(Figure 3, A–G)
Type material: Holotype male (ref # M 1 / 9), one paratype male (ref # M 1 / 10) and four paratype females (ref # M 1 / 11, M 1 / 12, M 1 / 13, M 1 / 14) mounted in glycerin on glass slides. Type specimens are deposited in the collection of the P. P. Shirshov Institute for Oceanology, Russian Academy of Sciences, Moscow..
Type locality: The White Sea, Kandalaksha Bay, Station CBB 20 (1 A 1), RV KARTESH, 66 ° 23.47 ’ N, 34 ° 18.71 ’ W, depth 270 m, 27.07. 1998.
Etymology: Marisalbi (Latin) means "of the White Sea".
Morphometric data: Table 4.
......continued on the next page Description: Body elongate fusiform. Cuticle thin, finely annulated, without any lateral field. Ψ 3 with light brownish cuticle and hypodermis with brown pigment granules; bodies of other specimens seem neither brownish nor yellowish. Cephalic end anterior to the amphidial fovea very slightly narrowed in some specimens. Inner labial sensilla hardly visible. Cephalic crown of sensilla in males and females consists of six pairs of moderatesized setae (6 outer labial setae + 4 cephalic setae + 2 additional lateral setae). In the lateral pair, a ventral seta slightly shorter than the dorsal seta. Amphidial fovea large, slightly longitudinally oval or even rounded, with distinct cuticular rim and slightly asymmetrical central spot. No cervical setae. Short somatic setae scarcely distributed along the body. Buccal cavity very small and consisting mainly of a cheilostoma and an esophastoma reduced to a flat bottom. Esophagus slender, cylindroid, gradually widening to the cardia, with even radial muscular striation along its length. Cardia internal. No indications of a renette cell. Ovary of Ψ 1 and Ψ 3 situated entirely to the left side of the intestine. In Ψ 2 and Ψ 4, anterior portion of the ovary placed to the left of the intestine while posterior half portion bent to the right of the intestine. Uterus filled with small rounded spermatozoa. No postvulvar spermatheca. There are two (?) postvulvar glands with granular content. Anterior testis situated to the left of the intestine; posterior testis not seen. Spicules small but very distinct and robust, abruptly bent in the middle. Distal ends acute, proximal ends cephalated. Gubernaculum indistinct, as a rodlike body at the spicule distal ends. Tail with proximal conical and a distal slender cylindrical portions gradually going over in one another. Tail tip slightly widened with two or three very short subventral and subdorsal setae. There are two caudal gland cell bodies discernible within the tail. There are several pairs of pre and postanal lateroventral setae on the tail region.
Diagnosis: Body length 535–870 µm. Outer labial and cephalic setae 3.5 –5.0 µm long. Amphidial fovea 6–10 µm long; ratio length to width of the amphidial fovea 1.1–1.3; distance from cephalic apex to anterior rim of the amphidial fovea 7.0– 8.5 µm. Spicules 15–16 µm long. Terminal caudal setae 2.0–3.0 µm long.
Differential diagnosis: Amphimonhystera marisalbi sp. n. is similar to A. galea in general appearance and structural characters but differs by a very small or hardly visible inner labial sensilla, fewer of setae in the cephalic crown (12 versus 20) and by a number of morphometric characters such as shorter setae of the cephalic crown (3.5 –5.0 µm versus 7–15 µm) and tail terminal setae (2.0–3.0 µm versus 6.0–9.0 µm).