Benthimermis tchesunovi, Miljutin, 2004

Miljutin, Dmitrij M., 2004, New findings of deep-sea nematodes of genus Benthimermis Petter, 1980 (Nematoda, Benthimermithidae) with description of seven new species, Zoosystema 26 (1), pp. 21-48 : 40

Benthimermis tchesunovi n. sp.

( Fig. 12 )

TYPE MATERIAL. — Holotype: Southeastern Atlantic , cruise WALWIS, stn DS 01, 33°53.9’S, 05°05.9’E, 5205 m, 24.XII.1978, mature ( MNHN 362 BF).

ETYMOLOGY. — In honour of Dr A. V. Tchesunov, Department of Invertebrate Zoology, Faculty of Biology, Moscow State University.

DIAGNOSIS. — The female of B. tchesunovi n. sp. is similar to B. australis and B. hureaui in shape of the tail. The new species differs from B. australis in the body length (1953 vs 4380-9400 µm), presence of a cuticular thickening at the cephalic apex, number of trophosomal cells at the cross-section (2-4 vs about 10 [ Chesunov 1988]), absence of the distinct uterus, and smaller and oval eggs (15 × 9 vs 30 × 30 µm). The new species differs from B. hureaui in the body length (1953 vs 2500-3800 µm), presence of the cuticular thickening at the cephalic apex, the body thickness (“a” = 38.3 vs 25.0-32.4), the thick cuticular walls of the vagina, and smaller and oval eggs (15 × 9 vs 25 × 25 µm). The new species is similar to B. minuta in its body length, but differs from B. minuta by the shape of the tail (conical vs rounded).

DESCRIPTION

Measurements: L = 1953 µm; “a” = 38.3; “c” = 55.8; “V” = 52.0%. Maximal body diameter = 51 µm. Diameter at level of: cephalic sensilla = 16 µm; amphids = 35 µm; midbody = 51 µm; anus = 37 µm. Distance from anterior end to amphid = 36 µm. Maximal size of eggs 15 × 9 µm. Body cylindrical, slightly narrowed to anterior end. Anterior end in shape of a rounded cone. Posterior end conical and angular. Amphidial apertures pore-like, about 1.5 µm in diameter. Four mediolateral cephalic setae about 1 mm long inserted in small pits. Mouth opening absent. The pharynx devoid of an internal lumen and looking like a shapeless cellular agglomeration. Midgut being a trophosome without visible internal lumen and consisting of two rows of big cells at level of midbody. Generally, dorsoventrally oriented pair of cells alternates with laterally oriented pair of cells. Trophosome consists of only one row of cells at posterior and anterior ends. Rectum resembling a short tube with thin walls. Anus present. Cuticle width about 1.5 µm at midbody, slightly increasing up to 4 µm at anterior end and up to 6 µm at posterior end. Apical cap-like cuticular thickening of 6 µm present at cephalic apex. Female reproductive system amphidelphic, occupying about one third of entire body length. Ovaries reflected. The oviducts long, about 200 µm. Vagina short. Thickness of vaginal walls comparable with thickness of body cuticle. No distinct uterus. Neither morphologically differentiated spermatheca nor spermatozoa nor vulvar glands observed.

Figures

FIG. 12. — Benthimermis tchesunovi n. sp., holotype (MNHN 362 BF); A, total view; B, cephalic end; C, tail; D, part of the tropho- some at the midbody; E, reproductive system. Abbreviations: a, amphid; o, oocytes or eggs; od, oviduct; ov, ovary; t, trophosome. Scale bars: A, 400 µm; B-D, 50 µm; E, 100 µm.