Aulodrilus penicillatus Ohtaka, 2024, sp. nov.
Creators: name: Ohtaka, Akifumi
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Annelida
Clitellata
Tubificida
Naididae
Aulodrilus
Aulodrilus penicillatus

description: Aulodrilus penicillatus sp. nov.
(Figures 1–3)
Holotype. NSMT-An 1923, a whole-mounted mature and complete specimen, 30 May 2004, coll. S. Shinoda. Anterior part of body was partly broken.
Type locality. A stream fed by phreatic water in the Hakenomori Art Museum, Koganei City, Tokyo Prefecture, Japan (35.6949°N, 139.5130°E), with gravelly bottom.
Paratypes. NSMT- An 1924, a whole-mounted immature specimen; locality, date and collector the same as for the holotype. NSMT- An 1925, a whole-mounted immature specimen from a stream fed by phreatic water in the Yagawa Ryokuchi, Tachikawa City, Tokyo Prefecture, Japan (35.6870°N, 139.4240°E), with gravelly bottom, 2 December 2004, coll. S. Shinoda. All incomplete posteriorly.
Other material examined. A whole-mounted immature and incomplete specimen from a spring, Shira-Shimizu, Kawasaki City, Kanagawa Prefecture, Japan (35.6289°N, 139.5206°E), with gravelly bottom, 28 February 2006, coll. S. Shinoda.
Etymology. The specific epithet refers to the structure of the distal ends of chaetae, having tufts of fine bristles.
Diagnosis. Body stout, 26 mm long in preserved state. Posterior end not forming chaetaless or unsegmented region. Both dorsal and ventral chaetal bundles consisting of 8–12 crotchets in anterior segments, 4–6 crotchets in posterior segments. Distal end of chaetae sharply or bluntly simple-pointed in some to several anterior segments; those with tuffs of fine bristles in middle and posterior segments. No modified genital chaetae. Vasa deferentia not winding. Atria tubular with long ejaculatory ducts. Male pores in XI ventrally, spermathecal pores in X laterally.
Description. In preserved state, body stout, 26 mm long, 0.5–0.8 mm wide at anterior part of body (Fig. 1A), with 96 segments (holotype). Posterior end not forming chaetaless or unsegmented region (Fig. 1B). Prostomium bluntly conical, length less than half the width of segment I. No distinct secondary annulation. Body smooth, without any pigments. Epidermis 15–25 μm thick. Pharynx in II–1/2 IV, dorsal wall thicker than ventral wall, covered with pharyngeal glands dorsally. Chloragogen cells from VI on, thinly covering gut. Wall of gut 25–40 μm thick, without stomachal dilatation. Transverse blood vessels forming loops in I–XII. Dorsal vessel located ventrally in the middle parts of the body; it returns dorsally in the posterior segments (Fig. 1B). Body covered with thin and soft mucus with mingling foreign matter.
Chaetae all sigmoid crotchets with nodulus at 1/3 from distal end; form, size and number not different between dorsal and ventral bundles. Those in anterior segments slightly longer than in the following ones, 8–12 per bundle, 100–128 µm long (Fig. 2 A, D, F); those in middle segments 6–9 per bundle, 80–104 µm long (Fig. 2H); those in posterior segments 4–6 per bundle, 72–88 µm long, more strongly curved than those in preceding segments (Fig. 2K). Distal ends of chaetae in some anterior segments (II–III to II–V) sharply or bluntly simple-pointed (Fig. 2B, C); those in subsequent segments (V–X) with few (up to ten) short and fine hair-like bristles, replacing the upper tooth (Fig. 2E, G), chaetae from XI on with dozens of fine bristles in tufts (Fig. 2 I, J, L). No lateral expansions on the shafts of any chaetae. In mature worm number of ventral chaetae in XI reduced to four or five per bundles. No modified genital chaetae.
Clitellum inconspicuous, from beginning of X to end of XII, glandular epidermis 25–35 µm thick. Gonads and copulatory organs paired (Fig. 3). Testes and ovaries attached to posterior faces of septa 9/10 and 10/11, respectively. Vasa deferentia more than 300 µm long and 15–20 µm wide, not winding, connected to apical end of atria. Atria tubular, 250 µm long, 80 µm in maximum width, inner epithelia thick and glandular. Prostate glands about as large as atria, connected to atria through short and narrow stalks. Ejaculatory ducts 120 μm long, 15–30 µm wide, swollen at middle. Penes short and conical, opening at just lateral side of ventral chaetal bundles in XI. Spermathecae in X, small; ampullae elongately ovoid, 80 µm long and 50 µm in maximum width; ducts well-marked off from the ampullae, about 40 µm long, 30 µm wide, opening laterally in X. There is not sperm in the spermathecal ampullae.
Distribution and habitat. The present species was collected from a spring and two streams fed by phreatic waters, all with sandy or gravelly bottoms in Tokyo and Kanagawa Prefectures in central Japan. Water temperature of the habitats ranged from 11.1 to 18.4°C. Other oligochaetes, Lumbriculus mukoensis Yamaguchi, 1953 (Lumbriculidae) and Rhyacodrilus sp. (Naididae) were collected together with the present species.
Remarks. The holotype is the only sexually mature specimen available in the present study, but some reproductive organs such as male funnel and vas deferens could not be reconstructed due to destroyed condition.
Aulodrilus penicillatus sp. nov. resembles A. americanus Brinkhurst & Cook, 1966, which has been recorded from North America (Brinkhurst & Cook 1966; Brinkhurst 1967, 1978; Hiltunen 1967, 1969; Stimpson et al. 1975; Spencer 1980) and Japan (Ohtaka 2021), in lacking hair chaetae in the dorsal bundles and in having fine bristles on the crotchets in middle and posterior segments. However, detailed structure of the distal ends of chaetae is different in these two species. In A. americanus, up to ten palmate bristles are arranged sagittally, and they are gradually decreasing in size from lower to upper (Ohtaka 2021: Fig. 4B). On the other hand, in A. penicillatus sp. nov., each chaeta has a tuft of non-palmate fine hair-like bristles, replacing the upper tooth. In addition, the atrium is tubular with a distinct ejaculatory duct in A. penicillatus sp. nov., while the atrium is bean-shaped and almost devoid of an ejaculatory duct in A. americanus (Ohtaka 2021). These differences, however, may be due to the apparent lack of complete sexual maturity in the single specimen of the new species—the holotype —where sexual organs were developed. Small spermathecae opening laterally in Aulodrilus penicillatus sp. nov. resemble those in A. americanus (Ohtaka 2021: Fig. 3G). As to the distal shape of the crotchets, A. penicillatus sp. nov. more closely resembles A. japonicus Yamaguchi, 1953 in that both species have irregularly arranged multiple bristles. Aulodrilus japoniucs and A. penicillatus sp. nov. are also similar in having lateral openings of the spermathecae, tubular atria, and long ejaculatory ducts swollen in the middle. However, the multiple bristles of A. japonicus (Ohtaka 2021: Figs. 6D, E, G, H) are restricted to dorsal crotchets, and they are up to 20 in number and spine-like, being fewer in number and thicker than the multiple ‘capillaries’ in A. penicillatus sp. nov. Aulodrilus japonicus is also clearly different from A. penicillatus sp. nov. in having hair chaetae in the dorsal bundles. The pattern of change in the distal ends of the chaetae from anterior to posterior segments suggests that tufts of bristles on the chaetae in middle and posterior segments in the present species are originated from upper teeth.
description: Published as part of Ohtaka, Akifumi, 2024, Three new tubificine species (Annelida: Clitellata: Naididae) from Japan, pp. 186-200 in Zootaxa 5529 (1) on pages 187-189, DOI: 10.11646/zootaxa.5529.1.10, http://zenodo.org/record/14021730