Aponema bathyalis Kovalyev & Miljutina, 2009, sp. n.

Aponema bathyalis sp. n.

Table 1, Fig 2 A–D, Fig 5 C

Type material. Holotype: male, slide No D-1/14.

Paratypes: 4 males, slides Nos from D-1/15-1 to D-1/15-4, 5 females, slides Nos from D-1/15-5 to D-1/ 15-9.

Type locality. White Sea, Kandalaksha Bay, 66° 25’ N, 34° 22’ E. Depth 270 m. collected 27.07.1998. Other collections on 15.10.1998, 31.05.1999 and 24.11.1999.

Etymology. The name bathyalis means “from bathyal area of the sea”.

Description. Body slender, cylindrical in males (fig. 2D), more spindle-shaped in females. Cuticle seems to be almost smooth, transversely striated in the anterior part of the body and in tail region. Head 4.5–5.0 μm long, offset by a slight cervical constriction. Amphidial fovea monospiral, almost oval, 5.0–5.5 μm wide (63–83 % of corresponding body diameter) in males, 4–5 μm (50–71 % of c. b. d.) in females, with protruding corpus gelatum (fig. 2A), situated 9–12 μm from the front end in males, 8.5–15 μm in females. Oral opening surrounded by circle of six inconspicuous inner labial papillae (0.3–0.5 μm long). Outer labial sensilla and cephalic sensilla arranged in two separate circles located in a distance ca 3 μm from one another. Outer labial sensilla setiform, 1.0–1.5 μm long in both sexes. Third circle of four cephalic setae 2–3 μm long in males and 1.5–2 in females. Stoma small, cyathiform, 3–4 μm long, bearing small dorsal (ca 0.5 μm long) and two minute ventrosublateral teeth.

Pharynx consisting of thin cylindrical anterior part with poorly developed muscular elements and posterior oval muscular bulb with cytoplasmic interruptions. Cardia trapezoidal. Nerve ring just posterior to mid-pharynx. Ventral secretory-excretory pore situated at level of nerve ring. Anterior part of intestine displaced dorsally by ventral gland cell. Single anterior testis lying left of intestine. Spicules rather large, ventrally curved, cephalated, provided with a velum. Gubernaculum with largely rod-like blade, bent towards the extremities with pronounced hook proximally (fig. 2C). Four small papilliform medioventral supplements situated 1,5 μm, 11 μm, 28 μm and 42 μm respectively anterior of anus. Spermatids small, egg-shaped, 5 μm long. Ovaries paired, outstretched, lying ventrally of intestine. Oocytes large (30–35 μm long), with granulated cytoplasm (fig. 2B). Several spermia 7–12,5 μm long in uterus. Vulva located at 204–255 μm from anterior end of body. Tail conical, containing three caudal glands.

Diagnosis. Aponema bathyalis is characterized in both sexes by a short and thin body, short tail and wide amphidial fovea with protruding corpus gelatum. Males have 4 precloacal supplements, and a long and thin gubernaculum.

Discussion. Only three Aponema species are known to possess body lengths of less than 0.5 mm: A. nanum (Microlaimus nanus Blome, 1982, comb. n.), A. nympha and A. minutissima.

A. bathyalis sp. n. differs from A. nympha by the more posterior position of the amphidial fovea at about 1.5 head diameter from the anterior of the body vs at less than 0.7 of head diameter in A. nympha, and by a protruding corpus gelatum. A protruding corpus gelatum has also been observed in Bathynox clavata Bussau & Vopel, 1999, a genus which also possesses a single testis in male but differs from it by presence of somatic setae inserted on processes. A. bathyalis sp. n. also resembles A. nanum but this species has no protruding corpus gelatum, no gubernaculum and a longer tail (c = 5.8–7.8 versus c = 8.2–11.3). New species differs from A. minutissima by presence of gubernaculum and cervical construction.

a, b, c and c’).