Doliodrilus bidolium, Wang & Erséus, 2004

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 : 289

Doliodrilus bidolium sp. n.

(figure 10)

Holotype. IHB HANA2000009 af, whole-mounted specimen.

Type locality. China, southern Hainan, brackish-water pond near Teng Hai (E of Sanya City) (Station SY00-6).

Paratypes. IHB HANA2000009 ag–aj, four specimens from type locality . SMNH Type Coll. 5480–5484, five specimens from type locality .

Etymology. The specific name bidolium, Latin meaning ‘two small barrels’, alludes to the modified oesophagus, which in VIII–IX is thick-walled, granulated, and bearing a reticulate blood plexus.

Description. Two complete specimens, holotype 11.0 mm with 58 segments, one paratype 9.8 mm long, 50 segments. Diameter at XI about 0.5 mm. Prostomium blunt. Clitellum more or less developed over XI–XII. Chaetae (figure 10A) bifid, with upper teeth thinner and shorter than, or as long as, lower. Chaetae 45–55 m m long, about 2.5 m m thick; (one) two to four per bundle anteriorly, one to three per bundle in post-clitellar segments. Ventral chaetae absent in XI. Male pores paired, in line with ventral chaetae in mid-XI (figure 10D). 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 posterior two-thirds of VIII and whole of IX thick-walled and granulated, constricted at septum 8/9, without or with chloragogen cells; semi-embedded blood plexus permeating entire region, with regular transverse vessels and less regular longitudinal ones.

Male genitalia (figure 10D) paired. Vas deferens (figure 10D: vd) short, 50–60 m m long, 7–10 m m wide, entering atrium apically. Atrium (figure 10D: a) slender and somewhat spindle-shaped, about 185 m m long, 12–27 m m wide; ental part tapering off on to vas but not thin-walled; ectal part slightly dilated and opening to exterior through simple pore. Prostatic pad (figure 10D: ppd) round, about 30 m m long, ectally situated, i.e. about one-third up atrium from male pore; pad bulging out from atrium. Prostate gland (pr) medium-sized, with small nuclei and large nucleuslike bodies, latter oval to round, maximally 10 m m long, 7 m m wide. Sperm sac inconspicuous. Egg sac in XI–XII or XI. Spermathecae (figure 10B, C) small; ducts about 50 m m long, 17–27 m m wide, with ectal vestibules; ampullae oval and thickwalled, about 35 m m long, 30–40 m m wide, with few scattered sperm (figure 10B) or distinct sperm bundles (figure 10C) in lumina.

Remarks. In this new species, the modification of the oesophagus extends forward into, and through a large part of, VIII, which is a feature unique within the subfamily Limnodriloidinae . With regard to the simple atria and the position of the male pores, D. bidolium is similar to D. puertoricensis , but it differs from the latter by its shorter vasa deferentia and its more ectal position of the prostatic pads in the atria.

Distribution and habitat. Known only from type locality, southern China. Brackish-water, muddy sand.