Doliodrilus ciliatus, 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 : 278-279

Doliodrilus ciliatus sp. n.

(figure 4)

Holotype. IHB HANA2000023 b, whole-mounted specimen.

Type locality. China, northern Hainan, mangroves of Dong Zhai Harbour nature reserve (Station HU00-14B).

Etymology. The specific name ciliatus is Latin for ‘furnished with cilia’ and refers to the ciliated atria.

Description. Specimen complete, 12.0 mm, 69 segments. Diameter at XI 0.5 mm. Prostomium conical. Clitellum extending over XI–1/2XII. Chaetae bifid, with upper teeth about twice as long as lower (figure 4A). Chaetae 70–85 m m long, about 2.5 m m thick; two to five per bundle anteriorly, 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 4B). Spermathecal pores paired, in line with ventral chaetae in X, at about one-third of segment from anterior septum (figure 4B).

Pharyngeal glands well developed in IV– V. Chloragogen cells from VI onwards. Anterior third of oesophagus in IX unmodified, with wall only 25–35 m m thick. Posterior two-thirds of oesophagus in IX barrel-shaped, granulated, with wall up to 70 m m thick, but without chloragogen cells; semi-embedded blood plexus present, but inconspicuous, with regular transverse vessels and less regular longitudinal ones.

Male genitalia (figure 4B) paired. Vas deferens not clearly visible, estimated to be about as long as atrium, entering latter subapically (?). Atrium tubular, totally 230 m m long, 17–27 m m wide; ental part of atrial ampulla densely ciliated, thinwalled and somewhat dilated; ectal part of ampulla more thick-walled, and with wall containing more nuclei (figure 4B: aa). Prostatic pad (ppd) oval, 31 m m long, ventrally situated, bulging out from middle of atrium. Prostate gland (pr) large, with small nuclei and large nucleus-like bodies, latter oblong, round or irregularly polygonal, maximally 14 m m long, 10 m m wide. Atrial duct (figure 4B: ad) with (1) posterior blind sac (bs), about 30 m m long, 10–15 m m wide, and (2) short efferent duct (ed), about 30 m m long, 25 m m wide, opening directly to exterior through simple pore. Sperm sac extending through IX–X. Egg sac in XII–XIII. Spermathecae (figure 4B: s) club-shaped; ducts 110 m m long, 27–34 m m wide, with small, but distinct ectal vestibules; ampullae oval, thin-walled, 120 m m long, up to 77 m m wide, with sperm bundles in lumina.

Remarks. Initially, we hesitated to assign this species to the genus Doliodrilus , as the ental parts of its atria are ciliated, a character formerly considered to be an autapomorphy of Smithsonidrilus Brinkhurst, 1966 (Limnodriloidinae) (Erséus, 1990b). However, D. ciliatus has a dilated oesophagus in segment IX, and although indistinct, there is an oesophageal blood plexus in this segment. This type of modification as well as the atrial blind sacs are characteristic of most Doliodrilus , and thus, it is reasonable to conclude that this species belongs to the latter genus. With regard to the chaetal morphology and male ducts, D. ciliatus appears to be closely related to D. longidentatus sp. n. described above, but it is easily differentiated from the latter and other congeners by its ciliated atria, and the short length of the modified part of the oesophagus in segment IX.

Distribution and habitat. Known only from type locality, southern China. Lower intertidal in mangroves, clay and mud.