Doliodrilus sp.

Wang, Hongzhu & Erséus, Christer, 2004, New species of Doliodrilus and other Limnodriloidinae (Oligochaeta, Tubificidae) from Hainan and other parts of the north-west Pacific Ocean, Journal of Natural History 38 (3), pp. 269-299 : 280-281

Doliodrilus sp.

(figure 5)

Material examined. IHB HANA2000029 a–b, two whole-mounted specimens from Station HU-19A. SMNH Main Coll. 43680, one specimen from HU-19A .

Description. Two complete specimens, 5.6–6.8 mm long, 45–46 segments. Diameter at XI 0.2–0.3 mm. Prostomium blunt. Clitellum well developed over XI–1/2XII (XII). Chaetae bifid, with upper teeth thinner than, and as long as, lower (figure 5A). Chaetae 50–65 m m long, about 2.5 m m thick; two to four per bundle anteriorly, (one) two to three per bundle in post-clitellar segments. Ventral chaetae absent in XI. Male pores paired, in line with ventral chaetae in posterior part of XI (figure 5C). Spermathecal pores paired, in line with ventral chaetae in anterior part of X.

Pharyngeal glands in IV– V. Chloragogen cells from VI onwards. Oesophagus in IX barrel-shaped, thick-walled and granulated, with reticulate blood plexus but without chloragogen cells.

Male genitalia (figure 5C) paired. Vas deferens inconspicuous, estimated to be about as long as atrium, but unclear whether it enters latter apically or subapically. Atrium totally about 150 m m long, 15–30 m m wide, somewhat club-shaped; ental part of atrium dilated but not thin-walled; wall opposite prostatic pad somewhat thicker than other part of ampullar wall, but thickening without clusters of slender nuclei (figure 5C: aa). Prostatic pad (ppd) large and round, 36 m m long, situated ventrally one-third down atrium from apical end. Prostate gland (pr) large, with small nuclei and large nucleus-like bodies, latter oblong to round, maximally 12 m m long, 10 m m wide. Atrial duct (figure 5C: ad) with (1) small posterior blind sac (bs), about 20 m m long, 12–17 m m wide, and (2) short efferent duct (ed), about 20 m m long, 14 m m wide. Sperm sac in XI. Egg sac in XII. Spermathecae (figure 5B) small; ducts short, about 27 m m long, up to 24 m m wide, with ectal vestibules; ampullae oblong, 90 m m long, 30–50 m m wide, with sperm masses in lumina.

Remarks. With regard to the male ducts, this form appears closely related to D. tener . However, there are substantial differences. First, the ental parts of its atria are not thin-walled and dilated as in the latter. Second, its prostatic pads are more entally located and somewhat bigger than those of D. tener . Third, there are no clusters of slender nuclei around its prostatic pads. Hence, this form is likely to be a separate species. However, considering that two of the specimens are partly damaged, and the male ducts of the other are obscured by food particles, we do not name it for the time being.

In one of the studied specimens, the posterior end bears commensal ciliates, similar to those reported by Erséus (1990a: 295, figure 15H).

Distribution and habitat. Known only from one locality in Hainan, China. Brackish-water, subtidal, sandy mud.