Trichodrilus humptulips Fend & Rodriguez, 2024, sp. nov.

Trichodrilus humptulips sp. nov. (Figures 3, 4) Type locality: Washington, Grays Harbor Co. West Fork Humptulips River, near Campbell Tree Grove, N47.4812, W123.6831. Holotype: USNM 1740731: A whole mounted worm, stained with borax carmine, and slide-mounted in Canada balsam; collected 2 June 2003. Paratypes: USNM 1740732–1740734: From the type locality, 2 dissected, collected 2 June 2003; 1 whole mount, collected 29 April 2022. All slide-mounted in Canada balsam. Other material examined: From the type locality, 2 mature and 2 immature, collected 29 April 2022. Washington, Jefferson Co., Clearwater River at Upper Clearwater Camp, N47.6782, W124.1194, 4 June 2003; 1 partially mature worm. All whole-mounts in Canada balsam. Etymology: From the type locality; the name of the river apparently derived from an Indigenous language term meaning “hard to pole” (difficult to travel by canoe). Noun in apposition. Description: Length of preserved worms 23–31 mm; 81–90 segments; diameter 0.6–0.7 mm in X, maximum diameter to 0.75 mm. Prostomium short (0.18–0.24 mm) and rounded, slightly wider than long (Figs. 3A, 4A). Secondary segmentation (a narrow anterior ring, about ¼ length of segment) from IV–IX, weak or lacking in posterior segments (Fig. 3A). Chaetae paired, simple-pointed, sigmoid. Length of ventral chaetae in anterior segments and clitellar region 125–186 µm, dorsals similar or slightly shorter (114–176 µm) than corresponding ventrals; nodulus 0.36–0.42 the chaeta length from tip (Figs. 3B, 4C). Ventral chaetae slightly increase in length in middle and posterior segments (160–210 µm); nodulus more distal posterior to about XL (0.27–0.34 the chaeta length from tip). Within each pair, the inner chaeta may be slightly longer. Chaeta diameter 5–6 µm in anterior to middle segments; ventral chaetae in posterior segments somewhat thicker (6.5–9 µm). No distinct pharyngeal pad. Pharyngeal glands usually in IV–VI. No preclitellar nephridia; nephridia occurring irregularly in posterior segments; ducts thin, extending ventrally for 2 or more segments, without distinct ectal vesicle. Dorsal blood vessel on dorsal side of gut; lateral vessels are simple commissures in anterior segments, but no lateral blood vessels in posterior segments; ventral blood vessel with 2 or 3 short connections to perivisceral sinus. Chloragogen forming a relatively thin layer on gut, from VII. Male pores in X, midway between chaetae and posterior septum, on or slightly lateral to ventral chaetal line; pores surrounded by 120–145 µm wide ring of slightly thickened epidermis (cells 30–48 μm high); no obvious penis, porophore or sulcus (Fig. 4B, D). Female pores intersegmental on 11/12, inconspicuous, on the chaetal line. Female funnels 160–200 µm high. Spermathecal pores simple, inconspicuous (Fig. 4G), on ventral chaetal line and behind chaetae in XI (2/3 distance between chaetae and 11/12) and in XII (3/4 distance between chaetae and 12/13). Clitellum inconspicuous, from X–XIII. No obvious internal glands around genital pores. Testes to about mid-segment in IX and X; ovaries extend beyond mid-segment in XI. Sperm sacs extend anteriad to VIII and back to XV or XVI; egg sacs with mature eggs may extend up to 2 segments behind posterior sperm sacs. Spermathecal ducts distinct, 80–130 µm long, about 40–50 µm diameter near ampulla, tapering down to 25–30 µm at the pores (Fig. 3D); duct with narrowly columnar epithelium and narrow lumen. Spermathecal ampullae irregularly sacciform, about 500–1200 µm long, maximum diameter 180–280 µm; folded within originating segment or extending forward or back through 1–2 segments (Fig. 3D, E). Ampullar epithelium is nearly uniform (5–10 µm thick), not columnar or vacuolated (Fig. 4H). Sperm loosely distributed throughout ampulla. Male funnels closely appressed to septa 9/10 and 10/11, both directed anteriad; funnels similar in size or posterior slightly larger, to 200 µm high. Anterior vasa deferentia length about 420–560 μm; diameter 24–32 µm, winding through anterior X; posterior vasa deferentia length 560–720 µm, diameter 24–32 µm, forming an extensive loop in XI before returning to X to join the atrium basally (Fig. 3C–D) (medially in partially mature worm, Fig. 3F). Both vasa deferentia with ciliated lumen 8–10 µm wide; both join base of atrial ampulla, near beginning of prostate cells, where they abruptly narrow and penetrate muscle layer; internal ducts narrow (to 5–6 µm), continuing under atrial muscle coat and entering atrial lumen near apical ¼ or subapically (Fig. 3C, D). Atria club-shaped, total length 260–400 μm; indistinctly divided into a prostate-bearing ampulla (215–295 μm long, maximum diameter 50–90 μm) and an ectal section (40–130 μm long, 32–40 μm diameter) which tapers to 30 µm or less at pore. Atrial ampulla surrounded by a muscle layer 3–6 µm thick, muscle fibers without a distinct pattern; epithelium 14–24 µm thick (Fig. 4E, F). Multicellular prostate glands densely cover atrial ampulla; distinct, small cell bundles 20–40 µm high (Fig. 4F). Gut contents appear to be typical fine streambed detritus, mostly organic. The partially mature worm from the nearby Clearwater River has partially developed spermathecae in XI–XII, and atria in X (Fig. 3F). Remarks. The new species can be assigned to Trichodrilus based on the semiprosoporous male ducts, with testes in IX and X, atrium and male pore in X; ovaries in XI; and spermathecae in XI and XII. The type material is quite limited, but appears sufficient to reliably distinguish the new species from congeners. Of the previously described Trichodrilus species with two spermathecal segments, two Palearctic species, T. intermedius (Fauvel, 1903) and T. tacensis Hrabě, 1963, also have tubular atria which are shorter than the body diameter.Another species, T. leruthi Hrabĕ, 1937, has a tube-like, elongate atrium (Fig. 3 in Hrabě 1937), terminating in a prominent penial bulb, with extruded lining cells forming elongate penes (Fig. 5 in Rodriguez & Giani 1994). These 3 European species are known primarily from groundwater. Two main reproductive characters distinguish T. humptulips sp. nov. from T. tacensis: the posterior vasa deferentia of T. tacensis do not penetrate the posterior septum, and join the atrial ampulla at the apical end (see Fig. 6 in Hrabĕ 1963); T. tacensis also has well-developed, cylindrical penes on porophores. Using the key by Rodriguez & Giani (1994) (see Table 1), the closest match to the new species is T. intermedius, which also has posterior vasa deferentia penetrating the posterior septum (10/11), forming a loop in XI (Fig. 9 in Hrabě 1937). From the original description, T. intermedius differs in having 2–6 pairs of lateral blood vessels in posterior segments. Hrabě (1937) provided a detailed redescription, noting the very thick, muscular vasa deferentia (37–47 μm) and short-cylindrical penes. The muscle layer of the atrial ampulla in Hrabě's material appears somewhat thicker, at 9.5 μm, and both vasa deferentia join the atrial ampulla at the most ental (apical) end, in contrast to the basal junction of the new species.