Eremidrilus owyhee Rodriguez & Fend 2022, n. sp.

3.4. Eremidrilus owyhee n. sp.

(Figs. 2C, F; 3J–M; 6)

Holotype. USNM 1593361, whole-mounted worm, slide-mounted in Canada balsam.

Type Locality. Nevada, Elko Co., Bruneau River at Fawn Gulch, N 41.7594, W 115.5744, 1440 m altitude (3 June 2008). S. V. Fend coll.

Paratypes. USNM 1593362–1593366, from the type locality, same collection data, 2 whole-mounted, 3 dissected on slides. CASIZ 233664–233666, 2 whole-mounted, 1 dissected on slide. USNM 1593367, Owyhee River at Beaver Creek, 27 April 2004, coll. D.L. Gustafson. MNCN 16.03 /3151, 1 transversely sectioned from Owyhee River, at Beaver Creek, 27 April 2004, coll. D.L. Gustafson. MNCN 16.03 /3152, 1 dissected and MNCN 16.03 /3153–16.03/3154, 4 whole mounts from type locality, 3 June 2008, S. V. Fend coll.

Etymology. Named for the Owyhee River. The name was given to the river and the region in memory of three Hawaiian explorers lost in the region in 1819–20, during Mackenzie‘s Snake expedition (en.wikipedia.org/wiki/Owyhee_County,_ Idaho, last edited on 15 December 2021).

Other material. Nevada, Elko Co., several localities, in authors’ collections. Bruneau River at Fawn Gulch (type locality), 3 June 2008, S. Fend coll., 2 dissected, 21 whole mounts. Bruneau River at Cottonwood Creek, N 41.7737, W 115.5823, 1768 m altitude, 15 July 2004, 2 whole-mounted. Owyhee River at Beaver Creek, 27 April 2004, one whole-mounted, 3 dissected, 1 transversely sectioned. Owyhee River below Wildhorse Reservoir, N 41.7259 W 115.896, 1828 m altitude, 27 March 2003, one dissected. Idaho, Camas Co., Big Smoky Creek N 43.6076, W 114.8995, 22 August 2005, 3 whole mounts. All collected by D. L. Gustafson unless otherwise indicated.

Description (from type locality population). Segments 55–90. Length of fixed worms 10–19 mm, body diameter in X, 0.31–0.58 mm. Proboscis (100) 250−425 µm long, 40−64 µm diameter at middle. Segmentation distinct, with secondary annulus well marked from III to postclitellar segments (XIII−XIV) (Fig. 2C). All chaetae simplepointed and sigmoid; in anterior part of the body 100–147 µm long, those in ventral bundles usually slightly longer than dorsals, short in II 72−96 µm, and gradually longer to VII or VIII, nodulus at 0.3–0.4 chaetal length from the tip, sometimes about median in segment II. Chaetae in middle and posterior segments of similar length (112−149 µm), with nodulus distal (at 0.3–0.4 from distal end), dorsals and ventrals about equal in length (Fig. 2F). Epidermis smooth, 6–18 µm high, slightly thicker at the clitellum (14–26 µm), which extends from X to anterior part of XIII, and is formed by irregularly organized epidermal glands. Pharyngeal glands dorsal and ventral to the gut in segments (IV)V−VII; ventral lobes may be present in VIII. Nephridia with the ectal duct usually ending in a short, expanded vesicle (40–62 µm long, 25–35 µm wide) (Fig. 6H); nephridia absent in preclitellar segments. Male pores slightly lateral to ventral chaetal lines, in the posterior part of segment X, at about midway between ventral chaetae and posterior septum, opening on conical to almost cylindrical porophores of variable size (Figs. 2C; 3J–L; 6A–C), probably depending on fixation or the degree of extension (44−120 µm basal and 29–70 µm apical diameter; 80–170 µm long). Spermathecal pores just below the lateral line (Figs. 2C; 3J, M; 6A, D). Female pores in 11/12.

Sperm sacs usually extend anteriorly to VIII, posteriorly to XIV−XVI; egg sacs to XV−XVIII. Vasa deferentia 12−19 µm wide and about 220−360 µm long; posterior vas forms a loop in XI (in the space of the secondary annulation of segment XI), and both vasa join the atrial wall at about the apical third of the atrium. Atrium elongated, cylindrical (208–350 µm long), very narrow (22−59 µm diameter), including muscle layer (1–6 µm thick) and lining cells (7−10 µm high). Atrial ampulla usually bent and sparsely covered by discrete clumps of prostatic cells (25−55 µm high) (Figs. 3J–L; 6C). Male duct extends through the porophore, with numerous circular muscle fibres attached to the epithelium of the duct (Figs. 3K; 6C).

Large spermathecal ampullae, about 1.5 to 2 times as long as wide (65−275 µm wide; 105−460 µm long), in segment XI or may pass to the segment XII. Spermathecal ducts short (70−170 µm long) and tapered (30−65 µm wide at the middle); long transverse muscles join the spermathecal pore to the dorsal body wall; when contracted, the spermathecal pore opens within a lateral fold of the body wall (Figs. 3J; 6F, G). Sperm in ampulla forms a circular bundle that occupies most of the lumen, and part of the spermatozoids are oriented toward the epithelial cells near the duct (Fig. 6E).

(a)

diameter of the male porophore measured at the ectal end

Remarks. Eremidrilus owyhee n. sp. is easily distinguished from all other congeneric species by the narrow atrium with well-separated prostatic glands, and by the long, protrusible male porophore (Table 2). Unlike other species in the Snake River drainage, E. owyhee n. sp. has one pair of spermathecae (in XI). The spermathecal pores are at the lateral line, resembling the position in the California species E. felini and E. ritocsi (Fend & Rodriguez 2003), but differing from all of the other known species in the genus. When retracted, the spermathecal pore opening within a lateral fold is reminiscent of the spermathecal sac of E. felini, although it is shallower and never forming a porophore-like structure when unretracted. The gut of the examined individuals contains detritus mixed with large sand grains and some diatoms.

The Bruneau and Owyhee Rivers are tributaries to the Snake River, both joining it in southwestern Idaho. Most of the E. owyhee records are from upper reaches of these rivers, geographically very close to each other (see below). Both drainages are in an arid plateau region, and channels are in deeply incised canyons, with relatively sparse vegetation. Sampling sites have permanent flow throughout the year. Big Smoky Creek is more distant (approximately 200 km North), and drains to the Boise River, yet another Snake River tributary. The limited specimens appeared similar to those from the type locality, despite their proximity to type localities of two other Eremidrilus species (E. artzaini and E. humboldti) in more upstream Snake tributaries. A single, partially mature specimen resembling E. owyhee was also collected in the nearby Marys River, which drains southward to the endorheic Humboldt River (Nevada). The collection localities are intermediate between the Pacific Coastal drainages (having species with only one spermathecal segment) and the Idaho and eastern sites (having species with two spermathecal segments).