Eremidrilus chalonensis Rodriguez & Fend 2022, n. sp.

3.2. Eremidrilus chalonensis n. sp. (Figs. 2A,D; 3A–E; 4) Holotype. USNM 1593338, whole worm, slide-mounted in Canada balsam. Type Locality. California, San Benito Co., Chalone Creek at downstream end of Pinnacles National Park, Salinas R. drainage, N 36.4512, W 121.1546, 278 m altitude (13 March 2005). S. V. Fend and P. G. Johnson coll. Paratypes. USNM 1593339–1593355. 12 whole-mounted specimens 13 March 2005; 2 sagitally and 2 transversely sectioned, 13 March 2005; 1 transversely sectioned, 15 April 2004. All type specimens mature and mated, from the type locality and same collectors as holotype Etymology. The species epithet chalonensis refers to the type locality, Chalone Creek. Other material. Mature or partially mature specimens from the type locality, sampled on various dates in February-March, 2004-2005, and used for measurement of morphological features: 34 whole-mounted, 7 dissected, and 2 histologically sectioned (1 transverse, 1 sagittal) (Table 1). All collected by S. V. Fend and P. G. Johnson, and deposited in USNM (1593386-1593439). Description. Segments 43–78. Length of fixed worms 10–23 mm; body diameter in X 0.30–0.60 mm. Proboscis 320−620 µm long, about 50 µm diameter at middle (Fig. 4A). Secondary annulus in anterior 1/4−1/3 of preclitellar segments, from IV to IX (Fig. 2A). All chaetae simple-pointed, sigmoid; in anterior segments increasing in length from II (60−84 µm) to VI or VII (101–141 µm); shorter in posterior segments (86−134 µm); nodulus distal (0.3 to 0.4 chaeta length from the tip), or about median in II; similar chaeta length in dorsal and ventral bundles (Fig. 2D). Male pores on the chaetal line, midway between chaetae and posterior septum (Fig. 3A, B); pores open on rounded porophores, i.e., outward folds of thin, non-clitellar epidermis, lined with a transverse-circular muscle layer continuous with circular muscles of body wall (Fig. 4C, D); porophores 30–55 μm high (depending on extension), 50–80 μm wide. One pair of simple spermathecal pores behind ventral chaetae in XI, on the ventral chaetal line, at about half the distance from ventral chaetae bundle to posterior septum, or slightly more posterior (Figs. 2A; 3A). Epidermis usually 6−10 µm thick in anterior segments, 10−20 µm in clitellum. Clitellum from chaetal line in IX or X to XII-XIII, with epidermal glands not strongly textured, organized in transverse rows (Fig. 4B). Pharynx mostly in II-III, thicker in III both dorsal and ventrally. Pharyngeal glands in IV−VII (a pair of ventral lobes may be present in VIII). Ventral blood vessel joins in IV. Nephridia absent in preclitellar segments; a short anteseptal funnel is followed by a thick, mostly postseptal granulated mass; a short ectal duct widens into a distinct vesicle (85–155 µm long by 22−55 µm in diameter) filled with a hematoxylin-staining substance, and terminating in a conspicuous nephridiopore (Figs. 3E; 4H), just anterior to ventral chaetae; posteriorly, there is a duct which may follow the ventral blood vessel into posterior segments. Sperm sacs extend anteriorly to VIII, posteriorly to XII−XVI; egg sacs to XIII−XVIII. Vasa deferentia 14−22 µm wide and both about the same length, 220−360 µm long. Posterior vas forms a loop in XI; both vasa join the muscle layer near the middle of atrium length and enter the lumen subapically. Atria club-shaped to somewhat petiolate with elongate ampulla, entirely in X (Figs. 3A, B; 4C), length 180–300 μm (0.4–0.7 times body diameter, 2.8–4.4 times porophore diameter), diameter in ampullar portion 40–80 μm, narrowing to 15–25 μm near the pore; atrial muscle layer thin (2–5 µm), and lumen 25−50 µm wide in most specimens. Prostate glands densely covering the ampulla, appearing diffuse in most specimens, but in some individuals forming small, dense, petiolate clusters of up to about 10 cells, 10−35 µm high. One pair of spermathecae in XI, distinctly petiolate with sac-like and elongate ampulla, may extend into XII. Sperm in the ampulla in loose, irregular bundles, not associated with epithelium (Fig. 4E, F). Short spermathecal ducts (43–90 µm long; 24–40 µm wide entally), tapered near the pore, with a thin muscle layer and columnar lining cells. Epidermis forming a low inward fold to 60 µm wide around pore, with a ring of about 8−10 short glands (30–60 µm high) (Figs. 3A, C, D; 4E, F); pore area surrounded by a distinct ring of muscle fibers in surface view (Figs. 3D; 4G). In partially mature or unmated specimens, the spermathecal ducts are similar to those in mature worms, but the ampullae are ovate and have a thick epithelium, becoming elongate with increasing maturity. Remarks. The structure of the spermathecae – an elongate (instead of nearly spherical) ampulla and a very short duct (Table 2) – with a ring of small glands surrounding the spermathecal pores distinguishes Eremidrilus chalonensis n. sp. from all other Eremidrilus species known so far. This species resembles other California species (E. elegans, E. coyote, E. ritocsi, and E. felini) in having club-shaped atria, male pores opening on broad, rounded porophores, and a single pair of spermathecae in the ovarian segment. The new species differs from previously described California species in the position of the spermathecal pores, which are in line with the ventral chaetae (Fig. 3C), instead of a slightly to strongly lateral position. One specimen has a single spermatheca in the usual position on one side, but only a small “bud” of cells in the other position. Dark detritus and a variety of diatoms are seen in the gut (Fig. 4I). Chalone Creek is a tributary to the Salinas River, a major central California river draining to Monterey Bay. Eremidrilus chalonensis was found in a mainstem reach of Chalone Creek, with highest numbers near the downstream boundary of Pinnacles National Park. In this area, the channel was relatively wide and alluvial, without a dense riparian corridor; the streambed has large gravel/cobble bars, and surface flow is intermittent, from approximately December through April (Bogan & Carlson 2018). The species was not found in more upstream reaches, where the channel is constrained by dense riparian trees (mostly Salix spp.), and the streambed is stabilized by tree roots. In addition to E. chalonensis, a more widespread congener, Eremidrilus felini Fend & Rodriguez 2003, was collected at the downstream site in Chalone Creek. At the type locality, immature specimens of E. chalonensis can be separated by the conspicuous, wide ectal vesicle in the nephridial duct. Two other Eremidrilus species (E. montanensis and E. gilita) have vesicles at the ectal end of the nephridial duct, but these are round and rather small in comparison (see Fend & Rodriguez 2020). Chalone Creek is also the type locality for the regionally endemic aquatic beetle, Optioservus canus Chandler, 1954 (Shepard 1990) (Coleoptera, Elmidae), the “Pinnacles riffle beetle”. Among aquatic oligochaetes, an undescribed species of Haplotaxidae collected from Chalone Creek may be regionally endemic (S. Fend, unpubl.).

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