Benthimermis improvisa, 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 : 32-34

Benthimermis improvisa n. sp.

( Fig. 6 )

TYPE MATERIAL. — Holotype: Western Atlantic , cruise DEMERABY, stn KG 27, 10°23.02’N, 46°45.08’W, 4800 m, 28.IX.1980, mature ( MNHN 332 BF).

ETYMOLOGY. — From Latin improvisus (surprising, unexpected).

DIAGNOSIS. — Described male differs from all other known males of Benthimermis by the shape of cephalic setae which are thin and acute; by the structure of the male reproductive system consisting of one long nonpaired terminal testis and gonoduct, while males of the other Benthimermis species possess two testes. Besides, this male has a round ventral gland at the level of amphid, which opens outside.

DESCRIPTION

Measurements: L = 4844 µm; “a” = 88.1; “c” = 92.3. Maximal body diameter = 55 µm. Diameter at level of: cephalic sensilla = 24 µm; amphids = 45 µm; midbody = 50 µm; anus = 45 µm. Distance from anterior end to amphid = 66 µm. Length of lateral cervical alae = 31 µm, maximal height of lateral cervical alae = 4 µm. Spicules 28 µm long. Body thread-like, cylindrical. Anterior end in shape of a rounded cone. Posterior end conical. Amphids non-spiral. Amphidial aperture round, about 4.5 µm in diameter. Amphidial fovea tubiform. Four very thin acute bristle-shaped mediolateral cephalic setae about 2.5-3.0 µm long. Cuticle width about 3.0 µm. Lateral cervical alae anterior to amphids. Their length about a half of distance from anterior end to amphids. Mouth opening absent. Pharynx looking like a non- muscular string devoid of an internal lumen with a thickening on posterior end. Small spherical gland at level of amphid on ventral side of the body, possessing a short canal ended by a distinct outlet 1.5 µm wide on ventral side. Midgut being a trophosome without visible internal lumen. Trophosome consisting of several rows of cells at posterior part of body. But in middle part of body, trophosome formed by a chain of rather large cells. Anus present. Male reproductive system about 3 mm long, consisting of one long non-paired terminal testis and long vas deferens. Spicules straight, distally acuted, without a gubernaculum. Nine midventral supplementary organs present anterior to anus.

REMARKS

The cephalic thin and acute setae are not found in any other species of Benthimermis . Setae of such shape may be considered as a primitive feature, which is peculiar to free-living nematodes. The ventral round gland at the cervical part of the body represents a vestigial renetta (excretory organ of free-living nematodes).

Benthimermis marionensis Petter, 1983 ( Fig. 7 )

Benthimermis marionensis Petter, 1983a: 9 , 10, fig. 5.—

Tchesunov 1988: 15-17, figs 3, 4.

TYPE MATERIAL. — Holotype: S part of Indian Ocean,

46°52.5’S, 37°53.5’E, 110 m, 25.III.1976, ( MNHN

166 BB); paratypes:same data, 6 ( MNHN 166 BB) .

MATERIAL EXAMINED. — Western Atlantic, cruise DE-

MERABY, stn KG 03, 8°7.88’N, 49°3.71’W, 4440 m

depth, 12.IX.1980, 1 immature ( MNHN 322 BF).

DESCRIPTION

Measurements: L = 9000 µm; “a” = 64.3; “V” = 53.5%. Maximal body diameter = 140 µm. Diameter at level of: cephalic sensilla = 33 µm; amphids = 86 µm; midbody = 140 µm. Distance from anterior end to amphid = 84 µm.

Body thread-like, cylindrical. Anterior end in shape of a rounded cone. Posterior end conical, possessing terminal spine 130 µm long. Core (apparently cytoplasmic) with granular inclusions inside terminal spine. Cuticle width is 3-6 µm. Mouth opening absent. Four mediolateral papilloid cephalic setae about 3.0 µm long insert- ed in tiny pits. Amphids non-spiral. Amphidial aperture pore-like. Amphidial fovea tubiform, slightly wider than aperture. Pharynx looking like a non-muscular string without an internal lumen. Midgut being a multicellular trophosome without visible internal lumen. Rectum and anus absent. Female reproductive system amphidelphic, occupying about one fifth of total body length. Ovaries reflected. Vagina short. Neither morphologically differentiated spermatheca nor spermatozoa nor vulvar glands discovered.

REMARKS

B. marionensis was described upon eight mature females from the southern part of the Indian Ocean, 46°52’S, 37°51’E, 31-110 m depth ( Petter 1983a). The other findings were made in the Southern Atlantic, 57°09’S, 26°09’W from depth 1729 m ( Tchesunov 1988). The new finding is from absolutely another region and a much greater depth. The new specimen agrees with the original description of B. marionensis in shape of the tail with the terminal spine possessing cytoplasmic core; construction of the gonad and the trophosome. Body length, the de Man “V” index, and the distance from the anterior end to the amphid are in accordance with the original description too (9.0 mm, 53.5%, and 84 µm vs 9.3-14.8 mm, 46.5-74.0%, and 70-85 µm respectively). However the terminal spine of the new specimen is twice shorter than in the original description (130 vs 200-320 µm). Besides, there is no evident anus in the new specimen contrary to type specimens ( Petter 1987). As the new specimen was found far from the place of the first finding, it is possible that it can belong to another population of B. marionensis . This suggestion can explain the size differences in several morphological features.

Figures

FIG. 6. — Benthimermis improvisa n. sp., holotype (MNHN 332 BF); A, total view; B-D, cephalic end; E, tail; F, part of the trophosome at the midbody; G, beginning of the testis; H, end of the testis. Abbreviations: a, amphid; gd, gonoduct; l.a, lateral alae; l.-m.ch, lateromedian hypodermal chord; m, somatic musculature; ph, vestigial pharynx; s, spicule; su.or, supplementary organ; t, trophosome; te, testis; v.ch, ventral chord; v.g, vulvar glands. Scale bars: A, 500 µm; B-E, 50 µm; F-H, 20 µm.

FIG. 7. — Benthimermis marionensis Petter, 1983,; A, total view; B, cephalic end; C, tail; D, region of vulva; E, body wall at the anterior end, laterally. Abbreviations: a, amphid; l.-m.ch, lateromedian hypodermal chord; m, somatic musculature; m.ch, median hypodermal chord; od, oviduct; ph, vestigial pharynx;t, trophosome; v, vulva; v.g, vulvar glands.Scale bars: A, 1000 µm; B-E,50 µm.