Daptonema sinica sp. nov.

LSID: urn:lsid:zoobank.org:act: A7115A5C-9CED-4EAE-8E00-468EF9A87C1B

(Figures 1–2, Table 1)

Holotype and paratype material. Four males and two females were obtained and measured. Holotype male on slide HDYST N88-11. Paratype 1 (male) on slide HDYST N54-2 - 3, paratype 2 (male) on slide HDYST N54-1 - 18, paratype 3 (male) on slide HDYST 1-12, paratype 4 (female) on slide HDYST N54-3 - 8 and paratype 5 (female) on slide HDYST N54-1 - 8.

Type locality and habitat. Holotype and paratypes were all collected from intertidal fine sandy sediments at Huangdao Silver Beach (120°12′3′′ E, 35°55′8′′ N) in May 2021.

Etymology. The species epithet refers to the country of origin, China.

Measurements. All measurement data are given in Table 1.

Description. Males. Body slender. Anterior end hemispherical with six spherical lips. Cuticle transversely striated. Somatic setae sparsely distributed throughout the body, 6–8 μm long. Inner labial sensilla papilliform. Outer labial setae and cephalic setae united in one circle and total 12 setae. Outer labial setae 6–8 μm long, cephalic setae 13–17 μm long or 87%–89% of the corresponding body diameter. Amphidial fovea circular, 8 μm in diameter, occupying 31%–35% of the corresponding body diameter, posterior to the buccal cavity (20–22 μm or 1.2 –1.5 head diameter from anterior end). Buccal cavity broad, funnel-shaped. Pharynx cylindrical, not enlarged at base. Cardia conical, 13 μm long, surrounded with intestinal tissue. Nerve ring at the middle of pharyngeal length. Ventral gland and excretory pore not observed. Tail conico-cylindrical with cylindrical posterior half and two terminal setae, 5.2–5.6 cloacal body diameters long. Three caudal glands well developed.

Reproductive system diorchic with two opposed testes. Spicules slender, bending into a hook shape in the posterior half, 28–29 μm long (about 1.2–1.4 times of the cloacal body diameter), proximal end cephalated and distal end pointed. Gubernaculum small and simple, plate-like, without apophysis, parallel to the distal end of spicules.

Females. Similar to males in morphologic characteristics, except tail relatively longer (c′=5.6–6.7 versus 5.2–5.6). Reproductive system monodelphic, ovary outstretched, located on left side of intestine. Vulva located at 70%–82% of total body length from anterior end. Post-vulval sac absent.

Differential diagnosis and discussion. Daptonema sinica sp. nov. is characterised by relatively large body with broad funnel-shaped buccal cavity; relatively long cephalic setae in the genus; circular amphidial fovea posterior to the buccal cavity, slender spicules bending into a hook shape in the posterior half; small and simple gubernaculum without apophysis; slender conico-cylindrical tail with two terminal setae.

In having similar spicules shape and gubernaculum without apophysis, the new species is simillar to D. fallax (Lorenzen, 1971) Lorenzen, 1977, D. microspiculum (Gerlach, 1953) Lorenzen, 1977 and D. oxycerca (de Man, 1888) Lorenzen, 1977. The new species differs from D. fallax by longer spicules (29 μm versus 19 μm), smaller amphidial fovea (31%–35% versus 80% of the corresponding body diameter) and shorter tail (c=9.5–12.8 versus 6.2–6.8). In addition, the latter species is characterized by a complex gubernaculum and numerous somatic setae. The new species differs from D. microspiculum by longer and slender body (1220–1583 μm long and a=43.6–48.0 versus 740–914 μm and a=24–31) and more anterior position of amphidial fovea (1.1–1.5 versus 2.5 head diameter from anterior end). The new species differs from D. oxycerca by relatively longer cephalic setae (13–19 μm versus 7–11 μm), shorter spicules without tooth distally (28–29 μm versus 57–83 μm), gubernaculum plate-like parallel to the distal end of spicules (versus tubular, surrounding distal end of spicules). D. sinica sp. nov. differs from its other congeners in the genus by combination of characters of broad funnel-shaped buccal cavity, relatively long cephalic setae (13–19 μm long), amphidial fovea posterior to buccal cavity, slender spicules bending into a hook shape in the posterior half, small and plate-like gubernaculum without apophysis and slender conico-cylindrical tail.