Cirrodrilus homodontus (Yamaguchi, 1932)

Ohtaka, Akifumi, Konno, Tomoaki & Gelder, Stuart R., 2024, Taxonomic Revision of Cirrodrilus makinoi (Annelida: Clitellata: Branchiobdellida) with a Redescription of C. homodontus, Species Diversity 29 (1), pp. 43-51 : 47-49

Cirrodrilus homodontus ( Yamaguchi, 1932b) [Japanese name: Hoso-zariganimimizu ( Yamaguchi 1935a)] ( Fig. 5 )

Cambarincola homodonta Yamaguchi, 1932b: 454, fig. 1.

Stephanodrilus (Stephanodrilus) homodontus : Yamaguchi 1934: 200; Yamaguchi 1935a: 24, fig. 12-1; Yamaguchi 1935b: 13, fig. 3–5.

Stephanodrilus homodontus : Yamaguchi 1954: 101.

Cirrodrilus homodontus : Timm 1991: 329, fig. 46; Gelder 1996: 658; Gelder and Ohtaka 2002: 338; Ohtaka 2010: 460, fig. 12C; Gelder 2019: 489; Ohtaka et al. 2020: 180; Ohtaka et al. 2023: 29, fig. 4G.

Type material. Yamaguchi (1932b) did not designate any type specimens but stated C. homodontus were collected from Soranuma, Hokkaido, Japan ( No. 10 in Fig. 1 ), which by definition becomes the type locality. Later, Yamaguchi (1934) reported the species from Soranume, Hattaribetsu , Shimofurano , Makomanai , Muroran and Shintoku, Hokkaido (Nos 10, 11, 12, 3, 4, and 5, respectively). Seven whole-mounted specimens were identified as C . homodontus in the ICHUM collection ( Gelder and Ohtaka 2002), but as the slides were unlabeled and catalogue information is believed lost, their actual origin remains unknown. However , it is likely that at least some are syntypes but in the absence of firm data, the specimens were deemed to be potential syntypes by Ohtaka et al. (2020).

Material examined. ICHUM-1837–1840, 1842, 1845, 1846, are all potential syntype specimens of C. homodontus . ICHUM-8597–8600 , four whole-mounted specimens from Jōzankei, Sapporo and one each from Samani ( ICHUM-8601 ) and Esashi ( ICHUM-8602 ): locations, dates and collector are the same as those given for the C . makinoi specimens described above. Four whole-mounted specimens from Wakkanai , Hokkaido (45.43°N, 141.66°E), 19 October 2020, coll. T. Konno. One whole-mounted specimen from Yagishiri Island , Hokkaido (44.43°N, 141.41°E), 28 August 2002, coll. T. Kawai. Four whole-mounted specimens from Kaminokuni , Hokkaido (41.70°N, 140.27°E), 20 August 2017, coll. A. Ohtaka . All the specimens were removed from Ca . japonicus.

Description. Body cylindrical, 2.0 to 2.5 mm long alive, 1.0–1.5 long mm preserved ( Fig. 5A ). Body widest in segment 6, gradually narrower toward both anterior and posterior ends. Dorsal segmental appendage absent. Anterior pair of nephridial pores opening closely to the mid-line on the dorsal surface of segment 3. Head slightly narrower than segment 1 and as broad as posterior attachment disc. Peristomium distinctly shorter than head, and almost as long as segment 1. Peristomium with four tentacles on dorsal lip, each short and same length ( Fig. 5B ). Lateral tentacles two pairs, slightly shorter than dorsal tentacles. Ventral lip with a slight median emargination. Dorsal and ventral jaws similar in shape and size, 21.0–29.0 µm wide across the base, each with large medial tooth on the anterior margin and four pairs of small lateral teeth on anterior surface ( Fig. 5E, F ); dental formula 9/9 (4-1-4/4-1-4). Small lateral teeth pointed with angular ridges parallel to the median axes ( Fig. 5G ); the median pair of small teeth are similar ( Fig. 5E ) or smaller ( Fig. 5F ). Most male reproductive organs located in segment 6 ( Fig. 5H ). Glandular atrium tubular and folded, ental quarter dilated, total length 1.5–2.2 times segment diameter. Muscular atrium tubular, as thick as ectal part of glandular atrium, length about 0.3–0.4 segment diameter. Bursa ovoid, length about quarter segment diameter. Spermatheca in segment 5 ( Fig. 5H ), length 1.5 times segment diameter, consisted of small ovoid spermathecal bulb, without ental process and tubular duct with quarter of thinner ectal part.

Variations. Peristomial tentacles in preserved specimens often become swollen or shortened and difficult to distinguish ( Fig. 5C, D ); often as a result of preservation and mounting conditions. The jaw width in 13 specimens, including Yamaguchi’s voucher and our newly collected ones ranged from 21.0 µm to 29.0 µm (N = 25, mean value 25.4 µm). The dental formula of 9/9 (4-1-4/4-1-4) varies slightly with two jaws having five small teeth on one side and three on the other side of the large median tooth, e.g., 5-1-3.

Distribution. Widely distributed across Hokkaido Island (open symbols in Fig. 1 ).

Host. Cambaroides japonicus (De Haan, 1841) , the “Japanese crayfish” or “Nihon-zarigani” in Japanese.

Habitat. Specimens have been observed alive on all parts of the exposed host’s surface.

Figures

Fig. 5. Cirrodrilus homodontus. A, Lateral view of a whole specimen, Yamaguchi (1932b: fig. 1A) was redrawn; B, ventral view of peristomium, a whole-mounted specimen from Wakkanai, Hokkaido; C, the same from Yagishiri Island, Hokkaido; D, the same from ICHUM- 1845; E, anterior view of jaw in a whole-mounted specimen from Esashi, Hokkaido; F, the same from Kaminokuni, Hokkaido; G, lateral view of the dorsal jaw in ICHUM-1839; H, lateral view of segment 5 (left) with the spermatheca and male genitalia in segment 6 (right), a wholemounted specimen from Wakkanai. Abbreviations: b, bursa; ga, glandular atrium; ma, muscular atrium; mt, median tooth; sb, spermathecal bulb; sd, spermathecal duct; st, small tooth.Scale bars: A, H, 100µm; B–D, 50µm; E–G, 10µm.

Fig. 1. Localities of Cirrodrilus makinoi (solid symbols) and C. homodontus (open symbols). Solid triangles, Yamaguchi’s (1934) records under the name of Stephanodrilus (S.) makinoi; solid discs, records under the name of C. tsugarensis in Gelder and Ohtaka (2000) for No. 6, and in Ohtaka et al. (2023) for No. 7; solid squares, locations of C. makinoi in the present study. Open star, location of Yamaguchi’s (1932b) specimens under the name of Cambarincola homodontus; open triangles, locations of Yamaguchi’s (1934) specimens under the name of S. (S.) homodontus; open circles, locations of C. homodontus in Ohtaka et al. (2023). 1, Oshamanbe; 2, Muroran; 3, Shimofurano; 4, Rubeshibe; 5, Shintoku; 6, Imabetsu; 7, Jōzankei, Sapporo; 8, Esashi; 9, Samani; 10, Soranuma; 11, Hattaribetsu;12, Sōya Cape; 13, Wakkanai; 14, Toikanbetsu; 15, Ōnuma; 16, Enbetsu, 17, Yagishiri Is.; 18, Teuri Is.; 19, Tomamae; 20, Sōunkyo; 21, Hamamasu; 22, Yoichi; 23, Otaru; 24, Kyōgoku; 25, Suttu; 26, Shimamaki; 27, Kuromatsunai; 28, Shikabe; 29, Hakodate; 30, Kaminokuni.