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

Trichodrilus baylesi sp. nov. (Figures 1, 2) Type locality: Oregon, Lane Co., Fall Creek, above Fall Creek reservoir, approximately N43.972, W122.541, gravel-cobble streambed near margins. Holotype: USNM 1740726: 10 May 2020, a whole mounted worm, thick epidermis of clitellum partially scraped off, stained with carmine and slide-mounted in Canada balsam. Paratypes: All from the type locality. USNM 1740727–1740730: 10 May 2020, 2 whole mounts, 1 sagittally sectioned. 17 April 2020, 1 dissected. CASIZ 242895–242899: 10 May 2020, 1 whole mount, 1 sagittally sectioned. 17 April 2020, 2 whole mounts. 19 March 2020, 1 dissected. MNCN 16.03 /579–16.03/581: 17 April 2020, 2 whole mounts. 10 May 2020, 1 dissected. All slide-mounted in Canada balsam. Other material examined: From the type locality. Mated specimens with mature eggs, unless otherwise noted. 19 March 2020: 1 dissected. 25 March 2220: 2 dissected, 1 whole mount. 17 April 2020: 6 whole mounts. 10 May 2020, 1 dissected, 1 whole mount. 9 April 2021, 2 unmated whole mounts. 20 April 2021, 3 whole mounts. Oregon, Lane Co., Fall Creek below Dolly Varden Campground, N43.9655, W122.6251, 20 April 2021, 3 whole mounts. Yamhill Co., seep along Little Deer Creek, a small stream draining west slope of Peavine Ridge, west of McMinnville, N45.2408, W123.3862, in mud and aquatic plants. 30 January 2000, 1 dissected (mated), 5 whole mounts (all unmated). Etymology: For David M. Bayles, in appreciation for his long career protecting rivers of the Pacific Northwest with the Pacific Rivers Council. Description (material from the type locality): Length of 3 complete specimens 24–41 mm, 71–78 segments; diameter of all specimens 0.55–0.84 mm in X, maximum diameter to 1.0 mm. Prostomium rounded-conical, about as long as wide (Fig. 1A). Secondary segmentation (a narrow anterior ring about ¼ length of segment) from V to IX or X, weak or lacking in posterior segments. Epidermis in anterior segments 8–20 µm thick, 8–16 µm in posterior segments. Chaetae paired, simple-pointed, sigmoid; length of dorsal chaetae in anterior segments and clitellar region slightly shorter than ventrals of the same segment, 110–195 µm; ventral chaetae 140–210 µm; nodulus 0.30–0.45 the chaeta length from tip in both dorsal and ventral bundles; within each pair, the inner chaeta (i.e., the one closer to the sagittal plane) is usually slightly longer, with more proximal nodulus; chaeta diameter 4–5 µm (Fig. 1B). Dorsal wall of pharynx moderately thickened in (I)II–III and ventrally in III, no distinct pharyngeal pad or pouch (Fig. 2A). Pharyngeal glands usually in III–IV or V (Fig. 1A). Chloragogen begins on gut in about VII. First nephridia usually paired on 6/7 (duct and nephridiopore in VII); second pair usually on 12/13 (in XIII); then occurring irregularly in posterior segments. Each nephridium with small anteseptal funnel (to 30 µm long), an elongate postseptal expansion (length about 80–120 µm, diameter to about 40 μm), and a long, highly convoluted duct loop that usually passes through 2 or 3 posterior segments ventral to the gut, widening slightly at a simple nephridiopore anterior to the ventral chaetae in the originating segment. Blood vessels obscure in most fixed specimens; where visible, one pair of simple, winding commissural vessels in anterior segments; no obvious lateral blood vessels in posterior segments; dorsal vessel closely appressed to gut in post-clitellar segments. Male pores in X, midway between chaetae and posterior septum, on ventral chaetal lines (Fig. 1A); within transverse openings when penes retracted, but penes at least partially everted in most fixed specimens (Figs. 1C, E, F; 2B–F). Female pores intersegmental on 11/12, each a lateral slit on or slightly lateral to the chaetal line; female funnels 150–250 µm high. Spermathecal pores behind ventral chaetae in XI (midway between chaetae and posterior septum), in inconspicuous transverse slits on the chaetal line (Fig. 2I). Clitellum distinctly glandular, from mid-IX or X (at 9/10) through XII or XIII, wholly surrounding the body (Fig. 2B); 20–46 µm thick. No obvious internal glands around genital pores. Testes small (not extending as far as chaetae) in IX and X; ovaries extend beyond mid-XI, usually to 11/12. Sperm sacs extend anteriad to VII or VIII and backward through XIII to XV; egg sacs extend 1–3 segments behind posterior sperm sacs. Spermathecal duct distinct, tubular, in two parts (Fig. 1C; 2I): the ectal part with a thick (15–25 µm), irregular epithelium and a muscle layer to 2 µm thick, length 120–240 μm, diameter gradually decreases from near ectal pore (40–100 µm) to junction with inner part. Ental part of duct 80–175 µm long, 50–80 µm in diameter (may be somewhat expanded medially), with columnar epithelium (Fig. 2I, J). Entally, the duct abruptly terminates in a narrow sphincter with muscular ring (Fig. 2J, K), before widening abruptly into the ampulla. Spermathecal ampulla sacciform, elongate (to over 1000 µm), usually extending back through 1–2 segments (to XII or XIII); maximum diameter 200–600 µm, filled with unordered sperm (Fig. 2L, M); epithelium 10–30 µm thick, but not columnar or vacuolated. Sperm loosely distributed throughout ampulla. One unmated specimen had an extra spermatheca on one side, in IX. Male funnels closely appressed to septa 9/10 and 10/11, both directed anteriad; funnels similar in size or posterior slightly larger, about 110–220 µm high (Fig. 1C, E, F). Anterior vasa deferentia length about 420–700 μm, width 21–24 µm, ciliated, winding through anterior X to septum 10/11. Posterior vasa deferentia length 350–630 µm, diameter 21–28 µm; from the funnel, they run down septum 10/11 and penetrate the posterior septum, forming a loop in XI before returning to X to join the atrial ampulla (Fig. 1C). Ental ends of both vasa deferentia penetrate the atrial muscle layer near the ectal 1/4–1/2 of the ampulla, run under the muscle, and enter the atrial lumen subapically (Fig. 1C, E, F; 2H). Atrium petiolate, ampulla ovate to nearly spherical (180–320 µm high, 120–270 µm wide) (Figs. 1E, F; 2E); epithelium and muscle layers each 5–10 µm thick; muscle fibers without a distinct pattern. Prostate glands densely cover the ampullar portion in multicellular bundles (Figs. 1E, F, 2G); prostate layer 60–120 µm thick, and may appear continuous when glands are densely packed. Atrial duct forms an irregular tube, the free portion (between base of penis and ampulla) 70–120 µm long, 40–70 µm wide near ampulla; ectal end tapering to 30 µm or less, and continuing within the penis (Figs. 1C, E, F; 2D–F). Conical penes 210–300 μm long, 80–100 μm wide at base when everted (Fig. 2C); to 170 μm long when retracted within deep, eversible folds (penial sacs); penis with outer epidermal layer about 5 µm thick, continuous with the sac lining, cuticle not thickened. Beneath the epidermis, a layer of circular muscles (ca. 4–8 µm thick) surrounds the tapered inner duct of the penis; longitudinal muscle fibers from inner wall of penis extend up to surround the duct (Figs. 1E; 2D–F). Penes appear to be extended by everting the sacs, and are possibly lengthened by contraction of circular muscles. Gut contents appear to be typical fine streambed detritus. Material from Little Deer Creek: The 6 specimens were near maturity, but unmated, without sperm in the spermathecae, and only 2 contained mature (yolky) eggs. General body size was similar to topotypic specimens (maximum body diameter 0.5–0.8 mm, anterior ventral chaetae 107–165 µm). General structure of the male ducts was similar, although generally smaller: ovate atrial ampulla 80–148 µm long, 58–117 µm wide; conical penes 80–125 µm long (Fig. 1D). These specimens were collected earlier in the year (January vs. April–May) than the topotypic worms, and the reproductive organs were apparently not as well developed. 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 ventrolateral in XI. Like other Trichodrilus species, T. baylesi sp. nov. is a relatively small, unpigmented worm. Using the key by Rodriguez & Giani (1994), Trichodrilus species with a single spermathecal segment, simple-pointed chaetae, and globularpetiolate atria having a moderately-developed muscle layer include the southeastern Nearctic Trichodrilus culveri and the central European Trichodrilus pragensis Vejdovský, 1876. Trichodrilus culveri differs in lacking any penial structure, and in having a very short, conical spermathecal duct (Cook 1975). The small penes (opening in a conical porophore and without a penial sac) of T. pragensis appear quite different from the large penes of the new species (see Table 1 below). The lateral blood vessels described in posterior segments of T. pragensis and several other species (Hrabĕ 1971) were also not seen in T. baylesi sp. nov., although this character may be difficult to define in preserved material (Rodriguez & Giani 1994). Unlike the new species, penes are not highly developed in most congeners. Two exceptions, T. longipenis Giani & Rodriguez, 1994 and T. leruthi Hrabĕ, 1937 (both of which have two spermathecal segments), have large, “ Type 2” penes, formed by extruding elongated lining cells of the atrial duct (Fig. 1F in Giani & Rodriguez 1994, Figs. 17D–G in Rodriguez & Giani 1994, Fig. 4 in Hrabě 1937). In contrast, T. baylesi sp. nov. has large penes within deep, eversible sacs; although clearly elongated when the sacs are everted, the penes are “ Type 1”, with epidermis surrounding internal musculature and duct (Fig. 17A, C in Rodriguez & Giani 1994). The sacs surrounding the retracted penes appear to be simple epidermal folds, thus differing from more histologically differentiated penial sacs described in other lumbriculid genera, e.g., Sylphella puccoon Rodriguez et al., 2014, or Eclipidrilus palustris (Smith, 1900). Among congene

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