Quisarctus yasumurai Fujimoto, 2015, sp. nov.

Quisarctus yasumurai sp. nov.

(Figs. 1, 2; Table 1)

Diagnosis. Halechiniscidae with cylindrical body; primary clava and lateral cirrus arise from common cirrophore; primary clava longer than lateral cirrus; secondary clava undeveloped; stylet supports present; leg I sense organ consists of three parts; leg II sense organ as unarticulated spine; leg III sense organ as unarticulated spine; leg IV sense organ as elongate papilla with distal spine; all legs terminate in four digits without folds, peduncles, proximal pads, pretarsi or wrinkles; internal digits longer than external digits; each digit terminates in sheathed, small, crescent-shaped claw with minute calcar; pair of ventrally opening seminal receptacles each with slender, sinuous duct terminating in spherical vesicle.

Material examined. Holotype: KUZ Z1649, adult female. Paratypes: KUZ Z1650, adult female; KUZ Z1651, four-digit juvenile.

Type locality: Water depth of 29 m, ‘Daidokutsu’ cave, off Iejima, Okinawa Islands, Ryukyu Islands, Japan (26°43'18"N, 127°50'00"E). Coll. by Koshin Yasumura on 6th November 2013.

Type depository: The type series is deposited in the Zoological Collection of Kyoto University.

Description of holotype (Figs. 1, 2 A, 2B). Adult female, body length 106 µm. Cylindrical body with smooth cuticle. Round cephalic region without lobes. Complete set of three parted cephalic cirri present. Dorsal median cirrus with scapus (2 µm), tubular portion (7 µm) and flagellum (3 µm) inserted 13 µm posterior to anterior margin of body. Dorsal internal cirrus with scapus (2 µm), tubular portion (5 µm) and flagellum (4 µm) inserted on short cirrophore. Ventral external cirrus with scapus (4 µm), tubular portion (4 µm) and flagellum (2 µm) slightly exterior to internal cirrus. Internal cirri and external cirri situated near anterior margin of body. Lateral cirrus with scapus (3 µm), tubular portion (5 µm) and flagellum (4 µm) inserted on short lateral cirrophorus with primary clava. Elongated, proximally-inflated primary clava (27 µm) with distal pore. Lateral cirrus situated antero-dorsal to primary clava. Secondary clava undeveloped. Mouth directed anteriorly. Observation of bucco-pharyngeal apparatus incomplete due to limited visibility in mounting media. Bucco-pharyngeal apparatus with buccal tube (21 µm), three placoids, pharyngeal bulb (11 µm × 11 µm) and two stylets (furca not observed). Stylet supports present but not observed in holotype. Cirrus E (20 µm) with proximal portion, distal portion and tapering spine inserted on short cirrophore. Leg I sense organ (5 µm) articulated into three parts. Leg II and III sense organs (8 µm, 7 µm) as unarticulated spines. Leg IV sense organ (5 µm) with proximal papilla and short, distal tapering. Each leg terminates in four digits without folds, peduncles, proximal pads, pretarsi or wrinkles. Internal digits longer than external digits. Digits on leg IV longer than that of legs I–III. Each digit terminates in sheathed, small, crescent-shaped claw without dorsal spur. Minute calcar recognised in well-positioned claws of internal and external digits. Rossette-like female gonopore opens 5 µm anterior to caudal anus. Pair of seminal receptacles present. Slender, sinuous seminal receptacle duct opens ventrally near lateral margin of body slightly posterior to level of gonopore and runs exteriorly and then dorsally terminating in spherical vesicle. In holotype, seminal vesicle directed dorsally gives spherical appearance.

Remarks on paratypes. In the paratypic female, KUZ Z1650, the digits were in better position for observation (Figs. 2 C, D). In addition, the stylet supports were more obvious (Fig. 2 E) and the seminal vesicles were observed from lateral view (Fig. 2 F). The other paratype, KUZ Z1651, was identified as a four-digit juvenile based on difficultly in observing the gonopore region and absence of both seminal receptacles and spermatozoa.

Etymology. The specific epithet, yasumurai, is named in honor of Koshin Yasumura who collected the sediment samples from which the new species was obtained.