Eclipidrilus daneus Cook, 1966

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 : 31-32

Eclipidrilus daneus Cook, 1966

MATERIAL EXAMINED: Louisiana: undetermined locality, 1.VI.1916, Paratypes, USNM 32908: the better material in 2 atrial dissections, 4 sagittally sectioned worms and 2 transversely sectioned. Mississippi: Hancock Co., Bay St. Louis, VI.1996. 1 mature, dissected; 3 whole mounts of immature specimens, from the R. Brinkhurst collection. South Carolina: Aiken Co., Savannah River Plant Site, Fourmile Branch, 13.III.2002, collected by J. Epler. 1 dissected. Montana: Swamp near Polson, 7.VII.1914, USNM 26301: 1 sagittal and 1 transversely sectioned worm.

Supplementary description

Pharynx thicker dorsally than ventrally. Usually two pairs of lateral blood vessels in segments behind XII, with many short branches posterior to XV. In the posterior half of the body, short branches have distended ends and appear to be associated with the body wall muscles. In middle segments, at least, one branch appears to join the perivisceral sinus, but others end in the coelom. Nephridia as described for E. pacificus (see above).

Male pores medial to chaetae, about halfway between chaetae and midventral line. Penes as described for E. palustris (see above); may be coiled within the penial sacs. In the Bay St. Louis specimen, the inner sacs of the penial structures are up to 1880 µm long; the protruded part of one penis extends an additional 1100 µm. Atrial ampulla with muscle wall 12–23 µm thick; a thin ental layer of circular muscle is surrounded by a thicker outer layer having muscle fibers arranged in an unopposed spiral, up to 50º from the longitudinal axis, but often nearly parallel in ectal part of ampulla. Atrial lumen 0.66–0.73 times total diameter of atrial muscle tube. Prostate glands may be large, to 180 µm long ( Brinkhurst [1998, Figure 4 E]). Vasa deferentia 11–26 µm thick, joining atria near ectal end of ampulla. Spermathecal pores about halfway between chaetae and midventral line. Spermathecal ducts terminate in a vestibule as described for E. palustris (see above).

Remarks

The distinction between this species and E. palustris is slight, and Cook (1971) suggested that future study might invalidate E. daneus . In the original daneus description, Cook (1966) stated that the two species differed mainly in thickness of the atrial musculature, and possibly as a consequence, in the degree of atrial curvature. E. palustris was distinguished as having an atrial lumen: total atrial diameter ratio of 0.3, as opposed to a ratio of 0.6–0.9 in E. daneus . Cook (1971) gave ranges of atrial muscle thickness from 60–100 µm in E. palustris , and 6–20 µm in E. daneus . Wassell (1984) confirmed these ranges after examining new material from several sites in Florida ( E. palustris ) and Louisiana ( E. daneus ), although values presented in Brinkhurst (1998) implied greater variation for E. daneus . Cook (1966) also described E. daneus as having thinner and less muscular penial structures than E. palustris , but this character also varied considerably within populations considered to be E. palustris . Brinkhurst (1998) suggested that some E. daneus specimens with thin or crumpled penial structures were in a post­reproductive state, implying that that some of the observed differences may relate to reproductive maturity of individual specimens. Two additional characters not emphasized in earlier descriptions may be of use in distinguishing these species. The internal, ventral pads of cells in X of E. palustris were not apparent in the E. daneus material (cf. Brinkhurst [1998, Fig. 4 A]). Prostate glands were generally larger in specimens identified as E. daneus , but there was considerable intraspecific variation in that character.

The new specimens from Florida and Alabama generally appeared closer to E. palustris than to E. daneus , consistent with prior distributional records. However, the atrial muscle thickness and lumen: atrium ratios were quite variable within populations, and were often intermediate between published values for the two species. One exceptional specimen from Rock Springs Run had thin­walled, folded atrial ampullae, resembling the description of E. daneus . Nevertheless, the small prostates and well­developed ventral pad of that specimen, plus its collection from a population of normal palustris , suggested that it was an aberrant E. palustris . As in the case of the penial structures, some of the variation in atrial morphology may be attributable to reproductive maturity. Additionally, the range in contraction of observed worm specimens implied variability in fixation methods. This sort of variation may also occur in other species. The lumen and tissue layers in the atrial ampulla varied either intraspecifically or with reproductive maturity in E. pacificus : ratios ranged from 0.1 to 0.6 in mated specimens from the type locality, and greater differences occurred among populations. As in the case of the E. pacificus variants, future collections from intermediate localities may determine whether differences among geographic forms of E. ( Premnodrilus ) represent distinctive species or clinal variation.

Figures

FIGURE 4. Reproductive segments of E. pacificus, typical specimens, Hoh River, Washington, reconstructed from transverse sections. A—male pore and atrial duct in X; arrows indicate lateral positions of midpoints of chaetal pairs. B—spermathecal pores and ducts in IX. Abbreviations: ad—atrial duct; ag—accessory gland; mf—male funnel; sa—spermathecal ampulla; sd—spermathecal duct; sv—spermathecal vestibule. Scale bar 200 µm.