Aulodrilus pluriseta ( Piguet, 1906 )

Ohtaka, Akifumi, 2021, Taxonomical study of Japanese Aulodrilus Bretscher (Annelida, Clitellata Tubificinae) with descriptions of two new species, Zootaxa 4952 (1), pp. 1-32 : 7-9

Aulodrilus pluriseta ( Piguet, 1906)

( Figure 5 )

Naidium pluriseta Piguet, 1906: 218 .

Aulodrilus pluriseta (Piguet) : Brinkhurst 1971: 525, fig 8.23K (in part); Hrabě 1981: 67, pl XI, figs 11–15. Giani et al. 1984: 20, fig 2A, B; Finogenova & Arkhipova 1994: 11, figs 11–13, 20–22; Timm 1999b: 90; Arslan & Sahin 2003: 276, fig. 2.

Aulodrilus trivandranus Aiyer, 1925: 36 , figs 6–9.

Material examined. Japan: 1 immature specimen, Lake Hiyamizu-numa, Tsugaru City, Aomori Prefecture, 16 July. 2005 . 5 immature specimens, Takahamairi Bay, Lake Kasumigaura , Ibaraki Prefecture, 9 Feb. 2011 . 2 immature specimens, offshore Lake Inba-numa , Chiba Prefecture, 9 Mar. 2009 . 2 immature specimens, Lake Nishi-no-ko near Lake Biwa, Ohmi-Hachiman City , Shiga Prefecture, 8 Aug. 2001 . 1 immature specimen, Pond Otome-ga-ike near Lake Biwa, Takashima City , Shiga Prefecture, 19 Mar. 2002 . 3 immature specimens, Pond Sone-numa near Lake Biwa , Hikone City, Shige Prefecture, 12 Dec. 2001, 11 Mar. 2002 . 1 immature specimens, littoral Lake Biwa , Shiga Prefecture, 14 Feb. 1994 . 1 immature specimen, rice paddy, Izumo City , Shimane Prefecture, 24 July 2015 . U.S.A.: USNM 58782 , an immature specimen, Cayuga Lake, New York, 20 May , 1974, coll. D. R. Spencer . Russia: 5 mature and 15 immature specimens, Rybinsk Reservoir on the Middle Volga River, coll. N. R. Arkhipova; cultured at the Võrtsjärv Limnological Station, Estonia by T. Timm since 1987 and sampled in 11 Oct. 2006 .

Description. All of the Japanese specimens were immature; identified mainly based on the chaetal morphology. Chaetal characteristics in Japanese specimens as follows: Dorsal chaetal bundles consisting of hair and bifid crotchets, both beginning in II. Hair chaetae ( Fig. 5A ) smooth and slightly sigmoid in shape, 3–8 per bundle, 160–256 µm long in anterior segments, 0–4 per bundle, 144–173 µm long in posterior segments. Dorsal crotchets ( Fig. 5B,C ) with nodulus situated at 1/3–1/4 from distal ends, 6–8 per bundle, 64–104 µm long in anterior segments, 3–5 per bundle, 56–80 µm long in posterior segments; distal teeth weakly divergent with upper tooth 1/2–2/3 as long as and thinner than lower tooth ( Fig. 5E,F ). Ventral chaetae ( Fig. 5D ) bifid crotchets with nodulus situated at 1/3–1/4 from distal ends, 10–15 per bundle, 64–80 µm long in anterior segments, 5–8 per bundle, 56–67 µm long in posterior segments; distal teeth parallel, and upper tooth shorter and thinner than lower. Shafts of both dorsal and ventral crotchets slightly widened laterally beneath distal teeth ( Fig. 5G ).

Mature specimens from Russia have the atrial segment (VII) swollen laterally, with male pores opening at the ventral side of the right and left expansion ( Fig. 5H ). Vasa deferentia 340 µm long, longer than atria. Atria crescentshaped, 260 µm long, 60–80 µm wide, receiving a petiolate prostate gland at concave side ( Fig. 5I ). Ejaculatory ducts short and muscular, leading to conical penes. Spermathecae with short ducts and large saccular ampullae, opening on lateral sides in VI ( Fig. 5I ). Alimentary canals with thin chloragogen cells from VII on, widening abruptly in VIII or IX ( Fig. 5H ).

Remarks. Aulodrilus pluriseta is distinguishable from congeners by having dorsal hairs from II and bifid chaetae with upper teeth shorter and thinner than lower teeth. Crescent-shaped or oval atria, short ejaculatory ducts and conical penes found in the present Russian specimens agree with earlier descriptions by Hrabě (1981), Giani et al. (1984), and Finogenova & Arkhipova (1994). Spermathecae consisting of a large saccular ampullae and short ducts opening laterally in the present Russian material also coincide with an earlier description by Finogenova & Arkhipova (1994). By contrast, Giani et al. (1984: Fig. 2b ) described tubular spermathecal ampullae in their A. pluriseta . Aiyer (1925) described narrow and elongate spermathecal ampullae in A. trivandranus , a species that has been synonymized with A. pluriseta by Brinkhurst (1971). The differences in the shape of spermathecal ampullae might indicate that nominal A. pluriseta consists of more than one species, but it is also probable that spermathecal ampullae change in form and size depending on the degree of maturation or the volume of sperm received.

Aulodrilus sp. reported by Brinkhurst et al. (1990) from Guandong and Shandong Provinces in China resembles A. pluriseta in having hair and bifid chaetae in dorsal bundles. However, the distal teeth of anterior dorsal chaetae in the Aulodrilus sp. have equal length and thickness. The species is different from A. pluriseta , in which the upper teeth of dorsal chaetae are invariably shorter and thinner than the lower teeth. In addition, the Aulodrilus sp. has unique long, coiled, and heavily muscular spermathecal ducts, which are not found in any other congener. It is probable that this material represents a distinct undescribed species.

Figures

FIGURE 2. Cocoons of Aulodrilus limnobius Bretscher from Tajiri, Osaki, Miyagi Prefecture, Japan. A, outer appearance, drawing; B, cross section, photograph. Cocoons were collected in 2007 from a population reared in the laboratory.

FIGURE 5. Aulodrilus pluriseta (Piguet) from Lake Kasumigaura, Japan (A–G) and from Estonia (H and I). A, dorsal hair chaeta in an anterior segment; B, dorsal crotchet in IV; C, dorsal crotchet in a posterior segment; D, ventral chaeta in VIII; E and F, distal ends of dorsal crotchets; G, ventral view of distal end of ventral chaeta in anterior segment; H, ventral view of anterior segments showing locations of alimentary canal and genital organs; I, ventral view of genital segments. H and I are from one whole-mounted specimen.