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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Labronema

Family Dorylaimidae (ref. ID; 6182, 7916)

ref. ID; 1663

Anterior portion of esophagus nearly as wide as posterior portion; total length usually more than 2 mm. Rare species. (ref. ID; 1663)
  1. Labronema loeffleri Andrassy, 1976 (ref. ID; 7916)
  2. Labronema macrosoma Alekseev, 1992 (ref. ID; 7916 original paper)
  3. Labronema magnum Altherr, 1972 (ref. ID; 7916)
  4. Labronema obesum Thorne, 1974 (ref. ID; 7916)
  5. Labronema rapax Thorne, 1974 (ref. ID; 7916)

Labronema macrosoma Alekseev, 1992 (ref. ID; 7916 original paper)

Diagnosis

The genus Labronema is a member of the Dorylaimidae (Alekseyev, 1988). The new species is close to species having an axial vulva: L. loeffleri Andrassy, 1976; L. magnum Altherr, 1972; L. obesum Thorne, 1974; L. rapax Thorne, 1974. It is closest to the first two. The new species differs from L. loeffleri in having a larger spear (56-61 vs. 52-57 µm), the guiding ring twice as long, the raio of the length of hindgut to the length of the tail twice as small (0.6-0.9 vs. 1.5-1.7 µm), in having a different shaped spicule, and shorter vagina. The species L. loeffleri is known only from a high-mountain lake in the Himalayas (Andrassy 1978). Our species differs from L. magnum in having a longer body (female 5.2-5.9 vs. 4.7-4.9 mm) spear extension (78-81 vs. 45 µm), in the smooth, and not finely annulated, cuticle, in the considerably longer guiding ring of the spear and shorter vagina. This species is described from the coastal sand of a water body in Sweden (Altherr 1972). The nematodes of the two other species of this group inhabit the soil, and, in addition, their length is about half that of the news species. Freshwater Labronema have not been previously recorded from the territory of the USSR (Eliava 1982). (ref. ID; 7916)

Descriptions

Large nematodes, body subcylindrical, weakly tapered anteriorly. Cuticle with distinct longitudinal lines, thick. Thickness of cuticle at the level of the lips 5-5.5 µm. Middle of the body 10-11 µm, and tip of the tail 9-10.5 µm. Lateral field constitutes one-fifth to one-sixth body diameter, In some specimens, it appears granular. The labial region is set off by a weak body constriction. The amphid is gobletlike, situated at the base of the lips; the diameter of its opening is 11-14 µm. Body diameter in females at the level of the lips is 32-36 µm, vulva 180-215 µm, anus 78-91 µm; in males at the same levels: 31-32 µm, 154-176 µm, and 70-72 µm. Length of the esophagus in females is 990-1012 µm, diameter at the guiding ring 17-24 µm, nerve ring 42-50 µm, cardia (esophago-intestinal valve) 70-90 µm; in males: 943-1010 µm, 20-25 µm, 31-35 µm, 66-73 µm, respectively. Male and female spear have identical shape and length, 59-62 µm (twice the head diameter), width in the middle 9. The guiding ring of the spear is paired, height 10-11 µm, spear extension 78-81 µm. Spear opening is less than one-third its length. In fourth instar larvae, the functional (larval) spear 43-44 µm, the spear extention 62-63 µm. Length of the forming (replacement or juvenile) spear 56-57 µm, that is, 1.3 times longer than the larval, width of spear 7. Spear extensions are absent. Midgut is very large filled with a homogenous mass. In two females, the posterior section of the midgut contained numerous spindlelike cells (most likely, microsporidia) 40-45 µm in length. Prerectum is more than 1.5 times longer than the hindgut the length of which is 70-84 µm. The distance from the cephalic end to the amphid is 8-10 µm, to the guiding ring 200-210 µm, and vulva 2240-2790 µm. The vulva-anus distance is 2120-3020 µm. Length of the anterior ovary is 740-770 µm, posterior 512-517 µm. Vulva is axial, length of opening 27-27 µm. The vagina is strongy muscular, its depth 63-70 µm, diameter 42-56 µm. Eggs are 130-215x53-58 µm, egg index 2.3-2.9. There are two testes. Spicules (125-127 µm) are without pronounced heads. There is no gubernaculum. Supplements 28-30 µm, tubular, occupy an are extending 122-130 µm. Distance from the end of this field to the cloaca is 120-127 µm. There are 12 pairs of submedial, 5-6 caudal papillae and 1 precloacal supplement. The tail is bluntly conical, its length 51-58 µm. (ref. ID; 7916)

Examined materials

Two males, five females, 3 juveniles. Holotype female NP-2549(3): body length=5210 µm, a=25.1, b=5.2, c=89, V=45 percent. Paratypes males (2 specimens): body length=4660-4750 µm, a=26-30, b=4-6, c=91-92.2. Paratypes females (4 specimens): body length=5440-5930 µm, a=26-30, b=5.2-6.3, c=85-90, V=44-47.5 percent. Middle course of the Frolovka River, depth around 1 m, coarse sand, July 1984. (ref. ID; 7916)

Type specimens

The specimens are deposited in the Department of Zoology of the Far East University. (ref. ID; 7916)