Aulodrilus limnobius Bretscher, 1899

Ohtaka, Akifumi, 2021, Taxonomical study of Japanese Aulodrilus Bretscher (Annelida, Clitellata Tubificinae) with descriptions of two new species, Zootaxa 4952 (1), pp. 1-32 : 2-5

Aulodrilus limnobius Bretscher, 1899

( Figures 1 , 2 )

Aulodrilus limnobius Bretscher, 1899: 388 .

Aulodrilus limnobius Bretscher : Michaelsen 1900: 55; Piguet & Bretscher 1913: 58; Brinkhurst 1963: 66; 1965: 150, figs 9–10; 1971: 524, fig 8.23 G, H; 1986: 191; Brinkhurst & Cook 1966: 19, fig 7 T, U; Brinkhurst 1971: 524, figs 8.23 G, H; Hrabě 1981: 72; Davis 1982: 24, fig 8; Giani et al. 1984: 20, fig 2 C; Finogenova & Arkhipova 1994: 8, figs 1, 3, 4, 5, 19; Pinder & Brinkhurst 2000: 45.

Paranais tenuis Cernosvitov, 1937: 143 , figs 21–24.

Material examined. Japan: 30 immature specimens, Chubetsu-numa at 1790 m alt. of Mt. Chubetsu-dake, Taisetu Mountains , Hokkaido, 26 July 1983 . 8 immature specimens, Lake Takkobu, Kushiro City , Hokkaido, 23 July 2003 , coll. T. Ito . 12 immature specimens, Lake Bankei-numa at 910 m alt. of Mt. Soranuma-dake, Sapporo City , Hokkaido, 8 Aug. 1982, 2 July 1983 . 3 immature specimens, offshore Lake Okotanpe, Chitose City , Hokkaido (15–20 m in depth), 4 Aug. 1984 . 13 mature and 10 immature specimens, rice paddy in Nozawa, Aomori City , Aomori Prefecture, 28 June, 2007 . 4 immature specimens, rice paddy in Kanagi, Goshogawara City , Aomori Prefecture, 1 July 2000 . 3 immature specimens, Lake Hiyamizu-numa, Tsugaru City , 1 July 2007 . 10 immature specimens, rice paddy in Inakadate Village , Aomori Prefecture, 3 June 2011 . 8 immature specimens, rice paddy in Utarube, Towada City , Aomori Prefecture, 5 June 2011 . 3 mature and 4 immature specimens, rice paddy in Shin-hoshi, Hirosaki City , Aomori Prefecture, 29 June, 2014. 10 mature and 25 immature specimens, rice paddy in Zatoishi, Hirosaki City , Aomori Prefecture, 18 June 2011 . 5 immature specimens, rice paddy in Orikasa, Hirosaki City , Aomori Prefecture, 25 June 2011 . 5 mature and 15 immature specimens, rice paddy in Ichoda, Hirosaki City , Aomori Prefecture, 25 June 2011 . 13 immature specimens, a marsh in Sakamoto, Hirosaki City , Aomori Prefecture, 25 Sep. 2011 . 5 mature and 7 immature specimens, rice paddy in Ohkawara, Kuroishi City , Aomori Prefecture, 16 Aug. 2011 . 3 immature specimens, Aseishigawa Reservoir, Kuroishi City , Aomri Prefecture, 4 Aug. 2014 . 5 mature and 7 immature specimens, rice paddy in Shichinohe Town , Aomori Prefecture, 24 June 2007, 16 Aug. 2011 . 20 immature specimens, rice paddy in Ishizawa, Gonohe Town , Aomori Prefecture, 16 Aug. 2011 . 5 immature specimens, rice paddy in Muranaka, San-nohe Town , Aomori Prefecture, 16 Aug. 2011 . 10 mature and 20 immature specimens, rice paddy in Iwaihana, Hachimantai City , Iwate Prefecture, 15 July 2007 . 2 immature specimens, Lake Hachiro-gata , Akita Prefecture (3.6m depth), 9 July, 2005 . 1 immature specimen, a marsh in Osawa near Lake Tazawa, Senboku City , Akita Prefecture, 29 Sep. 2007 . 3 mature and 20 immature specimens, rice paddy in Gojome Town , Akita Prefecture, 17 July 2011 . 10 mature and 9 immature specimens, rice paddy in Hinai, Odate City , Akita Prefecture, 22 July 2011 . 5 immature specimens, rice paddy in Akafuchi, Kazuno City , Akita Prefecture, 16 July, 2007. 100 mature , 20 immature specimens, rice paddy in Tajiri, Osaki City , Miyagi Prefecture, 25 Jul. 2007, coll. M. Kawase. 5 mature and 18 immature specimens, rice paddy in Tome City , Miyagi Prefecture, 27 May 2007 . 3 mature specimens, rice paddy in Fujishima, Tsuruoka City , Yamagata Prefecture, 30 June 2006, coll. M. Kawase. 1 immature specimen, rice paddy in Obanazawa City , Yamagata Prefecture, 9 Aug. 1990 . 5 immature specimens, rice paddy in Tomioka City , Gunma Prefecture, 16 Aug. 1985 . 2 mature and 28 immature specimens, rice paddy in Oki, Takasaki City , Gunma Prefecture, 24 July 1995 . 4 mature specimens, a small current in Ozegahara mire, Gunma Prefecture, 26 Jul. 1995, 8 May 1998 . 3 mature and 10 immature specimens, rice paddy in Hotaka, Azumino City , Nagano Prefecture, 3 Aug. 2007 . 1 immature specimen, off Hayasaki, Lake Biwa , Shiga Prefecture (33 m in depth), 29 Sep. 1992 . 3 immature specimens, off Wani, L. Biwa , Shiga Prefecture, 13 Apr. 1993 . 2 immature specimens, Zeze Park, Otsu City, Shiga Prefecture, 9 July , 1999. 10 mature and 14 immature specimens, rice paddy in Hiruta, Yasu City , Shiga Prefecture, 1 June 2009, coll. M.J. Grygier. 4 immature specimens, Ukasho, Yasuki City , Shimane Prefecture, 2 Mar. 2015, coll. N. Kado. 1 immature specimen, rice paddy in Nangoku City , Kochi Prefecture, 24 Mar 2007 . 1 immature specimen, Isahaya Bay , Saga Prefecture, 11 Dec. 2000, coll. M. Azuma. Altogether 191 mature and 357 immature specimens from Japan. China : 1 immature specimen, offshore Lake Erhai , Yunnan Province, 13 May 1992, coll. M. Nishino. U.S.A.: 2 immature specimens, Oregon, U. S.A. (detailed collection data unknown), coll. R. O. Brinkhurst . 12 immature specimens, Yakima River , Washington (detailed locality unknown), 29 Oct. 1987 , coll. S. V. Fend. 8 mature specimens, Tuolumne River, San Joaquin , California, coll. S. V. Fend . Russia: 2 immature specimens, a nameless stream near Khabarovsk in the tributary of Amur River, 20 Sep. 1992 .

Description. In fixed state, body length 10–13 mm, width 0.28 mm at middle of body, with up to 130 segments. Posterior 1/7–1/8 of body without chaetae and unsegmented, with many transverse furrows. Prostomium bluntly conical: length less than half of the width in segment I. Body wall 15–25 µm thick, uneven, with several transverse furrows in each segment. Pharynx in II and III, dorsal wall up to 50 µm thick, much thicker than ventral wall. Pharyngeal glands weakly developed. Intestine with thin wall, and with spacious cavity in middle and posterior segments. Chloragogen cells less than 15 µm in height from VI on, a thin layer on gut. Transverse vessels forming complicated loops in II–VII, thick in VIII and IX as hearts ( Fig. 1E ).

Chaetae all bifid crotchets; the form, size and number not different between dorsal and ventral bundles. In several anterior segments, chaetae ( Fig. 1 A ) up to 9 per bundle, 41–50 µm long, slightly shorter, thicker and more strongly curved than those in the remaining segments; nodulus situated distal to midpoint, and distal teeth parallel: upper tooth about half as long as, and much thinner than lower one. From VII or VIII on, chaetae up to 7 per bundle, 43–58 µm long, with nodulus at 1/3 or less from distal end, distal ends with lateral wings ( Fig. 1 B, C ); distal teeth parallel, with upper tooth more than half as long as and much thinner than the lower one. Lateral wings on chaetae made up by lateral expansions along the axis on the convex side of chaeta ( Fig. 1D ), extending from slightly distal to nodulus to base of the upper tooth. Maximum width of lateral wings 2.4–2.9 µm. Dorsal and ventral chaetae in II and III often fewer (2 or 3 per bundle) than those in later segments. Ventral chaetae in genital segments not modified.

Clitellum surround the segments from 1/2 VI to end of VIII; the genital segments longer than the rest. Testes two pairs, in V and VI; latter pair larger than the former, and ovaries one pair in VII ( Fig. 1F ). Male funnels small, 50 µm in diameter. Vasa deferentia about 200 µm long and 30 µm wide, winding in the middle course, connected with atria apically. Atria stoutly tubular, 130 µm long by 60 µm wide; the inner epithelium tall and glandular. Prostate glands large, connected with atria laterally through a short stalk. Ejaculatory ducts not detected. Penes large in deep and folded chambers ( Fig. 1F ), which open separately, just lateral to ventral chaetal bundles in VII. Spermathecae in VI, opening laterally and anterior to the dorsal chaetal bundles ( Fig. 1F ); ampullae ovoid and ducts short. Loose sperm found in the ampullae. Sperm sac in V–VII. Egg sac in VI–VII.

Making a tight tube from detritus together with mucus secreted from the body wall. Body not coiled up when a live worm is removed from mud tube and stimulated. Cocoon spindle to ovoid in shape, 520–600 µm long by 300–400 µm wide, covered with fine mineral particles ( Fig. 2A ). Operculae of cocoon 40–60 µm in diameter, dis- tinct on one end of the long axis, but somewhat inconspicuous in the opposite one. The cocoons invariably contain a single embryo which occupies the whole volume of the cocoon ( Fig. 2B ).

Remarks. This species was distinguished by the absence of hair chaetae and presence of prominent lateral wings on the bifid chaetae. The form of male reproductive organs in the present specimens agrees with the descriptions by Hrabě (1981), Giani et al. (1984) and Finogenova & Arkhipova (1994).

Distribution. This is a cosmopolitan species ( Brinkhurst 1971). In Japan it is common in lakes and ponds, especially shallow waters. These are often the most abundant oligochaetes in paddy fields in Japan ( Ohtaka 2018b).

Figures

FIGURE 1. Aulodrilus limnobius Bretscher from Japan. A, ventral chaeta in V; B, dorsal chaeta in a mid-segment, dorso-lateral view; C, the same, lateral view; D, SEM photomicrograph of dorsal chaetae in a mid-segment; E, lateral view of anterior segments, showing vascular system; F, parasagittal section of genital segments. A–D from Lake Okotanpe, Chitose, Hokkaido Prefecture, Japan; E from Tajiri, Osaki, Miyagi Prefecture, Japan; F from Ozegahara mire, Gunma Prefecture, Japan.

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.