Eclipidrilus lacustris (Verrill)

Steven & Fend, V., 2005, A review of the genus Eclipidrilus (Annelida: Clitellata: Lumbriculidae), with description of a new species from western North America, Zootaxa 969, pp. 1-42 : 22-25

Eclipidrilus lacustris (Verrill) ( Figures 13–14 )

MATERIAL EXAMINED: Canada: Ontario: Lake Superior, Saint Ignace Island, south side, 1871. USNM 17947, paralectotypes: 3 whole mounted worms on one slide, labeled O­104; 2 sagittally sectioned worms, series labeled O­12 and O­480; 1 transversely sectioned, series labeled O­11. United Kingdom: Wales: Bala Lake, collected by D. Cook, R. Brinkhurst collection. 2 longitudinally sectioned worms (1 sagittal, 1 horizontal). USA: Montana: Granite Co.: Ranch Creek, 22.VI.1997. 1 dissected. Missoula Co.: Bitterroot River at Maclay Flats, 46º50’16”N, 114º06’01”W, 11.XI.2001. 1 mature and 2 partially mature, dissected. Clearwater River below Seeley Lake, 47º10’13”N, 113º28’50”W, 12.IV.1997. 2 dissected, partially mature. Swan River, 47º25’24”N, 113º40’05”W, 26.VI.1999. 2 whole mounts, 9 dissected, 1 sagittally sectioned, 1 transversely sectioned. Ravalli Co.: North Burnt Fork Creek, 46º31’09”N, 114º03’49”W, 10.III.1997. 1 dissected. All Montana specimens collected by D. L. Gustafson. Oregon: Jackson Co: Rogue River near Grants Pass, 42º24’45”N, 123º07’36”W, collected by S. Fend, 1.VI.2003. 7 dissected. Rogue River at Gold Hill, 42º25’50”N, 123º02’45”W, collected by S. Fend, 28.IV.2004. 5 whole mounts.

Supplementary description

Pharynx thickened dorsally from middle of I and ventrally from mid­II or 2/3; ventral wall nearly as thick as dorsal ( Fig. 14 B). One pair of long, convoluted commissural blood vessels in preclitellar segments; their insertion in the ventral vessel usually 1 segment posterior to insertion in the dorsal vessel. Anterior end of each segment from XIII to about XX or XXII with one pair of thick, lateral blood vessels which join perivisceral sinus at lower side of gut; these vessels usually unbranched or with few short branches. Posterior segments usually have two pairs of thinner lateral vessels, with numerous, short, blind branches or caecae in at least the posterior 1/2 of the body. Nephridial arrangement and morphology as described for E. pacificus (see above).

Testes in IX smaller than those in X. Sperm sacs and male funnels without mature sperm, but some apparent morulae may be present in both anterior and posterior sacs. Mature eggs present. Anterior male funnels small but ciliated and convoluted; posterior funnel much larger and highly convoluted. Vasa deferentia 10–17 µm in diameter. Male pore within a short (40–100 µm tall by 115–140 µm wide) collar of elongate epidermal cells; a small papilla may be present, but most specimens without penes or other duct modifications ( Fig. 13 C). Collar may be retracted into the body, forming a shallow pit. Cells of collar interspersed with ducts from petiolate accessory glands. Ectal duct of atrium mostly cylindrical, but tapered in the ectal 1/3; a thin layer of muscle with nearly transverse fibers in opposing spirals is surrounded by loosely­packed longitudinal muscle. Epithelial cells of the ectal duct are cuboidal to somewhat columnar.

Musculature of atrial ampulla in 2 main layers ( Fig. 13 A–B). Outer layer 4–11 µm thick; fibers arranged longitudinally (parallel to long axis of atrium). Inner layer 32–80 µm thick; fibers arranged diagonally in opposing spirals at a 60–70º angle from the longitudinal axis ( Fig. 13 A), but may be nearly transverse in innermost part. In sagittal sections the inner layer appears as many thin (2–3 µm thick) lamellae having alternating orientation, but in surface view they appear as a crosshatched pattern ( Fig. 13 A). Atrial epithelium very thin and often indistinct. Lumen of ampulla 90–180 µm wide, or 0.4–0.7 times atrium diameter. Prostate glands petiolate, usually numerous over entire atrial ampulla ( Fig. 13 B); 50–90 µm tall in Montana specimens, to 120 µm in Oregon specimens, and over 200 µm in some Lake Superior and Lake Bala specimens.

Spermathecal duct cylindrical, terminating abruptly in a narrow sphincter of transverse­circular muscle ( Fig. 13 D). Spermathecal pore midventral, slightly behind chaetae in IX, within a small pad of slightly thickened epidermis, surrounded by a cluster of petiolate accessory glands. Spermathecal ampulla ovate to pear­shaped with narrowed ental end. Ampulla has thin (12 µm), cuboidal epithelium in about the ectal 1/3; an amorphous mass of undetermined material is contained within this portion ( Fig. 13 E). Epithelium in the ental 2/3 with thick (30–50 µm), vacuolated cells. Vacuoles contain substance staining with eosin Y in the Montana specimens, and with an unknown stain in the Lake Superior and Lake Bala specimens. One Lake Superior specimen has a second spermatheca with the pore in the anterior half of IX.

Remarks

All specimens of this widely distributed species were morphologically similar. The Lake Superior specimens are from the series described by Smith (1919) and redescribed by Brinkhurst (1998); material from Lake Bala (presumably introduced) was apparently from a series described by Cook (1967).

The blood vessels, pharyngeal glands, atrial musculature and vasa deferentia of the new material correspond to earlier descriptions by Smith (1919) and Cook (1967). Cook described the prostate glands as a “diffuse layer”, but the present material has distinct prostatic cell bundles. Cook also described (without illustration) a “small, protrusible” penis. Brinkhurst (1998, Fig. 5 B,E) described and illustrated a small papilla within a shallow penial sac, surrounded by “lips” (= the “collar” in the present account), and implied that the end of the atrial duct may be protrusible. The new material generally resembles the latter description, but there is no evidence of a distinct penis: most specimens lacked an ectal papilla, and neither duct nor lining cells was extruded in any of the specimens. The ectal duct extends vertically within the body, with no evidence of a stiffening or retracting structure, and the lining is not detached from the muscle layer.

Many specimens had well­developed testes, ovaries, and clitellum, and mature eggs within the egg sacs, but neither the new material nor the museum specimens had mature sperm in sperm sacs, on male funnels, or in spermathecae. The amorphous contents of the spermathecal ampullae and the darkly staining material in the epithelial cells suggest a secretory function (M. Ferraguti, personal communication). It is unlikely that all individuals were at a post­mature state on the multiple sampling dates; consequently, it appears that the examined populations are parthenogenetic. As this condition was not reported in previous descriptions, this may not be the general case for the species.

Figures

FIGURE 5. Male ducts of typical E. pacificus from the Hoh River, Washington, from dissections. A—atrial ampulla. B—ectal half of atrial duct showing transition from cuboidal epithelial cells to fibrous lining of penial structure. C—ectal end of atrial duct with columnar epithelial cells, from a partially mature worm. D—penis with fibrous, extruded epithelial cells, from a mature worm. Abbreviations: ep—epithelium; lm—longitudinal muscle; pr—prostate gland; tm—transverse­circular muscle. Scale bars 200 µm (A – B), 100 µm (C – D).

FIGURE 13. Eclipidrilus lacustris, from Swan River, Montana (A­E); E. ithys, from Spicket River, Massachusetts (F). A—muscle layers of atrial ampulla, sagittal section: fibers of inner, transversediagonal layer appear crosshatched in center, and as alternating layers in sagittally sectioned wall; thin outer layer has longitudinal fibers. B—transverse section of atrial ampulla and prostate glands; a vas deferens is embedded between the thin longitudinal muscle layer and the thick inner layer. C—male pore, showing ectal end of atrial duct and the collar of thickened epidermis; from a transverse section. D—spermathecal pore, showing end of duct with narrow, terminal sphincter, sagittal section. E—spermathecal ampulla and part of duct; thin­walled ectal part of ampulla is to the left, thick­walled ental part to the right; sagittal section. F—ectal part of atrial duct, showing undifferentiated lining cells. Abbreviations: ag—accessory gland; ep—epithelium; lm—longitudinal muscle; muPmuscle; sa—spermathecal ampulla; sd—spermathecal duct; sp—spermathecal pore; tmtransverse­diagonal muscle. Scale bars 50 µm.

FIGURE 14. Head and pharynx of Eclipidrilus species; sagittal sections. A— E. pacificus, from Peavine Ridge, Oregon, showing the thin ventral wall of the pharynx. B— E. lacustris, from the Swan River, Montana; the pharynx is nearly as thick ventrally as dorsally.