Aulodrilus apeniatus, Cui, Yongde & Wang, Hongzhu, 2009

Cui, Yongde & Wang, Hongzhu, 2009, Three new species of Tubificinae, Oligochaeta, from two plateau lakes in Southwest China, Zootaxa 2143, pp. 45-54 : 50-51

Aulodrilus apeniatus n. sp.

Holotype: IHB YAN 20020813d, whole-mounted specimen.

Type locality: About 1 km in front of Gehe River mouth (24º22΄58΄ N, 102º49΄49΄ E) in Fuxian Lake, eastern Yunnan, China; depth 41 m, bottom temperature 17.6°C, dissolved oxygen at bottom 8.2 mg /L, total nitrogen in water 0.299 mg /L, total phosphorus in water 0.023 mg /L, fine clay; 8 Aug 2002, coll. Y. Cui & X. Liu.

Etymology: The specific name “ apeniatus ” is Latin for “without penis”, and refers to the absence of penis in this species.

Description: Specimen incomplete, length> 12.8 mm, diameter at XI about 0.4 mm, segments> 80. Clitellum inconspicuous.

Dorsal chaetae 1–4 hairs and 2–4 bifids per bundle; hairs slender and long, without serration, 260–320 µm long anteriorly, and 180–220 µm long in postclitellar segments; bifids ( Fig. 3 C) pectinate, 80–120 µm long, 2.0–3.0 µm thick, upper prong, slightly longer or as long as, and thinner than lower, with 2–3 thin intermediate teeth. Ventral chaetae ( Fig. 3 A–B) bifid, 1–4 per bundle, 75–88 µm long, 3.0–3.2 µm thick, with upper prong conspicuously longer and slightly thinner than lower. Ventral chaetae unmodified in X and absent in XI. Male pores paired in line with ventral chaetae, posterior to middle of XI. Spermathecal pores paired in line with ventral chaetae in mid-X.

Pharyngeal glands in II–III. Chloragogen cells from VI onwards. No coelomocytes. Male genitalia ( Fig. 3 D) paired. Vas deferens ( Fig. 3 D, vd) 86–110 µm long, 15–25 µm wide, entering atrium subapically. Atrium ( Fig. 3 D) club-shaped, transition between ampulla and duct gradual. Atrial ampulla ( Fig. 3 D, aa) ovoid, 110–120 µm long, 35–68 µm wide, atrial duct ( Fig. 3 D, ad) 90–160 µm long, 20–35 µm wide. Solid prostate gland ( Fig. 3 D, pr) large, attached to ental atrium by short stalk. Penis absent.

Spermathecae ( Fig. 3 D, sa) paired, small, elongated, 50–75 µm long, 35–45 µm wide, with indistinct duct, and without sperm in ampulla.

Distribution and habitat: Known only from type locality, Yunnan Province, China. Freshwater lake, 40 m depth, water temperature about 17 ºC, fine clay.

Remarks: The short vasa deferentia, the ovoid atria with solid prostate glands, the spermathecae without distinct ducts and the absence of penial chaeta and coelomocytes indicate that the new species fits more closely the definition of Aulodrilus Bretscher, 1899 ( Brinkhurst & Jamison, 1971) than that of other described genera.

Aulodrilus apeniatus n. sp. having no penis is a unique feature of Aulodrilus . With regard to the simple atria and the dorsal bifids, A. apeniatus is similar to A. pectinatus , but it differs from the latter by the slender hairs, the pectinate chaetae throughout the body and the absence of penial chaeta.

As a rule, most Aulodrilus species have distinctive somatic chaetae, as bifid chaetae with short upper teeth, and posterior end modified into a respiratory organ ( Finogenova & Arkhipova, 1994). These features are absent in the present species. The new species is assigned to Aulodrilus according to the male genitalia, but the external morphological characteristics. The described specimen of A. apeniatus is seemingly a single, unmated animal, and the structure of sexual organs that could be still in a phase of development. So, we gave a provisional home for it, and its systematic placement needs further confirmation from more specimens.

Figures

FIGURE 3. Aulodrilus apeniatus. A – B. ventral chaetae; C. dorsal bifid; D. lateral view of spermathecae and male ducts in segments X – XI. Scale bars: A – C 40 µm; D 200 µm.