Description of type material.
Two complete specimens,
typeStatusholotype
quantity9.7 mm
with 43 segments,
specimenCountone paratype
quantity8.4 mm
with 41 segments. Diameter at XI
quantity0.3–0.5 mm
. Prostomium usually conical. Clitellum well developed over XI–XII. Chaetae bifid, with upper teeth more or less as long as, and thinner than, or sometimes as thick as, lower (figure 2A). Chaetae
quantity
45–60
m
m long, about
quantity
2.5
m
m thick; (zero) one to two (three) per bundle anteriorly, zero to two 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 2B). Spermathecal pores paired in line with ventral chaetae in anterior part of X.
Pharyngeal glands well developed in IV–V. Chloragogen cells from VI onwards. Oesophagus in IX barrel-shaped, thick-walled and granulated, without chloragogen cells; semi-embedded blood plexus permeating entire region, with regular transverse vessels and less regular longitudinal ones.
Male genitalia (figure 2C, D) paired. Vas deferens (figure 2C, D: vd) short and wide, about
quantity
70
m
m long,
quantity
19–22
m
m wide, entering atrium apically. Ental part of atrial ampulla bilobed, thin-walled and dilated; lobes separated by constriction. First ‘lobe’ of ampulla (figure 2C, D: at1) conical or oval,
quantity
35–65
m
m long, maximally
quantity
39–53
m
m wide. Second ‘lobe’ oval (at2),
quantity
35–50
m
m long, maximally
quantity
39–44
m
m wide. Ectal part of atrial ampulla more duct-like, thick-walled, with numerous slender nuclei close to (figure 2C, D: ncc) and opposite to (nco) prostatic pad. This part
quantity
150–155
m
m long,
quantity
16–48
m
m wide. Prostatic pad (figure 2C, D: ppd) round,
quantity
46-48
m
m long, ventrally attached to middle of duct-like part of atrial ampulla (aa), bulging out from atrium. Prostate gland (figure 2C, D: pr) large, with small nuclei and large nucleus-like bodies, latter oblong or round, maximally
quantity
16
m
m long,
quantity
15
m
m wide. Atrial duct (figure 2C, D: ad) with (1) posterior blind sac (bs),
quantity
25–50
m
m long,
quantity
15–48
m
m wide, and (2) efferent duct (ed),
quantity
45–55
m
m long,
quantity
31–48
m
m wide, opening directly to exterior through simple pore. Sperm sac in IX–XII, or XI–XII. Egg sac in XII–XIII or absent. Spermathecae (figure 2B) large; ducts
quantity
75–105
m
m long,
quantity
36–48
m
m wide, with ectal vestibules; ampullae oblong, thin-walled,
quantity
145–195
m
m long,
quantity
50–75
m
m wide, with sperm masses in lumina.
Brief description of specimen from
collectingRegionHainan
.
Specimen complete,
quantity5 mm
long, 39 segments. Chaetae
quantity
45–55
m
m long, about
quantity
2.5
m
m thick, bifid, with equal teeth; one to two (three) per bundle anteriorly, one to two per bundle in post-clitellar segments. Male pores posterior to middle of XI. Male ducts somewhat twisted and difficult to make out. Spermathecae with oblong ampullae, but without sperm; specimen appears pre-copulatory.
Remarks.
This species is easily distinguished from all its congeners by its bilobed atrial ampullae, and low number of chaetae; latter usually no more than two per bundle or even absent. The atria have dorsal thickenings and clusters of slender nuclei around the prostatic pads, as well as blind sacs, suggesting a close relationship to
D. tener
.
In the new species, however, the vasa deferentia are shorter than those of the latter, and the prostatic pads are situated at mid-point of the atrium, as opposed to the more ental location in
D. tener
.
Although not all its features were clearly seen, the specimen from
collectingRegionHainan
has
fewer chaetae than
D. tener
, and appears to have blind sacs and clusters of slender nuclei in the atria. Therefore, it is identified as
D. bisaccus
, at least for the time being.
