Aponema minutissima, Kovalyev, Shota V. & Miljutina, Maria A., 2009

Kovalyev, Shota V. & Miljutina, Maria A., 2009, A review of the genus Aponema Jensen, 1978 (Nematoda: Microlaimidae) with description of three new species, Zootaxa 2077, pp. 56-68 : 63

Aponema minutissima sp. n.

Table 1 , Fig 3 A–D, Fig 5 A

Type material. Holotype: male, slide No D–1/3.

Paratypes: 3 males, slides Nos from D-1/4-1 to D-1/4-3 and 5 females, slides Nos from D-1/4-4 to D-1/4- 8.

Locality. White Sea, Kandalaksha Bay, 66° 25’ N, 34° 22’ E. Depth 270 m. Collected on 27.07.1998. Other material collected on 15.10.1998, 31.05.1999, 24.11.1999.

Etymology. The name minutissima means “very small”.

Description. Body (fig. 3A) very small, fusiform, tapering to both ends, covered with numerous dorsolateral and ventrolateral somatic setae. Cuticle transversely striated. Cuticle striation clearly observed almost along total body. Head small, with a blunt anterior end. Amphidial fovea monospiral, almost round, large. Inner labial sensilla not found. Mouth opening surrounded by two visible crowns of sensorial organs: six setiform outer labial sensilla (length 1–1.5 μm) and four cephalic setae setae 1.5–2 μm long.

Buccal cavity small with larger dorsal (up to 0.3 μm long) and two minute ventrosublateral teeth. Pharynx (fig. 3B) divided into a thin, poorly-muscularized cylindrical anterior part and an almost spherical muscular bulb with lumen lined by sclerotized cuticle. Cardia small, barely discernible, triangular. Seven pairs of short somatic setae, each of 1.5–2 μm long, situated in the anterior body region. Nerve ring surrounds pharynx in its posterior part in front of bulb. Secretory-excretory pore located posterior the nerve ring, at 37 μm from the anterior end.

Single anterior testis lying left of intestine. Spermatogonia and spermatids large, 10–16 μm long, up to 8–10 μm wide. Spicules (fig. 3C) short, thin, curved, without differentiated capitulum. Gubernaculum not observed. Female reproductive system (fig. 3D) didelphic-amphidelphic, ovaries outstretched, oocytes large, with granular cytoplasm. Anterior ovary left of intestine, posterior one lying right of intestine. Vulval glands small, barely observable, filled with fine granules. One big spermatozoan (about 27 μm long and about 15 μm wide)) in uterus.

Tail relatively long, conical, with short (2–3 μm long) tube-like pointed tip. Three pairs of somatic setae (1.5–2 μm long) positioned dorsolaterally on the tail.

Diagnosis. Aponema minutissima sp. n. is characterized in both sexes by a very small body length within the genus, an absence of a cervical constriction and a very large amphidial fovea. Males without a gubernaculum.

Discussion. Aponema minutissima sp. n. mostly resembles A. nanum ( Blome, 1982) comb.n. and A. bathyalis sp. n. It differs from A. nanum ( Blome, 1982) comb. n. by having the amphidial fovea bigger than 50% of body diameter (versus 40%) and by the absence of a cervical constriction. From A. bathyalis sp. n. the new species differs in its smaller size, less annulated cuticle and absence of a gubernaculum.

Figures

FIGURE 3. Aponema minutissima sp. n.: A—total view of holotype male, B—pharyngeal region of holotype male, C—tail region of holotype male, D—female reproductive system. Scale: A— 50 μm, B, C, D— 20 μm.

FIGURE 5. Photomicrographs: A— A. minutissima sp. n., fragment of the testis of holotype male with large spermatozoa, B— A. westindicum sp. n., holotype male, C— A. bathyalis sp. n., copulatory apparatus of holotype male, D— A. westindicum sp. n., paratype female. Scale: A, C— 20 μm, B, D— 50 μm.