Aulodrilus dentosus, Ohtaka, 2021

Ohtaka, Akifumi, 2021, Taxonomical study of Japanese Aulodrilus Bretscher (Annelida, Clitellata Tubificinae) with descriptions of two new species, Zootaxa 4952 (1), pp. 1-32 : 13-16

Aulodrilus dentosus sp. nov.

( Figures 9 , 10 )

Holotype. NSMT-An 625, a mature specimen, 22 June 1982, coll. H. Kikuchi. Anterior part of the body sagittally sectioned and mounted on two slides and the posterior one whole-mounted on another slide.

Type locality. Offshore Lake Kitaura , Ibaraki Prefecture, Japan (36.016N, 140.566E), 6 m deep with muddy bottom .

Paratypes. NSMT-An 626, a cross-sectioned mature specimen from the type locality on one slide, 16 July 1982, coll. H. Kikuchi; NSMT-An 627, a whole-mounted mature specimen from the type locality, 22 June, 1982, coll. H. Kikuchi.

Other material examined. Japan: 3 immature specimens, offshore Lake Toro, Shibecha Town , Hokkaido, 6 June 2000 , coll. T. Ito. 5 mature and 20 immature specimens, offshore Lake Takkobu, Kushiro City , Hokkaido, 23 July 2003 , coll. T. Ito . 6 immature specimens, littoral Lake Barato, Sapporo City , Hokkaido, 12 Oct. 1983 . 5 immature specimens, littoral Lake Ogawara, Kamikita Town , Aomori Prefecture, 21 Sep. 2003 . 2 immature specimens, offshore Lake Hachiro-gata , Akita Prefecture (3.6 m depth), 9 July, 2005 . 1 immature specimen, offshore Lake Izunuma, Tome City , Miyagi Prefecture, 7 June 2008 . 42 mature and 87 immature specimens, offshore Lake Kitaura (type locality), 29 May , 14 June, 3 July 1980 ; 28 Oct., 20 Nov. , 26 Dec. 1981, 16 Mar. 1982 ; 19 Apr., 20 May, 22 June , 16 July , 26 Aug. , 29 Sep., 26 Nov. 1982 ; 14 Apr., 17 May, 25 June , 14 July , 3 Aug. , 15 Dec. 1983 ; 14 Feb., 18 May, 14 June , 16 July , 17 Aug. , 14 Sep. 1984; 5 Jan. 1985 . 3 immature specimens, Mizuhara, Lake Kitaura , Ibaraki Prefecture, July 1981 . 10 immature specimens, offshore Lake Kasumigaura , Ibaraki Prefecture, 10 Jan.1984; 9 Oct. 1985; 9 Feb. 2011 , coll. T. Iwakuma . 3 immature specimens, offshore Lake Inba-numa , Chiba Prefecture, 9 Mar. 2009 . 3 mature and 2 immature specimens, offshore Lake Kahoku-gata , Ishikawa Prefecture, 11 Aug. 1999, coll. M. Nishino. 2 mature and 4 immature specimens, offshore Lake Suwa , Nagano Prefecture, 18 Oct. 1980 . 2 immature specimens, offshore Lake Yogo, Nagahama City , Shiga Prefecture, 7 May 2000, coll. M. Nishino. 8 immature specimens, offshore Lake Koyama-ike , Torrori City Torrori Prefecture, 16 Mar. 2010 . 2 immature specimens, Kanna Reservoir, Ginoza Village, Okinawa Island , Okinawa Prefecture, 14 May 2018 , collector unknown. Altogether 55 mature and 158 immature specimens.

Etymology. The specific epithet refers to the form of the distal ends of the dorsal chaetae, having several teeth.

Description. In fixed state, length 10–20 mm, maximum width 0.36 mm in clitellum, 0.2–0.27 mm in mid-segments; 85–125 segments. Prostomium bluntly conical. Posterior segments (less than 1/10 of body length) without chaetae. No secondary annulation, but many narrow transverse furrows present. In anterior segments, epidermis 13–20 µm thick with many glandular cells staining deeply with hematoxylin. Pharynx in II and III; pharyngeal glands weakly developed dorsally ( Fig. 10A ). Chloragogen cells from VII, 5–10 µm in height, thinly covering gut. Intestine more or less widening in VII. Clusters of pear-shaped cells, 20–30 µm in height, present around ventral nerve cord in III–V. Transverse vessels forming loops in II–V.

All dorsal chaetal bundles, beginning in II, with hairs and crotchets. Hairs smooth, slightly sigmoid, about twice as long as crotchets in the same respective bundles; 5–8 per bundle, 150–172 µm long in anterior segments and 2–5 per bundle, 104–130 µm long in posterior segments. Dorsal crotchets ( Fig. 9A–C ) weakly sigmoid in shape with distal nodulus; 7–8 per bundle, 60–68 µm long in anterior segments, 2–5 per bundle, 50–64 µm long in posterior ones. Distal end of dorsal crotchets bifid or divided into several fine and blunt teeth. In some anterior bundles (mostly II and III), distal teeth frequently bifid ( Fig. 9E ) or pectinate with long lateral teeth and short intermediate teeth ( Fig. 9F ). In mid-segments, several (4–8) digitiform teeth arranged in a single row, showing pectinate condition ( Fig. 9G,H,L,M ). Distal teeth often rudimentary in posterior bundles ( Fig. 9I,J ). Ventral chaetae ( Fig. 9D ) all bifid crotchets with nodulus slightly distal to middle: 9–15 per bundle, 58–68 µm long in anterior segments and 2–10 per bundle, 50–60 µm long in posterior ones; upper tooth of the ventral crotchets about half as long as and slightly thinner than lower ones ( Fig. 9K ). No lateral expansion on dorsal or ventral crotchets. In sexually mature specimens, ventral chaetae in VII (segment having male pore) not modified but reduced in number or absent.

Clitellum from 1/2VI to end of VIII, conspicuous, broadly flattened ventrally; epidermis thick (up to 30 µm) and glandular. Gonads and copulatory organs ( Fig. 10A,B ) paired. Testes and ovaries paired respectively in VI and VII. Additional testes sometimes in V ( Fig. 10A ). Male funnels not large. Vasa deferentia about 260 µm long, not winding, connected with atria apically. Atria stoutly tubular in shape, 220 µm long, 80 µm wide, with high and glandular inner epithelium ( Fig. 10B,E ). Prostate gland large and solid, laterally connected to atrium by narrow (18 µm wide) junction ( Fig. 10F ). Ejaculatory ducts not detected. Penes rounded conical in shape, set in spacious copulatory bursa ( Fig. 10B ), opening ventrolaterally near middle of VII, immediately anterior to the chaetal bundle ( Fig. 10D ). Spermathecae in VI, opening ventrolaterally at mid-segment ( Fig. 10B, C ); ampullae large, globular or ovoid, 120–220 µm in diameter, containing 3–7 loose sperm masses; spermathecal ducts 30–50 µm long, short but well-defined from ampullae. Sperm sac in VI and VII. Egg sac in VII and VIII.

Remarks. Aulodrilus dentosus sp. nov. resembles A. pluriseta , A. japonicus or A. apeniatus in having hair chaetae beginning in II and pectinate chaetae in the dorsal bundles, but it is clearly distinguished from the congeners in having dorsal crotchets with multiple digitiform teeth of similar length and arranged in one direction. In contrast, distal ends of dorsal crotchets are bifid in A. pluriseta , with multiple upper teeth in A. japonicus , and with fine intermediate teeth between upper and lower teeth in A. apeniatus . As to the distal shape of the dorsal crotchets, the present species more closely resembles A. pectinatus . However, the present species has no modified genital chaetae. Its hair chaetae invariably begin in II, whereas A. pectinatus has spoon-shaped penial chaetae and lacks hair chaetae in II and III ( Aiyer 1928; Brinkhurst 1971). Furthermore, the number of distal teeth in dorsal crotchets of A. dentosus sp. nov. (5–8) is higher than that of A. pectinatus (usually 2–3 and rarely 4) ( Aiyer 1928). Structure of male duct of the present species resembles that of A. limnobius in the stoutly tubular atrium, which is slightly shorter than the vas deferens, and directly connected with penis without an ejaculatory duct.

Distribution. It has been recorded from muddy bottoms in shallow and eutrophic lakes and lagoons in Hokkaido, Honshu, and Okinawa islands in Japan ( Ohtaka 2014 under the name of Aulodrilus sp.). Aulodrilus sp. from Lake Hachiro-gata ( Ohtaka 2006), from Lake Izu-numa ( Ohtaka 2009), from Lake Kitaura ( Ohtaka & Kikuchi 1997), from Lake Toro ( Ito et al. 2002), from Lake Ogawara ( Ohtaka & Sato 2005), from Lake Takkobu ( Takamura et al. 2009), and from Lake Inaba-numa (Ohtaka et al. 2010) correspond to this species. The localities include both freshwater and brackish habitats. The present species can withstand salinity to some degree.

Figures

FIGURE 9. Chaetae of Aulodrilus dentosus sp. nov. from Lake Kitaura, Japan. A, dorsal crotchet in II; B and C, the same in mid-segments; D, ventral chaeta in IV; E and F, dorsal crotchets in anterior segments; G and H, the same in mid-segments; I and J, the same in posterior segments; K, ventral chaeta in an anterior segment; L and M, SEM photomicrographs of dorsal chaetae in mid-segments. E–K showing only distal ends.

FIGURE 10. Aulodrilus dentosus sp. nov. from Lake Kitaura, Japan. A, parasagittal section of anterior part of body; B, parasagittal section of genital segments; C, cross section at the level of spermathecal pores in VI; D, the same at the level of male pores in VII; E, longitudinal section of atrium and penis; F, cross section of atrium at the junction with prostate gland.