Cirrodrilus iwakiensis, Ohtaka & Gelder, 2015

Ohtaka, Akifumi & Gelder, Stuart R., 2015, Description of a New Species of Branchiobdellida (Annelida: Clitellata) and Comparison with Other Cirrodrilus Species in Northern Honshu, Japan, Species Diversity 20, pp. 67-71 : 68-70

Cirrodrilus iwakiensis sp. nov.

[Japanese name: Iwaki-zarigani-mimizu] ( Figs 1A–E , 2 )

Material examined. Holotype: ZIHU 4930 removed from Cambaroides japonicus collected by A. Ohtaka, 22 September 2012 from Oku-Shirasawa Stream on northwestern slope of Mt. Iwaki , Ajigasawa village, Aomori Prefecture, Honshu Island, Japan (40°40′32″N, 140°15′29″E) . Paratypes: ZIHU 4931 , ZIHU 4932 , USNM 1251839 collected from same locality and host species as holotype by M . Mukohyama on 16 October 1997; ZIHU 4934 from same host species as holotype by A . Ohtaka, 9 September 1997 from Upper Uemata Stream , Imabetsu town . Additional non-type specimens from same host species: ZIHU 4933 (Tokiwano, Mt. Iwaki, by A. Ohtaka, 18 June 2013), USNM 1251840 , 1251841 ( Yayoi , Mt. Iwaki, Hirosaki city, by A. Ohtaka, 11 May 2014), and NBM 010306–010308 (from type locality, by A. Ohtaka and M. Mukohyama, 16 October 1997, 26 July 1998, and 14 August 1998, respectively) .

Diagnosis. Body slim and pyriform, 1.2–1.8 mm long fixed; head width equal to or less than width of segment 1; dorsal segmental ridges, supernumerary muscles, and dorsal or lateral appendages absent; two anterior nephridial pores widely separated on dorso-lateral surface; oral region cylindrical or funnel-shaped, surrounded by 15 dorso-lateral peristomial tentacles, alternating long (8) and short (7) with short one located at medial position, and with ventral lip medially incised and flanked by pair of small lateral lobes; 16 oral papillae present; jaws dissimilar, dorsal one larger with semi-circular base narrowing to wing-like lateral tips, large median tooth slightly curved anteriorly, and small teeth on anterior margin, ventral one with smaller, kidneyshaped base, large median tooth and small teeth on anterior margin, with dental formula of 10/10 (5-1-4/5-1-4); single, deep pharyngeal sulcus present; male organs small, glandular atrium club-shaped, length 0.3× segment diameter, deferent lobes absent; muscular atrium tubular, length 0.2× segment diameter, penial sheath in ectal half, bursa small and spherical, penis eversible; spermatheca reduced, spermathecal duct length 0.1× segment diameter, spermathecal bulb not recognized.

Etymology. Named after Mount Iwaki, on the slopes of which the type locality is located.

Description. Specimens 1.2–1.8 mm long, head with shallow sulcus behind peristomium; body slim and pyriform ( Fig. 1A ). Head width equal to or less than width of segment 1, about equal to diameter of posterior attachment disc. Dorsal segmental ridges, supernumerary muscles, and dorsal or lateral appendages absent. Anterior nephridial pores on segment 3 widely separated on its dorso-lateral surface. Oral region cylindrical or funnel-shaped, surround- ed by 15 peristomial tentacles and narrow ventral lip, latter medially incised with pair of lobes flanking it ( Fig. 1B ). Tentacles consisting of seven short (one being median) and eight long ones, alternating around dorsal and lateral margins of oral region ( Figs 1B , 2 ). Oral papillae 16 in number, surrounding mouth. Jaws dissimilar in size and shape ( Fig. 1C, D ). Dorsal jaw larger, having semi-circular base and tapering lateral wing-like tips, bearing large, slightly anteriorly curved median tooth and small, conical or rounded teeth across its anterior margin. Ventral jaw smaller, with oval or kidney-shaped base and both large median tooth and small teeth across its anterior margin. Dental formula 10/10 (5- 1-4/5-1-4). Single, deep sulcus extending around middle of pharynx.

Pair of testes located in segments 5 and 6 on anterior septal wall with stages from morulae to spermatozoa free within coelom in both segments. In each segment, two prominent sperm funnels each connect to a short, vas efferens which then merge into a vas deferens ( Fig. 1E ); both vasa deferentia enter the glandular atrium ectally. Male organs difficult to see, being small and often pressed against ventral body wall. Glandular atrium club-shaped, its length 0.3× segment diameter, without deferent lobes or prostate gland ( Fig. 1E ). Muscular atrium tubular, its length 0.2× segment diameter, with its ectal half forming a penial sheath and connected to small, spherical bursa containing eversible penis. Spermatheca with short duct, 0.1× segment diameter, passing through body wall before terminating shortly after ( Fig. 1E ). An anticipated ental glandular bulb has not be found to date.

Variations. The peristomium may be either cylindrical or funnel-shaped, and the body is slim-pyriform to rod-like. These variations reflect the worms’ reaction on contact with a preservative. Dental formulae range from 10/9 (5-1-4/4-1- 4) to 11/11 (5-1-5/5-1-5) and maybe greater; however, the respective jaw base shapes and sizes are all alike. The small, short spermatheca is rarely recognizable as it is pressed against the ventral body wall.

Distribution and habitat. The new species is found in the western half of Aomori Prefecture in northern Honshu ( Table 1).

Japanese crayfish were collected from small, cold, headwater streams with small rocks interspersed with patches of gravel and thin branches. Specimens of C. iwakiensis were not found in the branchial chamber, but on their hosts’ carapace, abdomen, and appendages, among which no preferential site can be discerned.

Host. Cambaroides japonicus .

Remarks. Specimens of Cirrodrilus iwakiensis always occurred with more numerous C. aomorensis on a host. Specimens were collected throughout the year except during January to March, when snow and ice prevented access to the collection sites. Examination of gut contents of C. iwakiensis showed no appreciable change in composition over the seasons. The diet consisted of brown, amorphous flocculent masses with diatom frustules, algal debris (cell walls), and mineral particles in small amounts. Occasionally, small bodies containing nucleated cells and larger unidentifiable fragments, also nucleated, were observed.

Figures

Fig. 1. Cirrodrilus iwakiensis sp. nov. A, Lateral view of paratype (ZIHU 4931); B, ventral view of peristomium of paratype (ZIHU 4932), median tentacle arrowed; C, jaws (dorsal over ventral), anterior view through mouth, paratype (ZIHU 4934); D, jaws (dorsal over ventral), lateral view (m = mouth) of holotype (ZIHU 4930); E, schematic lateral view of reproductive organs in segments 5 and 6 based on holotype (ZIHU 4930) and other material, showing only their ventral half (connecting duct in segment 5 was not observed), glandular atrium dotted; muscular atrium and spermathecal duct with tangential lines; bursa and spermathecal duct with longitudinal lines). Scale bars: A, 200µm; B, 100µm; C, D, 20µm; E, 50µm.

Fig. 2. Cirrodrilus iwakiensis sp. nov. Frontal view of oral region showing arrangement of peristomial tentacles and jaws located centrally. Scale bar: 100µm.