Dolichorhabditis tereticorpus Kito & Ohyama, 2008, sp. n.

Dolichorhabditis tereticorpus sp. n.

(Fig.2, 3)

Type specimens. Eight females. Holotype ZIHU 3317 and paratypes ZIHU 3318-3324, deposited in collections of the Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan. Collected by K. Kito on February 8, 1996.

Type locality and habitat. Rocky coast facing Shannon Bay near Casey Station (66o17’S, 110 o32’E), Bailey Peninsula, Budd Coast of Wilkes Land, East Antarctica [Sector 2 of Andrássy (1998)]. Sediment contaminated with the treated effluent disposed from the station.

Measurements. Table 1.

Characters: a,b,c, de Man's ratios; V, position of vulva as a percentage of the body length from anterior end.

Description. FEMALE (Holotype ZIHU 3317: range and/or avg±sd for 8 specimens in parentheses). Body (Fig. 2 -A) almost cylindrical, gradually tapering to anterior end, abruptly tapering from level of anus to tail end. Maximum body diameter near or at level of vulva. Cuticle 0.6-0.9 μm thick, transversely striated, annules 0.8 (0.8–1.1) µm wide at midbody. Lateral field with four longitudinal lines (three ridges), but often inconspicuous (Fig. 2 F, G); 2.3–5.6 µm wide or about 8–16 % of body diameter at level of vulva in paratypes.

Head (Fig. 2 C) truncate, not offset or weakly offset; six lips slightly protuberant, equipped with 6+4 papilliform sensilla. Amphid aperture small, oval-shaped, located on lateral lips. Stoma nearly cylindrical, 1.9 (1.9– 2.7, 2.2±0.3) lip region diameters or 3.8 (3.7–4.9, 4.1±0.4) stoma diameters in length; cheilostom unsclerotized, promesostom cylindrical, well cuticularized and slightly tapering anteriorly; glottoid apparatus isomorphic, metastom with two tooth-like denticles. Pharyngeal collar extending to middle of stoma, about 0.6 (0.5– 0.6) stoma lengths. Corpus of pharynx (Fig. 2 B) almost cylindrical without a median bulb or swelling, junction with isthmus marked by expansion of triradiate lumenal rays and transverse slit of muscular wall (Fig. 3 A), 54 (53–57, 54±1.6) % of pharynx length, maximum diameter 14 (10–15, 13±1.7) µm or 61 (50–65, 57±0.05) % of corresponding body diameter. Terminal bulb with duplex haustrulum, 31 (26–33, 30±2.4) µm long by 21 (18–23, 21±1.8) µm wide. Nerve ring surrounding middle of isthmus, 67 (54–73, 64±5.5) % of pharynx length from anterior end. Excretory pore (Fig. 2 D) 83 (52–91, 75+11) % of pharynx length from anterior end; duct conspicuously cuticularized. Hemizonid not observed. Deirids conspicuous in lateral field posterior to nerve ring, located at 77 (59–77, 71±7.7) % of pharynx length from anterior end.

Reproductive system (Fig. 2 E) amphidelphic. Ovaries homodromous, reflexed dorsally at 26 (18–29, 25±3.9) % and 23 (17–27, 22±3.9) % of body length anterior and posterior to vulva, respectively; anterior ovary located on right side of intestine and posterior on left side; dorsal flexures extending to level of oviduct. Two pseudocoelomocytes located before flexure of anterior ovary, one behind flexure of posterior ovary (0–2 pseudocoelomocytes observed in paratypes). Oviduct short, cell arrangement inconspicuous; spermatheca located at dorsal side of oviduct and connected to its distal portion (Fig. 3 B); spermatheca rounded in young female. Uteri containing eight (0–12) eggs in various embryonic stages. Vulva (Fig. 2 G) transversely slit-like, located near midbody; vulval region slightly protruding ventrally. Vagina weakly cuticularized, 5 (5–10; 8±1.7) μm long or 15 (15–35, 28±7.7) % of vulval body diameter. Rectum (Fig. 2 H, 3C, D) extremely long and proximally expanded, 2.8 (2.6–4.7, 3.2±0.7) abd; three large rectal glands conspicuous, each followed by a few small cells.

Tail conical, with pointed tip end, 4.6 (4.2–7.9, 5.3±1.1) abd or 1.7 (1.5–2.1, 1.7±0.2) rectum length. Phasmids distinct, about 1.4 (1.0–1.8, 1.3±0.3) abd or 31(22–31, 25±3.6) % of tail length from level of anus.

MALE. Unknown.

Etymology. The specific name tereticorpus refers to the pharyngeal corpus which is almost cylindrical without swelling.

Diagnosis and relationships. Dolichorhabditis tereticorpus sp. n. is characterized in the genus by the following features in the female: body length (703–1070 µm) in the medium range for the genus, long cylindrical stoma (1.8–2.7 lip region diameters or 3.1–4.9 stoma diameters), metastom with two tooth-like denticles, cylindrical corpus without swelling, conspicuously cuticularized excretory duct, extremely long and expanded rectum (2.6–4.7 abd), spermatheca enlarging to dorsal side of oviduct, and conical tail with pointed tip (4.2– 7.9 abd or 1.5–2.1 rectal lengths). This species is probably hermaphroditic.

The present new species is apparently related to two genera, Dolichorhabditis Andrássy, 1983 and Oscheius Andrássy, 1976, recently emended by Andrássy (2005), on the basis of female/hermaphrodite having the extremely elongated rectum and conspicuous excretory duct. However, although male is unknown, the present species can be included into Dolichorhabditis in having the well developed long stoma (vs. short stoma in Oscheius) and metastom with setose denticles (vs. warts) as diagnostic characters of the genus (Andrássy, 2005). Dolichorhabditis consists of the following ten species (Andrássy, 2005), D. bengalensis (Timm, 1956) Andrássy, 2005, D. carpathica (Soós, 1941) Andrássy, 1983, D. debilicauda (Fuchs, 1937) Andrássy, 1983, D. dolichura (Schneider, 1866) Andrássy, 1983 (type species), D. dolichuroides (Anderson & Sudhaus, 1985) Andrássy, 2005, D. guentheri (Sudhaus & Hooper, 1994) Andrássy, 2005, D. pseudodolichura (Körner in Osche, 1952) Andrássy, 2005, D. rara (Körner, 1954) Andrássy, 1983, D. sechellensis (Potts, 1910) Andrássy, 2005, and D. tipulae (Lam & Webster, 1971) Andrássy, 2005.

Of the ten known species, D. tereticorpus sp. n. clearly differs from D. carpathica, D. debilicauda, and D. rara by the rectum length (2.6–4.7 abd length vs. less than 2 in the latter 3 species). The other seven species were previously treated as members of “ Dolichura -group” in Rhabditis (Oscheius) Andrássy, 1976 by Sudhaus & Hooper (1994) and Sudhaus & Fitch (2001). According to the key to species of the group in Sudhaus & Hooper (1994), D. tereticorpus is distinguished from D. guentheri, which has a rudimentary posterior gonad (vs. well developed and functional paired gonads in D. tereticorpus); D. bengalensis, which has a swollen or clavate tail terminus (Sudhaus, 1974) (vs. tail with pointed tip); and D. dolichura, with tail length less than 4 abd or 1.5 rectum lengths (e.g., Völk, 1950) (vs. 5.3±1.1 abd or 1.7±0.2 rectum lengths in D. tereticorpus). Of the remaining four species, D. tereticorpus resembles the gonochoristic D. dolichuroides in having a cylindrical corpus without swelling. However, the new species differs from D. dolichuroides by the short body length (L=703–1070 µm vs. 1167–1580 µm in D. dolichuroides), almost cylindrical midbody (vs. constricted at vulval region), pharyngeal lumen with no peculiar structure (vs. with a fine zipper-like structure), and vulva with smooth lips (vs. with thin, lamelliform lips). Of the three species characterized by having a pharynx with slightly swollen corpus, D. tereticorpus is somewhat similar to D. tipulae in general morphometric features but differs from it in having the dorsal flexures of ovaries not extending beyond oviduct and the spermatheca enlarging to the dorsal side of oviduct (vs. dorsal flexures extending to uterus or beyond vulva and spermatheca following oviduct longitudinally in D. tipulae; cf. Sudhaus, 1993). Dolichorhabditis tereticorpus is also distinguished from D. pseudodolichura and D. sechellensis by the combination of the following characters: medium body length (703–1070 µm), value of De Man’s ratios (b=4.5–6.0, c=7.6–12.7), four lateral lines, metastom with two denticles, shorter excretory duct and tail length (t=69–92): larger b value (6.6–8.0), metastom with five denticles and long excretory duct in D. pseudodolichura (Körner, 1954); smaller c value (5–6) and two lateral lines in D. sechellensis.

As mentioned above, the present new species has been erected in Dolichorhabditis here on the basis of the female characteristics, well developed long stoma, metastom with tooth-like denticles (setose teeth) and long rectum as diagnostic characters of the genus (Andrássy, 2005). This inclusion, however, may be reexamined if more data are obtained, particularly from male specimens, in future. Two known species, D. carpathica and D. rara, were also placed into this genus on the basis of female in Andrássy (1983, 1984, 2005), although they have rather shorter rectum (less than 1 abd length, calculated from the original drawings in Soós, 1941 and Körner, 1954, respectively). It seems appropriate to exclude these two species from Dolichorhabditis as treated in “ Dolichura -group” of Rhabditis (Oscheius) in Sudhaus & Hooper (1994).