Benthimermis turpicauda, 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 : 42-44

Benthimermis turpicauda n. sp.

( Fig. 13 ; Tables 6; 7)

TYPE MATERIAL. — Holotype: mature; paratype: immature (see Tables 6 and 7 for details).

ETYMOLOGY. — From Latin turpis (ugly, deformed) and cauda (tail).

DIAGNOSIS. — Females of B. turpicauda n. sp. differ from all other species of Benthimermis in the irregular shape of their caudal terminal spine. The ovaries of the mature female B. turpicauda n. sp. are hologonic. The ovaries of such construction are only known in B. megala Petter, 1987 , the biggest known species of genus Benthimermis ( Miljutin & Tchesunov 2001) . The new species differs from B. megala in the body length (3.4 and 6.1 vs 65-170 mm), the structure of the trophosome (one row of big cell vs multicellular trophosome), the shape of the caudal terminal spine, and many other parameters.

DESCRIPTION

Measurements are presented in Table 7. Body cylindrical, slightly narrowed at anterior end. Anterior end in shape of rounded cone. Posterior end rounded, possessing terminal cuticular process of irregular shape. Amphids non-spiral. Amphidial apertures pore-like, about 4 µm in diameter. Four mediolateral cephalic setae about 4 µm long inserted in small pits. Small pores connected with hypodermal glands in sublateral chords. Mouth opening absent. Pharynx devoid of an internal lumen and terminated posteriorly by a shapeless cellular agglomeration. Trophosome consisting of one row of big cells. Peripheral cytoplasm of trophosomal cells light and without any inclusions, but middle parts of the trophosomal cells filled with numerous vesicles and granules. Generally, transversal circular ridges of hypodermis present around joining trophosomal cells. Rectum looking like a thinwalled tube. Anus subterminal and hardly seen.

r

Cuticle width about 5 µm at midbody, slightly increasing at terminal part of posterior end. Female reproductive system amphidelphic, very short. Ovaries short, hologonic (germinal zone extending throughout entire length of gonads). In mature female, oviducts short, twisted, very wide in their proximal parts, and containing eggs. No distinct uterus. Vagina is short, with thin cuticular walls. Neither morphologically differentiated spermatheca nor spermatozoa nor vulvar glands were observed.

REMARKS

The holotype and the paratype have been found in different parts of the world ocean very distant from each other. The paratype is almost twice longer than the holotype. However, these specimens are similar in body proportions, morphology of the trophosome, transversal circular ridges of the hypodermis around the places of the junction of the trophosomal cells, and, undoubtly, belong to the same species.

Morphology of the female reproductive system in B. turpicauda n. sp. (hologonic ovaries) is different from that of most other Benthimermis species. The ovaries of Benthimermis typically are telogonic (the germinal zone confined to the distal ends) ( Petter 1980, 1983 a, 1987; Chesunov 1988; Tchesunov 1988). Only one exception has been known before: the giant (up to 17 cm in length) species B. megala Petter, 1987 , having hologonic ovaries too ( Miljutin & Tchesunov 2001).

The caudal terminal spine of B. turpicauda is of variable and irregular shape and, evidently, is vestigial.

Figures

FIG. 13. — Benthimermis turpicauda n. sp.,; A, C-E, G, holotype (MNHN 317 BF); B, F, H, paratype (MNHN 333 BF); A, total view; B, total view; C, cephalic end; D, a part of the trophosome at the midbody; E, reproductive system; F, reproductive system; G, tail; H, tail. Abbreviations: a, amphid; l.ch, lateral hypodermal chord; l.-m.ch, lateromedian hypodermal chord; m, somatic musculature; o, oocytes or eggs;ov, ovary; ph, vestigial pharynx; r, rectum; t, trophosome. Scale bars: A, B, 500 µm; C, G, H, 50 µm; D-F, 100 µm.