Dicelis eudrilii, Ivanova, Elena S. & Hope, Duane, 2009

Ivanova, Elena S. & Hope, Duane, 2009, A new genus and three new species of Drilonematidae (Rhabditida, Drilonematoidea) from earthworms, Zootaxa 2293, pp. 53-67 : 54-58

Dicelis eudrilii n. sp.

( Figs 1–2 )

Measurements: Table 1.

TABLE 1. Morphometrics of Dicelis eudrilii n. gen., n. sp. Measurements are ranges in µm.

Adult: Large drilonematids. Body long, cylindrical, barely tapering to anterior end, with short conoid tail in both sexes. Cuticle finely striated. Lateral chords about 13–18 µm wide, comprised of two rows of vacuolated cells. Head bluntly rounded, bearing two circles of small cephalic papillae (6+4). Mouth aperture terminal. Stoma short, infundibular. Amphidial apertures not discernible, short bundle of sensilla conspicuous posterior to head papillae. Pharynx short, cylindroid and heavily muscled: cardia short. Nerve ring surrounding constriction of intestine about 2–3 body diameters posterior to pharynx base. Excretory pore about 2 µm in diameter, 1 body diameter posterior to nerve ring. Excretory duct as wide as excretory pore, about 13–22 µm long and cuticularised; excretory cell enormous. Intestine well-developed, thick-walled. Tail bearing small fimbriate caudal organs situated slightly asymmetrically near mid-tail length.

Male: Body about 2.6–3.4 mm long. Stoma 2–5 µm long and 7–10 µm in diameter. Pharynx 22–25 µm in diameter. Testis long, reflexed slightly posterior to excretory pore. Distal end of testis flexure 220–570 µm long. Immature sperm spherical, about 5–6 µm in diameter. Spermatids in ejaculatory duct about 17–20 µm x 14–18 µm in size. Copulatory muscles prominent. Spicules long, distinctly cephalate, heavily sclerotized, uniformly curved and bearing paired, serrated ventrolateral ridges; capitula about 1/7 of length, slightly elongated, and similar in diameter to shaft; distal tips long, thin, rounded. Gubernaculum about 1/2 of spicule length, plate-like, sometimes with short proximal process bent posteriad. Paired, prominent precloacal papillae present in front of cloaca and a pair of smaller ones just posterior to cloaca, both subventrally placed and covered by very thin membrane. Fimbriate caudal organs slightly raised, with a circular aperture 6–9 µm in diameter and convex radially striated rim 10–12 µm in diameter, located just anterior of mid-tail length. Tail well-tapered, tail tip rounded.

Female: Body about 4–5.3 mm long. Stoma 7–10 µm long and 8–15 µm in diameter. Pharynx 30–32 µm in diameter. Proximal tip of ovary situated between vulva and anus; ovary looped twice between distal and proximal ends of ovary; oviduct flexed posteriorly at junction with about 3 pharynx lengths from anterior. Spermatheca, 240–275 µm long, directed anteriorly from flexed juncture of ovary and oviduct and filled with large bean-like spermatozoa 8–14 µm x 4–6 µm in size. Oviduct looped and bearing spherical cells (of glandular nature?). Uterus large, thin-walled, packed with numerous eggs. Eggs widely elliptical, shell about 1.5 µm thick, covered by irregularly shaped, flat, densely packed minute tubercles. Vagina straight, short. Vulval lips not prominent. Vulva post-median. No post-uterine sac present. Rectum long with sclerotized lining. Rectal glands present. Tail slightly larger in diameter than in males, tapering to the end with blunt conical tip 2–3 µm long. Fimbriate organs situated at mid-tail or slightly further back; the same in structure as in males, 17–25 µm in diameter of outer rim, aperture 8–15 µm in diameter. Three caudal glands present.

Juvenile. Head end, pharynx, nerve ring and excretory pore as in adult nematodes. L III: vulval primordium situated at posterior end of genital primordium measuring 620 µm long.

Type material: Holotype female USNM 1117733, paratype female USNM 1117734, 2 paratype males USNM 1117735 and 1117736, immature female USNM 1117737 and juvenile USNM 1117738 deposited in the Smithsonian Institution’s National Museum of Natural History. Further paratype female No 1068 deposited in the Museum of Helminthological Collections in the Centre of Parasitology of A.N. Severtsov Institute of Ecology and Evolution RAS, Moscow, Russia and paratype male and fragments of male and female are in the first author’s collection.

Type host and locality: Coelomic cavity of Eudrilus sp., USNM 52754, collected 145 miles NW from Lagos, University of Ifa, Nigeria, May–June 1975, leg. A.O. Segun.

Etymology: The species is named after its earthworm host.

Diagnosis and relationships. Drilonematoidea, Drilonematidae, Dicelinae. This species is characterized by well-tapered, conoid tail in both sexes, cephalic papillae in two circles, cylindroid pharynx, faint amphids with pore-like apertures, conspicuous excretory pore, nerve ring situated around intestine in front of excretory pore in adults and juveniles, long off-set spermatheca, post-median position of vulva, lack of post-uterine sac, smallish fimbriate organs, strong long spicules, and male caudal papillae reduced to two pairs.

A narrowly conoid tail, prominent excretory pore, very long spermatheca, relatively long spicules and presence of only two pairs of male caudal papillae distinguish this species from the other nominal species in the genus, all of them of Palearctic origin and parasitic in lumbricid earthworms. The genus Dicelis includes 14 species, viz. D. filaria Dujardin, 1845 (type species), D. caledoniensis Spiridonov, Ivanova & Wilson, 2005 , D. eiseniae Timm, 1967 , D. hyrcanus Belostotskaya, Kozodoi & Spiridonov, 1987 , D. keimeri Morand, Ivanova & Vaucher, 1996 , D. kimmeriensis Ivanova, 1993 , D. lovatiana Ivanova, 1993 , D. lumbricicola Ivanova, 1993 , D. nira Chitwood & Lucker, 1934 , D. pereliae Ivanova, 1993 , D. rossica Timm, 1967 , D. rubidi Ivanova, 1994 , D. sibirica Ivanova, 1994 and D. ussuriensis Spiridonov, Ivanova & Wilson, 2005 . All of them have shorter, broader, cylindroid or conoid tails, often with digitiform appendages, much smaller and sometimes morphologically indistinct spermatheca, shorter spicules and indistinct excretory pore and duct. Exceptional for, and characteristic of, D. eiseniae , are the position of the vulva near mid-body and the presence of a post-uterine sac.

The characters by which this species differs from other species of Dicelis , namely the narrowly conoid tail, prominent excretory pore, very long spermatheca and spicules, post-median vulva position and fimbriate organs, are more similar to characters of another genus of the same subfamily, namely Adieronema Timm, 1967 . This latter genus is parasitic in megascolecid earthworms of East-Asian origin, but Dicelis differs from this genus by the absence of polar differentiation in eggs, (present in Adieronema ).

Remarks. The Dicelinae, to which this species is assigned, contains only two genera, Dicelis and Adieronema . The first is parasitic in lumbricid earthworms and the second in megascolecids. Our new species is the first representative of the subfamily parasitic in a host from another family and geographical region.

Timm (1967) differentiated Adieronema from Dicelis on the basis of a few characters, i.e. larger size, prominent excretory pore and very numerous typical ova with bipolar corona. This species displays affinities with species of both genera. In terms of general appearance it more strongly resembles species of Adieronema than those of Dicelis , but shares similarities with Dicelis spp. in body size, and less numerous (several dozens vs several hundreds), but larger sized eggs lacking polar differentiation. For several species of Dicelis ( D. hyrcanus , D. lovatiana , D. rubidi , D. caledoniensis ) it has been shown that the nerve ring in juveniles is situated around the pharynx, but that it “slips” to a position around the intestine during the growth of the nematodes. In the new species the nerve ring position remains the same in both adults and juveniles.

This species may represent yet another lineage of the genus, associated with eudrilid earthworms.

Paradicelis gen. n.

Diagnosis. Drilonematoidea, Drilonematidae, Dicelinae. Four papilliform cephalic sensilla. Mouth aperture terminal. Stoma short, infundibular. Amphids pore-like. Pharynx cylindroid. Nerve ring circum-intestinal. Excretory pore anterior to nerve ring. Males monorchic; spicules paired and curved; gubernaculum plate-like. Irregular bursa supported by whip-like sensilla. Paired small caudal fimbriate organs present. Females unknown.

Etymology: The generic name reflects an affinity with the genus Dicelis .

Type and only species: Paradicelis bursata gen. n., sp. n.

Figures

FIGURE 1. Dicelis eudrilii sp. n. A – D male; A: entire view; B: tail; C: spicule and gubernaculum; D: head; E – G: juvenile; E: head; F: pharyngeal region; G: vulval primordium. All in lateral position. (Scale bars in µm.)

FIGURE 2. Dicelis eudrilii sp. n. female. A: entire view; B: pharyngeal region; C: excretory pore; D: egg; E: spermatheca; F: tail, ventral view; G: tail; H: caudal fimbriate organs, ventral view; I: fimbriate organs. If not indicated, in lateral position. (Scale bars in µm.)