Eremidrilus humboldti, Fend & Rodriguez, 2020

Fend, Steven & Rodriguez, Pilar, 2020, New Eremidrilus species (Clitellata: Lumbriculidae) from western North America Part 1, species with two spermathecal segments, Zootaxa 4809 (1), pp. 111-131 : 116-118

Eremidrilus humboldti n. sp.

( Figures 3 , 4 , 11C )

Holotype. USNM 1618760 . Whole worm, incomplete (tail segments missing), with sperm in anterior spermathecae, and mature egg, slide-mounted in Canada balsam.

Type Locality. USA, Idaho, Blaine Co., Corral Creek at Trail Creek , 1 Jun 2008 (Site 11, Table 1), coll. S. Fend.

Paratypes. MNCN 16.03 /3111, from the type locality ( Site 11), 1 Jun 2008, 1 whole-mount . USNM 1618762 Trail Creek at Trail Creek Road (Site 10), 30 Jun 2000, DG, 1 dissected . USNM 1618761 Site 10, 5 Sep 2004, DG, 1 whole-mount . USNM 1618763 , Corral Creek 1 km above Trail Creek (Site 12), 1 Jun 2016, PR and SF, 1 wholemount, DNA voucher (C. Erséus pers. com.) MNCN 16.03 /3112, Site 10, 5 Sep 2004, DG, 1 dissected. All slidemounted in Canada balsam .

Other material. From the type locality (Site 11), SF , 1 Jun 2008, 1 whole-mount and 1 dissected. Site 10, 5 Sep 2004, DG, 1 mature and 3 immature whole mounts; 15 Apr 2002, SF, 6 partially-mature whole mounts. Site 12, 1 Jun 2016, PR and SF, 3 whole-mounted DNA vouchers; 26 Sep 2019, SF, 3 whole mounts, all unmated. Site 13, 26 Sep 2019, SF, 8 whole mounts and 5 whole-mounted DNA vouchers. All slide-mounted in Canada balsam. Collectors: DG = Daniel L. Gustafson, PR = Pilar Rodriguez, SF = Steven Fend .

Etymology. Named for the great biologist and naturalist Alexander von Humboldt, who emphasized the relationships between species diversity and their distribution, forming the basis of biogeography, and inspiring many generations of zoologists and botanists.

Description. Length 12–26 mm; 54–74 segments; diameter in X 0.4–0.7 mm. Prostomium with proboscis, the latter 300–600 µm long, diameter about 80 µm at middle. Secondary segmentation well marked from IV–IX, weak in postclitellar segments ( Fig. 3A ). Chaetae moderately sigmoid, with nodulus slightly distal to midpoint (0.35–0.45 the distance from the tip); in anterior bundles 113–204 µm long, shorter in II, dorsals similar in length to ventrals; in mid body segments 120–216 µm long ( Fig. 3B ). Genital pores all on the longitudinal lines of ventral chaetae. Male pores on prominent dome-shaped porophores (26–84 µm high, 64–120 µm wide) in X, midway between chaetae and septum X/XI ( Figs. 3D,E , 4A ). Two pairs simple spermathecal pores in XI and XII; those in XI midway between chaetae and posterior septum; those in XII very close to posterior septum (12/13) ( Fig. 3 C–E). Female pores on 11/12.

Epidermis 9–24 µm thick in anterior segments, up to 40 µm in clitellum. Clitellum in X–XIII (XIV), not greatly thickened in most specimens. Pharyngeal glands in IV–VI (VII). First nephridium at 12/13 or 13/14; pores anterior to ventral chaetae, nephridial duct tubular at pore, without forming a vesicle.

Sperm sacs extend anteriorly to VIII or VII, posteriorly to XIII–XIX; egg sacs extend 1–2 segments beyond. Male funnels on 9/10 and 10/11. Vasa deferentia 18–24 µm diameter, about 250–400 µm long; posterior vasa loop into XI; both vasa join the atrium near mid-length and enter the muscle layer, opening to atrial lumen near the (ental) apical end ( Figs. 3 C–E, 4C). Atria short, 172–310 µm long, entirely in X, club-shaped, ampulla gradually narrows towards the pore, not clearly separated from the ectal duct; atrium length 0.3–0.5 times body width at segment X, and 2–3 times the porophore width ( Fig. 4A,B ). Maximum atrium diameter 38–69 µm; epithelial cells 5–10 µm thick; atrial muscle layer thin (3–6 µm); prostate glands 10–22 µm high, usually appearing as a continuous layer over most of the atrium, but in some specimens they can be seen as distinct clusters ( Fig. 4C ). No obvious glands at the ectal pore.

Spermathecal ampullae oval or sac-like, the first pair about 150–700 µm long, the second pair similar or slightly smaller, 170–480 µm long, sometimes without sperm ( Fig. 3D ). Spermathecal ducts 40–85 µm long, 25–35 µm maximum diameter, tapered to the pore ( Figs. 3 C–E; 4D–F); duct epithelium with columnar cells, usually with a gradual transition to the thinner epithelium of the ampulla ( Figs. 3E , 4E ).

Remarks. Eremidrilus humboldti n. sp. resembles the Pacific Coastal E. ritocsi Fend & Rodriguez, 2003 in the size of the atrium relative to the body diameter, and the male porophore is also similar. However, E. ritocsi has only one spermathecal segment, and the spermathecal pores are near the lateral line. Spermathecal morphology also differs: ampullae are more globular in E. ritocsi , with a characteristic sperm arrangement, and ducts are longer and more tubular ( Fend & Rodriguez 2003). As in other inland species described here, E. humboldti n. sp. has two spermathecal segments; spermathecae have short, tapered ducts, spermathecal pores are in line with ventral chaetal bundles, and the pores of the second pair are close to intersegment 12/13. It is distinguished from other species of the region by its small atrium ( Table 2) and by the broadly rounded male porophore, with a simple pore ( Fig. 4A ).

Figures

FIGURE 3. Eremidrilus humboldti n. sp. from Corral Creek (A, B, D, and Trail Creek (C, E). A. Anterior end, external view of an unmounted worm, showing position of genital pores. B. Two chaetal pairs; IX ventral (left) and XIV dorsal (right). C–E, reproductive organs in X–XII: C. Ventrolateral view of a mature worm; D. lateral view of a recently-mated worm, second spermatheca (in XII) without sperm; E. a slightly post-mature worm (mated, but sperm funnels without sperm; at a later stage than D).

FIGURE 4. Eremidrilus humboldti n. sp. from Corral Creek A. Porophore with male pore from a whole mount. B. Atrium photographed at different focal plane of the same preparation in A. C. Atrium showing apical junction of vas deferens. D. Spermatheca in XII, ampulla extending into XIII, from a whole mount. E. Spermatheca, showing ampulla and duct (insert, in a separate plane). F. Spermathecal duct, detail, from a whole mount.

FIGURE 11. Eremidrilus species having two spermathecal segments, schematic illustration comparing position and basic morphology of reproductive organs in X–XIII.