Eutobrilus

Order Enoplida (ref. ID; 7909)

Order Enoplida: Family Tobrilidae (ref. ID; 7912)

ref. ID; 7912

Within Eutobrilus, three species groups are well distinguished (Tsalolichin, 1983). The largest group is graciliformes, which includes, at the present time, thirteen valid species. Morphologically, they are very close to the species of Tobrilus; at least their females are not distinguishable. The medius group includes two species E. medius and E. vistula, their position in Eutobrilus is dubious. In the structure of the mouth apparatus (both pockets of the stoma are fused with the buccal cavity), E. vistula, probably, should be included in Paratrilobus. The structure of stoma of E. medius (the anterior pocket is fused with the buccal cavity) justifies the placement of this species in Epitobrilus. The grandipapillatus group includes 11 valid species. The unifying character of species in this group is the structure of the supplementary apparatus in males. This character has high taxonomic value (Paramonov 1962) and because of this, this species group should be elevated to generic rank. (ref. ID; 7912)

Eutobrilus angarensis Gagarin, 1991 (ref. ID; 7909 original paper)
Eutobrilus annetteae (Joubert & Heyns, 1979) Tsalolikhin, 1981 (ref. ID; 1311)
Eutobrilus arcticus Gagarin, 1991 (ref. ID; 7912 original paper)
Eutobrilus differtus Shoshin, 1988 (ref. ID; 7909)
Eutobrilus erbaevae Gagarin, 1991 (ref. ID; 7909 original paper)
Eutobrilus graciliformes (Altherr and Debouteville, 1972) (ref. ID; 7912)
Eutobrilus medius (ref. ID; 7912)
Eutobrilus prodigiosus Shoshin (1988) (ref. ID; 7912)
Eutobrilus strenuus Gagarin, 1991 (ref. ID; 7912 original paper)
Eutobrilus vistula (ref. ID; 7912)

Eutobrilus angarensis Gagarin, 1991 (ref. ID; 7909 original paper)

Diagnosis

This species is closest to Eutobrilus differtus Shoshin, 1988. Differs from it in the absence of the subterminal bristle on the tail, broader head and longer cephalic bristles (E. differtus: head width 20-25 µm, length of longer cephalic bristles 9-11 µm) and in having larger spicules in males (E. differtus: spic. 44). (ref. ID; 7909)

Descriptions

Nematodes of average size. Biocrystals in the majority of individuals absent in the body cavity, if they are present then only in small numbers in the region of the esophagus. Anterior end rounded: vestibulum relatively shallow. Head width in females 40-50 µm, in males 39-40 µm. Length of large cephalic bristles 17-20 µm which is 36-46 percent of head width, length of smaller cephalic bristles 10-14 µm. Buccal cavity goblet-like, its depth 15-17. Length of both pockets equal to or slightly greater than depth of the buccal cavity. Openings of the amphids situated approximately at the base of the buccal cavity. Mean length of the esophagus in males 437 µm, in females 519 µm. NR=28-30 percent. Females didelphic, gonads reflexed. Uterus muscular. In the uterus of sexually mature females, there are usually 5-8 synchronous eggs measuring 45-64x42-60 µm. Males have seven or eigth barely visible supplements. Supplements are small, distances between them not uniform. Greatest distance between the first three from the cloaca. The last from the cloaca are tightly packed. Overall length of the supplemental row 420-500 µm. Sicules relatively long and proportionate, with heads. Tail smoothly conical, its end club-shaped. Length of tail in females 18-255(222) µm, in males 135-152(144) µm. Caudal glands well developed. Subterminal bristle absent. (ref. ID; 7909)

Remarks

Species previously mentioned in the fauna of the Angara River as Tobrilus sp. (Gagarin and Yerbayeva, 1984). (ref. ID; 7909)

Examined materials

Three (male, male), 18 (female, female) from the middle course of the Angara River, 500 m above the mouth of the Vikhorevaya River, depth 3 m, sand, 19.VI.1973. Holotype (male) (preparation M-101), L=2303 µm, a=22.80, b=5.26, c=15.15, c'=2.53, spic. 56, suppl. 8. Paratypes: 18 (female, female), L=2264-3446(2847) µm, a=21.09-30.41(24.88), b=4.91-6.23(5.49), c=10.06-15.28(12.84), V=38.81-46.70(43.46) percent, c'=3.38-5.15(4.06); 2 (male, male), L=2138 and 2404 µm, a=20.36 and 25.31, b=4.75 and 5.68, c=15.84 and 16.47, c'=2.57 and 2.55, spic. 60, 62, suppl. 7, 8. (ref. ID; 7909)

Type specimens

Type specimens are deposited in the collection of the Laboratory of Biology and Systematics of Aquatic Organisms of the USSR Academy of Sciences Institute of Inland Waters Biology (Borok village). (ref. ID; 7909)

Eutobrilus annetteae (Joubert & Heyns, 1979) Tsalolikhin, 1981 (ref. ID; 1311)

Descriptions

Body posture upon fixation variable, from almost straight to completely ventrally curved. Cuticle 2 µm (1-3 µm) thick, finely transversely striated, with somatic setae occurring all over the body. Around ten somatic setae in the pharyngeal region, fourteen between cardia and anus, and two on the tail observed on the left side of one specimen. First somatic seta situated slightly less than one and one half lip region width from the anterior end. Sensilla in two circlets. An inner whorl of six labial papillae and four short cephalic setae. Labial setae one-third of lip region width long, while cephalic setae are one-fifth lip region width long. Amphidial aperture transverse oval, with funnel-shaped fovea immediately followed by the fusus amphidialis, situated near posterior end of stoma. Lips fused and continuous with the rest of the body. Stoma cup-like and one and one-half times longer than wide, with well sclerotized wall, a small dorsal tooth-like projection followed by two overlapping ventro-sublateral tooth pouches. The first ventro-sublateral tooth is situated 17 µm (16-18 µm) from the anterior end, the second 3.4 µm (3-4 µm) behind the first. Pharynx cylindrical, muscular, followed by a triangular cardia which itself is surrounded by three glandular structures. Nerve ring surrounds pharynx anterior to middle. Intestine with wide lumen terminating in a rectum that is slightly longer than one anal body width. Tail tapering anteriorly but becomes more cylindrical posteriorly; tip slightly ventrally curved. There is no subterminal seta. Three caudal glands arranged in tandem and opening through a tubular spinnertet. Female reproductive system didelphic, amphidelphic with reflexed ovaries. The junction between oviduct and uterus unclear. Vaginal muscles weakly developed. Vulva transverse, situated anterior to middle of body. Eggs 48x35 µm, 57x22 µm, 48x37 µm and 50x35 µm, shell excluded and 57x24 µm, 55x24 µm, 49x37 µm, 63x27 µm and 52x37 µm with shell. (ref. ID; 1311)

Male: Male not found. (ref. ID; 1311)

Measurements

Body length 1294+/-101(1160-1480) µm, maximum body width 47+/-3.1(43-51) µm, pharyngeal length measured from the anterior end 270+/-13.6(247-289) µm, tail length 197+/-14.1(179-228) µm, anal body width 21+/-1.8(20-26) µm, lip region width 24+/-1.0(23-26) µm, outer labial seta length 7+/-0.7(6-8) µm, cephalic seta length 5+/-0.4 (4-5) µm, stoma length 13+/-0.7(13-15) µm, stoma width 9+/-0.8(8-10) µm, first tooth anterior body end 17+/-0.7(16-18), second tooth anterior body end 21+/-0.9(19-22) µm, cuticle thickness 2+/-0.5(2-3) µm, nerve ring from the anterior end 100+/-3.8(95-107) µm, egg length 53+/-4.3(49-57) µm, egg width 24+/-5.3(24-37) µm. (ref. ID; 1311)

Eutobrilus arcticus Gagarin, 1991 (ref. ID; 7912 original paper)

Diagnosis

The species is close to E. graciliformes (Altherr and Debouteville, 1972) described only from males from a river in the northern USA. The new species differs from E. graciliformes in its longer head setae (in E. graciliformes, length of longest head setae is only 33-35 percent of the width of the head). (ref. ID; 7912)

Descriptions

Nematodes of medium size, males distinctly smaller than females. Cuticle thin ringed, somatic setae sparse, short. Biocrystals in the body cavity absent. Head blunt, width of head 45-60 µm. Length of large head setae in females 27-33 µm (55-60 percent of head width), in males 24-27 µm; length of shorter head setae 12-16 µm. Vestibulum high; buccal cavity goblet shape, 12-14 µm wide, 15-18 µm deep. Pockets of stoma distinct, overlapping, onchia large. Openings of amfids positioned at level of base of buccal cavity. Cordial glands large. Supplements 6-9 µm, more often 7 µm. Supplements urchinlike, size 11-15x11-13 µm. Distances between supplements unequal. Maximal distance between cloaca and first supplement and between first and second supplements; minimal distance between second supplement and cloaca. Spicules thick, curved, mean length 47 µm (44-53). Tail long, slender. Caudal glands and spinneret well developed; subterminal seta on tail absent. (ref. ID; 7912)

Examined materials

Eight (female, female), 7 (male, male), and 10 juveniles in flowing brook near Lake Taimyr, Logata, 28.VII.1988. Holotype (male) (preparation "Taimyr-3"): L=1880 µm, a=34.78, b=4.38, c=13.91, c'=3.60, spic. - 45, suppl. - 8. (ref. ID; 7912)

Type specimens

Type specimens are deposited in the collection of the Laboratory of Biology and Systematics of Aquatic Invertebrates of the Institute of Biology of Inland Water Bodies of the Academy of Sicences of the USSR, Borsk. (ref. ID; 7912)

Eutobrilus erbaevae Gagarin, 1991 (ref. ID; 7909 original paper)

Diagnosis

Differs from all other species in having unusually long cephalic bristles. As a rule, the length of the larger cephalic bristles in all known species does not exceed 50-60 percent head width. (ref. ID; 7909)

Discriptions

Proportionate nematodes of average size. Cuticle with distinct small annularity; somatic bristles numerous. Cephalic end blunt; vestibulum comparatively shallow. Head width in males 28-31 µm, in the female 34 µm. Cephalic bristles thick, long; length of larger cephalic bristles in males 21-24 µm, which is equal to 70-80 percent of head width, in females 21 (62 percent head width) µm. Length of smaller cephalic bristles 11-13 µm. Width of buccal cavity 10-14 µm; depth 10-12 µm. Depth of both pockets approximately equal to depth of buccal cavity. Overall depth of stoma 22-24 µm. Openings of amphids situated at the level of the middle of the buccal cavity or slightly below. Mean length of esophagus in males 445 µm, in female 510 µm. Cardiac glands are well developed, rounded. NR=28-33 percent. Males have six supplements with well-developed hangers and a movable cap. They are arranged in two groups: two supplements close to the cloaca (size 19-23 µm), a zero-supplement, two supllements measuring 20-23 µm, and a last one measuring 8x9 µm. Overall length of the supplemental row 270-416 µm. Spicules are slender, weakly arched. The proximal end is wide, triangular; apical end is divided. The gubernaculum bears a dorsal apophysis. The tail in both sexes is proportionate, smoothly conical. Its mean length in males is 171 µm, in the female 251 µm. Caudal glands are well developed. There is a subterminal bristle. (ref. ID; 7909)

Remarks

Previously mentioned in the fauna of the Angara River as Tobrilus anguiculus Tsalolichin, 1977 (Gagarin and Yerbayeva 1982, 1984). (ref. ID; 7909)

Examined materials

Four (male, male), one (female) from the middle course of the Angara River (depth 0.5 m, ground-cobble, sand, above the mouth of the Vikhorevaya River, 9.VIII.1976). Holotype (male) (preparation M-305, 2 st.), L=2210 µm, a=31.13, b=4.7, c=13.64, c'=3.60, spic. 65, suppl. 6. Paratypes: 3 (male, male), L=2174-2311(2224) µm, a=25.68-33.66(29.84), b=4.97-5.21(5.07), c=11.96-14.49(12.91), c'=4.00-5.55(4.73); spic. 60-64, suppl. 6; (female) L=2481 µm, a=28.85, b=4.86, c=9.88, V=48.97 percent, c'=6.19. (ref. ID; 7909)

Type specimens

Eutobrilus strenuus Gagarin, 1991 (ref. ID; 7912 original paper)

Diagnosis

It is similar to E. prodigiosus Shoshin (1988), differs in the smaller body size and head setae (in E. prodigiosus, head setae are longer, 35-40 percent of the head width). (ref. ID; 7912)

Descriptions

Body slender. Cuticle thin, rings poorly expressed. Biocrystals in body cavity present. Somatic setae sparse, 2.5-3.0 long. Width of area of lips 24-27 µm. Lips tall, vestibulum huge. Buccal cavity small: depth 9-10 µm, width 8-9 µm. Rings of head setae close. Head setae of the first circle powerful, long, their diameter at base 4-4.5 µm (50-55 percent of head diameter). Setae of second circle shorter and thinner, their length 8-10 µm. Pockets of stoma poorly expressed, onchia small. Openings of amfids positioned at level of lower part of buccal cavity. Cordial glands well developed, rounded, 20-30 µm in diameter. Width of body in area of vulva 80-100 µm. Females didelphic, ovaries curved. Vulva equatorial. Vagina relatively short; walls of uterus rather muscular. Egg size 60-70x45-54 µm. Tail slender, its length 3.5-4.6 times the body diameter at anus. Terminus slightly swollen, subterminal seta present. In their guts, diatom algae were observed. (ref. ID; 7912)

Examined materials

Thirty-two (female, female) and 8 juveniles found in Lake Taimyr, VIII.1988 (depth 10-13 m, substrate-silt). Holotype (female) (preparation "Taimyr-36"): L=1547 µm, a=20.63, b=6.31, c=9.38, V=41.82 percent, c'=4.58. (ref. ID; 7912)