Hubbart, Niko, 2017, Two new species of Fluminicola (Caenogastropoda, Lithoglyphidae) from southwest Oregon, USA, and a range extension for F. multifarius, ZooKeys 679, pp. 1-20 : 6-11

Fluminicola fresti Hershler, Liu & Hubbart sp. n. Figs 4 E–G, 5

Types.

Holotype, USNM 1144376, diversion from Big Butte Springs through Butte Falls Hatchery, just south of Butte Falls-Fish Lake Road (Jackson County 321) and 0.16 km west of Butte Falls-Prospect Road (Jackson County 922), Jackson County, Oregon, 42.5389°N, 122.5551°W, 10/22/1994, Terrence J. Frest and Edward J. Jo hannes. Paratypes, USNM 1422223 (a large series of dry shells and alcohol-preserved specimens), from same lot.

Referred material.

OREGON. Douglas County: USNM 1297126, Trap Creek at crossing of FS4788, 0.48 km south of its confluence with the Clearwater River (43.2431°N, 122.2886°W). Jackson County. USNM 1144448, USNM 1297142, Rogue River on north side at Rogue Elk County Park, east of Rogue Elk, south of OR62 (42.6618°N 122.7524°W), USNM 1144532, USNM 1297143, Vine Creek on east side of McNeil Road (42.6270°N, 122.6722°W), USNM 1144525, USNM 1297144, Rogue River, upriver from Casey State Park boat ramp, west of McLeod (42.6591°N, 122.6993°W), USNM 1297145, Mill Creek at Mill Creek Campground off OR62 on FS030, ca. 5.6 km northeast of Prospect (42.7937°N, 122.4679°W), USNM 1144901, USNM 1145101, USNM 1145102, USNM 1297146, Evergreen Spring above Lost Creek Lake (42.7026°N, 122.6090°W), USNM 1297147, spring outflow, at foot bridge crossing, Joseph Stewart State Park (42.6810°N, 122.6216°W), USNM 1297149, spring outflow, first crossing above foot bridge, Joseph Stewart State Park (42.6811°N, 122.6204°W), USNM 1297150, Lost Creek at BLM 34-2E-8 (Medco A Road) crossing (north side), south of Joseph Stewart State Park (42.6570°N, 122.6152°W), USNM 1144528, USNM 1297152, Middle Fork Lost Creek at BLM 34-2E-8 (Medco A Road) crossing (east side), south of Joseph Stewart State Park (42.6571°N, 122.6150°W), USNM 1297153, Clark Creek collected east of BLM 34-2E-9.02 crossing off Clark Creek Road (BLM 34-2E-7) (42.6305°N, 122.5865°W), USNM 1144526, USNM 1297154, spring below (northeast of) BLM 33-2E-13.02, 0.32 rd.km off of BLM 33-2E-13.01, west of Smith Creek (42.7015°N, 122.5347°W), USNM 1144531, USNM 1297155, southern-most spring of three on west side of BLM 33-3E-28.01, 0.8 rd. km north of BLM 33-3E-34 junction, east of Reinecke Burn (42.6733°N, 122.4749°W), USNM 1297156, diversion from Big Butte Springs through Butte Falls Hatchery, USNM 1144375, USNM 1297157, Whiskey Spring at Whiskey Spring Campground on FS100 off FS37 (42.4949°N, 122.4151°W), USNM 1144533, USNM 1144534, USNM 1297158, spring in Wasson Canyon on south side of Wasson Canyon Creek above (east of) BLM 36-2E-19.2 off of BLM 36-2E-26 (42.4240°N, 122.5206°W).

Diagnosis.

A small to medium-sized Fluminicola (2.3-5.5 mm shell height) having a trochoidal to ovate-conic shell and small, gently tapered penis. Differs from closely similar and geographically proximal F. multifarius in the hooked shape of the anterior end of the osphradium, larger number of ctenidial (gill) filaments, smaller seminal receptacle, and in its mtDNA sequences.

Description.

Shell (Fig. 5 A–D) trochoidal to narrow-conic, whorls 3.5-4.0. Teleoconch whorls medium convex, sometimes weakly shouldered. Aperture ovate, slightly angled above; inner lip complete, variably thickened and reflected, sometimes forming a rather wide parietal-columellar shelf that sometimes covers the umbilical region. Outer lip thin, prosocline. Umbilicus very small or absent, umbilical region sometimes excavated. Shell white, periostracum brown, sometimes covered with thick black deposits. Shell measurements and whorl count data are summarized in Table 1.

Operculum (Fig. 5 E–F) as for genus; muscle attachment margin thickened on inner side. Radula (Fig. 5 G–I) as for genus; dorsal edge of central teeth concave, lateral cusps two–five, basal cusp one–two. Lateral teeth having two–three cusps on inner side and three–four cusps on outer side; length of outer wing 175-185% length of cutting edge. Inner marginal teeth with 23-31 cusps, outer marginal teeth with 27-40 cusps. Radula data are from USNM 1422223, USNM 1144426.

Snout, cephalic tentacles, pallial roof, visceral coil usually medium pigmented (brown); foot varying from near pale to medium pigmented along anterior edges. Distal section of penis having dense core of internal black pigment. Ctenidial filaments 21-24 (N = 5), lateral surfaces smooth. Anterior end of osphradium distinctly hooked (not illustrated). Glandular oviduct and associated structures shown in Figure 4 E–F. Coiled oviduct circular, proximal arm kinked, posterior arm sometimes having small pouch containing sperm. Bursa copulatrix large, reniform, partly overlapped by albumen gland. Bursal duct slightly shorter than bursa copulatrix, narrow. Seminal receptacle small, sac-like, almost completely overlapped by albumen gland. Albumen gland having short pallial component. Capsule gland longer than albumen gland, composed of two glandular zones. Genital aperture a small, sub-terminal pore. Penis (Fig. 4G) small, slightly curved, gently tapering, distal section abruptly narrowing to small pointed tip. Medial section having a few weak folds along inner edge. Penial duct near centrally positioned, straight, narrow.

Etymology.

This species name is a patronym (in the genitive singular) honoring recently deceased malacologist Terrence Frest for his many contributions to the documentation of molluscan biodiversity in the northwestern United States.

Distribution.

Fluminicola fresti is distributed in spring-fed habitats in the North Umpqua River drainage and in the Rogue River basin north of Little Butte Creek.

Remarks.

As noted above, the shells of F. fresti vary in overall shape and in the width of the inner apertural lip. Although this variation is generally continuous in the material that we examined, two rather distinct forms - ovate-conic with a narrow inner apertural lip (Fig. 5B) and trochoidal with a wide parietal-columellar shelf (Fig. 5C) - can be identified in one of the springs in Joseph Stewart State Park. We sequenced specimens from this locality and found that the two shell forms (samples RU18 and RU17, respectively) differed by 0.7% for COI and 1.3% for cytB, which was less than the variation within these two groups (0.2 and 1.2% for COI; and 0.2 and 1.5% for cytB, respectively). The scant genetic differentiation of the two shell forms when in sympatry provides additional evidence that they are conspecific. Additional studies incorporating rapidly evolving nuclear markers (e.g., microsatellites) may help sift through the possible explanations for the interesting variation in the shells of this species (e.g., ecophenotypic plasticity, incipient speciation). Twenty-three COI hap lotypes and 34 cytB haplotypes were detected in the sequenced specimens of F. fresti (Suppl. material 2-3, respectively).

Populations of F. fresti were referred to as the Beaverdam pebblesnail, Camp Creek pebblesnail, Clark pebblesnail, Evergreen pebblesnail, Rogue pebblesnail, Stewart pebblesnail, and Umpqua pebblesnail by Frest and Johannes (1999, 2000, 2004, 2005). In order to avoid confusion, we suggest that “Frest’s pebblesnail" be used as the common name for F. fresti .