Doliodrilus diverticulatus Erséus, 1985

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 : 283-285

Doliodrilus diverticulatus Erséus, 1985

(figure 7)

Doliodrilus diverticulatus Erséus, 1985: 144–146 , figure 11; Erséus, 1997b: 120–121; Erséus, 1997c: 443–444; Gustavsson and Erséus, 1999: 473–476, figure 5f, table 1 .

New material. IHB HANA2000003 a, one specimen from SY00-2A . SMNH Main Coll. 43681, one specimen from HU00-19A .

Brief description of new material. One complete specimen 3.5 mm long, about 30 segments. Diameter at XI 0.3–0.4 mm. Prostomium conical. Clitellum extending over XI–XII. Chaetae 50–55 m m long, about 2.5 m m thick, with upper teeth variable in length, ranging from longer to shorter than lower teeth (figure 7A); (two) three to four (five) per bundle anteriorly, one to three per bundle in post-clitellar segments. Chloragogen cells from VI onwards. Unpaired ventral diverticulum in IX variable; in specimen from SY00-2A, diverticulum (figure 7F: od) only about 85 m m long, 40–50 m m wide, covered with cell projections, and without reticulate blood plexus; in specimen from HU00-19A, diverticulum (figure 7E: od) larger, about 200 m m long, 80–90 m m wide, with conspicuous, more or less regular, blood plexus; moreover, in latter specimen, although less distinct, plexus developed also on other parts of the gut in IX–XII. Vasa deferentia (figure 7D: vd) about 100 m m long, 10 m m wide. Atria slender, totally 135–160 m m long, 7–22 m m wide; ental part not thin-walled, tapering off on to vasa. Prostatic pads (figure 7D: ppd) somewhat triangular, about 24 m m long. Prostate gland (pr) medium-sized, with oblong or round nuclei, latter maximally 7 m m long and 6 m m wide. Atrial ducts (figure 7D: ad) each with (1) posterior blind sac (bs), 20–25 m m long, 10–35 m m wide, and (2) efferent duct (ed), 15–25 m m long, 17–24 m m wide. Spermathecal ducts 30–35 m m long, 12–29 m m wide; ampullae 50–55 m m long, 10–35 m m wide (figure 7B, C); only the specimen from HU00-19A post-copulatory, with a few scattered spermatozoa in lumina of ampullae (figure 7B).

Remarks. This species was originally described from Saudi Arabia, and subsequently reported also from Darwin Harbour (Erséus, 1997b) and Montebello Islands (Erséus, 1997c) in Australia. The new material conforms to the previous descriptions (Erséus, 1985, 1997b, 1997c) in most aspects, particularly, with regard to male ducts.

The unpaired diverticulum was first described as ‘dorsal’ (Erséus, 1985), but was later shown to be attached to the ventral side of the oesophagus and from there to run upwards along one lateral side of the segment (Erséus, 1997c; Gustavsson and Erséus, 1999). The new material conforms with the latter description. However, the diverticulum is variable in size, a large one being over twice as long as a small one. Such a variation was confirmed also by re-examination of the specimens from Saudi Arabia (treated by Erséus, 1985) and Darwin Harbour (treated by Erséus, 1997b), which all have similar body size. In the Saudi Arabia material, the diverticulum is 100–180 m m long, 40–70 m m wide, and in that from Darwin Harbour, it is about 250 m m long, 100 m m wide.

Referring to the blood plexus, it is absent or present in the diverticulum of the new material, and when present it may even extend more broadly on to the gut. Gustavsson and Erséus (1999) noted the irregular blood plexus in the diverticulum of Darwin Harbour worms, but on re-examination of that material, we found it also to be present in other parts of the gut in segments IX–1/3X. In the Saudi Arabian form, we also observed the irregular blood plexus in the diverticulum. Hence, a blood plexus is generally present in the diverticulum in D. diverticulatus , but it is less regular than in other species.

In the original description by Erséus (1985), the clitellum is stated to extend over XI–1/2XII, but a re-examination of his material showed that it actually reaches the end of XII in some specimens. The new material falls within this variation.

Distribution and habitat. Southern China (new record), Western Australia and Northern Territory in Australia, and Saudi Arabia. Brackish-water to marine, intertidal and subtidal in mangroves, sand and mud.