Rhynchelmis aleutensis, Fend, 2005

Fend, Steven V., 2005, Rhynchelmis aleutensis n. sp. (Clitellata: Lumbriculidae) from Adak Island, Alaska, Zootaxa 1093 (1), pp. 45-53 : 46-50

Rhynchelmis aleutensis n. sp.

HOLOTYPE: USNM 1068555 , a dissected, slide­mounted specimen.

TYPE LOCALITY: ALASKA: Adak Island: Little Thumb Creek , VII.1995 .

PARATYPES: U.S. National Museum, Washington DC. USNM 1068556­1068558 : Adak Island: Finger Creek , 27.VI.1995, 2 sectioned worms (1 transverse, 1 sagittal), 3 dissected .

OTHER MATERIAL: Adak Island : Finger Creek, 27. VI.1995, 2 sectioned worms (1 transverse, 1 sagittal); 5 dissected, partially­mature specimens and several immature whole mounts.

ETYMOLOGY: refers to the type locality in the Aleutian Islands , Alaska .

DESCRIPTION: Length of preserved specimens 18–25 mm, width 0.9–1.0 mm in X; 75–92 segments. Prostomium with a distinct proboscis, about 0.5 mm long by 0.05 mm diameter. Segmentation moderately developed; each segment posterior to II usually has a weak secondary annulus at about the anterior 1/4. Clitellum from IX or X to XIII. Chaetae simple­pointed, sigmoid, with a moderate to strong distal hook; nodulus usually distal to midpoint, 35–45% of chaeta length from tip ( Fig. 1D ), but sometimes median in posterior segments. Chaeta length 226–274 m in middle and posterior segments, dorsal chaetae may be slightly shorter than ventrals. Paired spermathecal openings on ventral chaetal lines, about midway between ventral chaetae and posterior septum in VIII. Ventrolateral margins of VIII may be expanded into blunt lobes, possibly claspers ( Figs. 1A–C, 1E ). Male pores on ventral chaetal line, posterior to the chaetae in X, within short, raised rings of thickened epidermis ( Figs. 1A–C, 1F , 2A ). Female pores indistinct at 11/12, on ventral chaetal line.

Epidermis 14–17 m thick anteriorly, 20–50 m thick in clitellum. Longitudinal muscle layer of body wall 40–50 m thick in preclitellar segments; circular muscle layer 6–8 m. Longitudinal muscles divided at chaetal and lateral lines into bands which do not curl strongly inward at the edges ( Figs. 1E–F ). Brain in the peristomium; major ventral nerves join in II. Pharynx in II–V, dorsal and ventral walls about equally thickened. Pharyngeal glands from IV to VI.

Ventral blood vessel divides in VII, branches connect to dorsal vessel in preclitellar segments via one pair of convoluted commissural vessels. No obvious lateral blood vessels posterior to X in the available material. Nephridia usually begin in XIII, paired, single, or absent in posterior segments. A small anteseptal funnel is followed by an irregular postseptal mass; a dorsal tubule loop approaches the dorsal blood vessel, a short tubule goes to an inconspicuous nephropore anterior to the ventral chaetal bundle, and another tubule may extend posteriorly into other segments.

Testes paired in X, ovaries paired in XI. Female funnels prominent at 11/12, pores intersegmental. Sperm sacs to as far as XVII in mature worms, egg sacs to as far as XXII. Vestigial sperm sacs usually paired, extending posteriorly from 8/9 and 9/10. Spermathecae paired in VIII, each pore may be surrounded by a broad, indistinctly raised area of slightly thickened epidermis; internally, pores may be surrounded by weakly developed accessory glands (not visible on most specimens). Spermathecae fusiform, 330– 600 m long, with about the middle third widened into an indistinct ampulla; entally, the ampulla narrows before it communicates with the gut ( Fig. 1E ). One pair of unbranched diverticula joins ampulla near ectal end, on medial and lateral sides. Spermathecal diverticula tubular, 200–500 m long by 40–50 m in diameter; ental ends may be slightly expanded to about 60 m. Ectal duct and ampulla of spermatheca with outer muscle layer 5–10 m thick; muscle layer of diverticula 3– 4 m. Ectal duct 100–150 m long, 50–60 m wide at ampulla, but narrowed ectally, lined with columnar cells. Spermathecal sperm loosely arranged, but usually concentrated in ental ends of diverticula, with heads lined up along epithelium. Spermathecal ampulla, duct, and short diverticula develop before the ampulla joins the gut in partially mature specimens.

Male pores on low, rounded­conical “penes” within shallow concavities surrounded by raised rings; the entire structure is an infolded pad of thickened epidermal cells ( Fig. 1F ). Retracted penis to 130–220 m wide by 60–140 m tall; the entire pad is 250–430 m in diameter (but probably varies with contraction). Epidermal cells of pad and penis are elongate, with elongate nuclei; fibrous cell extensions form a dense ectal layer ( Fig. 2A ). Unlike the surrounding clitellum, epidermal cells of pad do not appear to be glandular. Entally, the concave pad is surrounded by a thin layer of loose, somewhat granular cells, which sometimes appear as small, petiolate clumps, but may be interspersed with the epidermal cells in the penis ( Fig. 2A ). Atria tubular, 2200 to 5000 m long, usually contorted, extending as far as XV ( Fig. 1G ). Atrial diameter 50–100 m in ectal part, with muscle coat 2–5 m, and normal cuboidal epithelium ( Fig. 2B ). Ental 1/4 to 1/2 of atrium 50–110 m in diameter, muscle layer 4–10 m thick, covered with petiolate, multicellular prostate glands ( Figs. 2C–D ). Prostate glands 50 to 80 m long, highly granular, without distinct cell boundaries; narrow ends penetrate atrial muscle, forming clusters of extensions containing granular vacuoles among the atrial epithelial cells. Anterior male funnels cup­shaped, to 180 m high, without sperm. Vasa deferentia ciliated, diameter usually 30–50 m ( Fig. 2B ); anterior vas non­functional, but similar in size to or slightly narrower than the posterior. Both vasa deferentia join the atrial muscle coat near the middle of the prostate­covered portion or near the ental end; vasa travel under the muscle coat a short distance to enter the lumen slightly before the ental end ( Fig. 2C ). Posterior male funnel with sperm; highly convoluted, 200 to 340 m in diameter, on 9/10. Posterior vas deferens enters X directly, without forming a loop into XI.

REMARKS: The two spermathecal diverticula, the modified male pores, the nonfunctional anterior vasa deferentia, and the tubular atria, having prostate bundles restricted to the ental part, appear to associate the new species with the “ Sutroa ” group of Nearctic species (equivalent to “Group 1” in Fend and Brinkhurst 2000; note that the group is no longer defined by a single median spermatheca). However, differences in morphological details suggests that R. aleutensis is distantly related to the more southern species. The structures surrounding the male pores could be interpreted as intermediate between the thick pads of R. brooksi Holmquist, 1976 and the distinctly invaginated, eversible penial bulbs of the Sutroa group (cf. Fend & Brinkhurst 2000: Figs. 77 vs. 22– 23). The structures may be eversible, although none was seen in an everted state, and distinct retractor muscles were not evident. Histologically, they appear as folded, thickened epidermis, rather than the mix of muscular and glandular cells seen in Sutroa group penial bulbs. Unfortunately, the poor histological condition of the available specimens limits the comparison.

Within the Sutroa group, R. aleutensis most closely resembles Rhynchelmis gilensis Fend & Brinkhurst, 2000 . Like R. gilensis , and in contrast to most Sutroa group species, the atrial muscle layer is not thickened in the ectal part, and both vasa deferentia enter the atria near the ental end. The paired spermathecae resemble the single, median spermatheca of R. gilensis , but lack the ectal “bulb” (cf. Fend & Brinkhurst 2000: Figs. 6, 46) and anterior pore position common to R. gilensis and all other species in the Sutroa group. The two spermathecal diverticula join the base of the ampulla, rather than the junction between the ectal duct and the ampulla.

The vasa deferentia are thicker than in any of the Nearctic Rhynchelmis s. lat. species, but do not appear to be glandular, or remarkably thickened (nearly as thick as the atria), as in the Palearctic Rhynchelmis s. str. (cf. Hrab 1982). Atria with prostate glands restricted to a relatively short portion of the atrium are also characteristic of Rhynchelmis brooksi and Rhynchelmis malevici (Sokolskaya 1983) , but those species have only a single vas deferens per atrium, and the middle portion of the atrium is histologically modified.

Rhynchelmis species typically have branched lateral blood vessels posterior to about VIII–X ( Cook 1971). The apparent lack of lateral blood vessels in R. aleutensis may be an artifact of poor fixation, but blood­vascular systems appear to be reduced within closely related Rhynchelmis species groups (e.g. Rhynchelmis alaskana Holmquist, 1976 vs. Rhynchelmis saxosa Fend & Brinkhurst, 2000 ). The nephridia resemble other Rhynchelmis in having a postseptal duct loop that approaches the dorsal blood vessel ( Fend & Brinkhurst 2000).

Figures

FIGURE 1. R. aleutensis n. sp. (A–C) Ventral, ventrolateral, and lateral views of genital segments of whole worm, showing pores and claspers. The specimen was highly contracted, somewhat obscuring the secondary annulation. (D) Chaetae, from left to right: two ventral chaetae (segments VIII and XX) from a Finger Creek specimen, two ventral chaetae (VI and XII) and a pair (XXX) from a Little Thumb Creek specimen. (E–F) Transverse views of VIII, showing spermathecae joining the gut; and X, showing male pores and ectal part of atria; reconstructed from sections. No accessory glands were visible at the spermathecal pores of this specimen. (G) Sagittal view of atrium, from a dissection. Arrow indicates beginning of prostate glands (glands omitted in part for clarity). One of the vasa deferentia is embedded in the atrial muscle near the ental end; the other could not be followed in this specimen. Scale bars 100 m (D), 400 m (E–F).

FIGURE 2. R. aleutensis n. sp. (A) Transverse section of male pore. (B) Transverse section of ectal part of atrium, with vasa deferentia. (C) Transverse section of ental part of atrium, with one vas deferens approaching the atrium, and the other within the atrial muscle coat. A prostate gland extends through the muscle coat, with granular vacuoles displacing the epithelial cells. (D) Sagittal section of the ental part of the atrium.