Ethmolaimus riparius, Gagarin, Vladimir G. & Naumova, Tatyana V., 2016

Gagarin, Vladimir G. & Naumova, Tatyana V., 2016, Ethmolaimus riparius sp. n. and Paramononchus major sp. n. (Nematoda) from Lake Baikal, Russia, Zootaxa 4098 (3), pp. 582-592 : 583-587

Ethmolaimus riparius sp. n.

( Fig. 1 , 2 ; Table 1 )

Type material. Holotype male, slide reference number 102/50, deposited in the museum collection of the Institute of Ecology and Evolution, Center for Parasitology, Russian Academy of Sciences (Moscow, Russia).

Paratypes. Seven males and ten females deposited in the collection of the Limnological Institute, Siberian Branch of the Russian Academy of Sciences (Irkutsk, Russia).

Type locality. Bolshie Koty Bay opposite the Limnological Institute Biological Station, Lake Baikal, Russia. Splash zone, about 50 cm above shoreline, sand. Collected on 25 June 2010.

Etymology. The specific epithet means ”riparian”, “living on the shore”.

Description. Male. Body long and comparatively thin, tapering toward both extremities. Cuticle with fine transverse striae and transverse rows of fine homogeneous punctations between transverse striae; lateral differentiation absent. Somatic setae numerous, thin and extremely long, 29–48 µm long. Head end truncate, corners rounded. Head continuous with adjacent body, lips amalgamated. Outer labial sensillae and inner labial sensillae papilliform. Four cephalic sensillae in the shape of long, thin setae 20–26 µm in length, 1.1–1.3 times as long as labial region width. Cheilostoma armed with 12 cuticularized ribs. Pharyngostom tubular with cuticularized walls, separated into two sections; anterior portion smaller and thicker than posterior portion. Three teeth placed at the junction of anterior and posterior sections of pharyngostom. Dorsal tooth slightly larger than both subventral teeth. Stoma length 1.3–1.5 labial region diameters, surrounded by longitudinal musculature. Amphidial fovea semi-spiral, 10–11 µm in diameter, located at the level of the posterior portion of stoma. Pharynx muscular, with well-developed basal bulb, measuring 32– 36 x 27–30 µm. Cardia conoid. Excretory pore located slightly posterior to nerve ring. Renette and renette canal not observed. Diorchic, testes opposed. Anterior testis situated to the left of intestine, posterior testis to the right. Spicules 1.4–1.6 times as long as the cloacal body diameter, robust, ventrally curved. Gubernaculum in the shape of an elongate plate, 21–25 µm long. Precloacal supplementary organs cuplike, 13–16 in number. Row of supplements is 200–295 µm long. Tail elongate-conical. Caudal setae numerous, 28–40 µm long. Three caudal glands present, opening through comparatively long, conical spinneret.

Female. General morphology is similar to that of males in the structure of cuticle and anterior body end. Cuticle with fine transverse striae and transverse rows of homogeneous punctations between transverse striae. Somatic setae numerous, thin and extremely long, 30–52 µm in length. Head continuous with adjacent body; lips amalgamated. Outer labial sensillae and inner labial sensillae paplliform. Four cephalic sensillae in the shape of long, thin setae, 1.1–1.3 times as long as labial region diameter. Cheilostom with 12 cuticularized ribs. Pharyngostoma tubular, divided into two sections. Dorsal tooth slightly larger than both subventral teeth. Stoma surrounded by longitudinal musculature. Amphidial fovea semi-spiral, 8–9 µm in diameter, located at the level of the of posterior stoma portion. Pharynx muscular, with well-developed basal bulb. Rectum 0.5–0.7 times as long as the anal body diameter. Reproductive system didelphic, amphidelphic. Anterior ovary situated to the left of intestine, posterior ovary to the right. Ovary flexures comparatively short; oocytes numerous. Vulva a transverse slit, situated slightly posterior to mid-body. Vulval lips sclerotized and protruding outside the body contour. Vagina short, straight, extending to one-fourth of the corresponding body diameter. Uterus spacious, containing two to five eggs, measuring 37– 44 x 32–40 µm. Tail elongate-conical, with caudal setae. Three caudal glands opening through conical spinneret.

Diagnosis. Body 1259–1501 µm long in males, 1228–1415 µm long in females. Somatic setae numerous, thin and extremely long. Its length is equal or slightly more than corresponding body diameter. Outer labial sensillae and inner labial sensillae papilliform. Four cephalic sensillae in the shape of thin setae, 1.1–1.3 times as long as labial region diameter. Pharyngostom separated into two sections. Three teeth located at the junction of these sections, dorsal tooth slightly longer than subdorsal teeth. Amphidial fovea semi-spiral, located at the level of posterior portion of stoma. Uterus spacious, containing two to five eggs measuring 36– 44 x 32–40 µm. Spicules comparatively long, ventrally curved. Precloacal supplements cup-like, 13–16 in number.

Character Holotype male Paratype males (n = 7) Paratype females (n = 10) range mean range mean L 1500 1259–1501 1384 1228–1415 1363 a 32 29–34 32 26–30

28

b 7.9 7.1–7.9 7.5 6.7–7.5 7.2 c 11.5 9.9–12.1 11.1 9.3–11.2 10.0 c' 3.6 3.6–4.3 3.9 3.4–4.7 4.1 V, % – – – 53.3–56.0 54.7 body diameter at the level of cephalic setae 21 19–22 21 19–22 21 mid-body diameter 47 39–52 43 44–57 50 anal or cloacal body diameter 36 30–36 32 29–40 34 length of cephalic setae (third ring) 25 20–25 23 21–25 22 length of cephalic setae divided by labial region diameter 1.2 1.1–1.3 1.2 1.2–1.4 1.3 stoma length 30 26–32 29 26–32 29 length of the stoma divided by labial region diameter 1.4 1.3–1.5 1.4 1.3–1.6 1.4 width of the amphidial fovea 11 10–11 10 8–9 9 distance from the cephalic apex to the anterior rim of the amphid 12 10–11 12 12–16 13 distance from the cephalic apex to the excretory pore 130 117–150 132 100–145 126 pharyngeal length 190 175–310 185 180–210 190 distance from the pharynx base to the cloaca 1180 975–1180 1073 – – distance from the pharynx base to the vulva – – – 525–580 556 distance from the vulva to the anus – – – 445–510 480 length of the rectum – – – 15–25 22 spicula length along the arc 50 45–50 47 – – gubernaculum length 24 21–25 23 – – number of supplements 15 13–16 15 – – length of supplement row 230 200–295 236 – – stoma length 130 110–138 126 125–145 137

Differential diagnosis. Ethmolaimus riparius sp. n. is one of the largest species of the genus ( Gagarin & Naumova 2012c). It is close to E. pilosus Shoshin, 1998 and E. lanatus Shoshin, 1998 in the presence of numerous and extremely long somatic setae, but differs from the first species in the longer and thinner body (L = 1228–1501 µm, a = 26–34 vs L = 720–1070 µm, a = 19–23 in E. pilosus ), longer stoma (26–32 µm long vs 19–24 µm long in E. pilosus ) and longer spicules and gubernaculum (45–50 µm and 21–25 µm long, respectively vs 32–37 µm and 8 µm long in E. pilosus ) ( Shoshin 1998). From E. lanatus new species differs in the longer body (L = 1228–1501 µm vs L = 680–1180 µm in E. lanatus ), relatively shorter cephalic setae (1.1–1.4 labial region diameters in length vs 1.6–2.1 labial region diameters in E. lanatus ) and longer spicules and gubernaculum (45–50 µm and 21–25 µm long, respectively vs 25–30 µm and 7–8 µm, long in E. lanatus ) ( Shoshin 1998).

Discussion. Species of the genus Ethmolaimus live in fresh and brackish waters, and in moist soil. At present the genus Ethmolaimus de Man, 1880 includes 13–17 valid species ( Andrássy 2005, Tchesunov 2014, Vanaverbeke et al. 2016, Boxshall et al. 2016).

Eight species have been recorded from freshwater habitats ( Decraemer & Smol 2005): E. derisorius Shoshin, 1998 , E. intermedius Jensen, 1994 , E. lanatus Shoshin, 1998 , E. maximus Gagarin & Naumova, 2012 , E.

parapratensis Alekseev & Naumova in Alekseev, Naumova & Dymina, 1979, E. pilosus Shoshin, 1998 , E. pratensis de Man, 1880, and E. zullini Eyualem & Coomans, 1996 . From this list, we consider only 6 of these as valid species; we consider E. intermedius , described from the Kiel Bight of the Baltic Sea, to be a synonym of E. hirsutus ( Gerlach, 1956) Jensen, 1994 because it differs only by a somewhat larger dorsal tooth.

E. caudatus Alekseev & Naumova, 1979 in Alekseev, Naumova & Dymina, 1979 we return to the rank of valid species, because it differs from the closely related E. parapratensis in three morphological characteristics: body size, tail length and position of the vulva.

Six Ethmolaimus species are found in Lake Baikal: E. pratensis , E. derisorius , E. lanatus , E. pilosus , E. maximus , and E. riparius sp. n. The final list of freshwater Ethmolaimus includes 9 valid species.

A key for identification of valid species of the genus Ethmolaimus from freshwater bodies is given below.

Figures

FIGURE 1. Ethmolaimus riparius sp. n. Holotype male and paratype female. A: male, entire body; B: male head; C: vulva region; D: female tail; E: male tail. Scale bars: A— 800 µm; B – E— 20 µm.

FIGURE 2. Ethmolaimus riparius sp. n. Holotype male and paratype female. A: male, entire body; B: female, entire body; C: male, anterior body end; D, E: male head; F: female head; G: vulva region; H: male, posterior body end; I: cloaca region; J, K: female tail. Scale bars: A, B— 100; C, H— 50 µm; G, I – K— 20 µm; D – F— 10 µm.

Tables

TABLE 1. Morphometrics of Ethmolaimus riparius sp. n. (all measurements are given in µm, except for the ratios a, b, c, c', V; length of cephalic setae divided by labial region diameter; length of the stoma divided by labial region diameter; number of supplements).

Character	Holotype male	Paratype males (n = 7)		Paratype females (n = 10)
		range	mean	range	mean
L	1500	1259–1501	1384	1228–1415	1363
a	32	29–34	32	26–30 28	28
b	7.9	7.1–7.9	7.5	6.7–7.5 7.2	7.2
c	11.5	9.9–12.1	11.1	9.3–11.2	10.0
c'	3.6	3.6–4.3	3.9	3.4–4.7 4.1	4.1
V, %	–	–	–	53.3–56.0	54.7
body diameter at the level of cephalic setae	21	19–22	21	19–22 21	21
mid-body diameter	47	39–52	43	44–57 50	50
anal or cloacal body diameter	36	30–36	32	29–40 34	34
length of cephalic setae (third ring)	25	20–25	23	21–25 22	22
length of cephalic setae divided by labial region diameter	1.2	1.1–1.3	1.2	1.2–1.4 1.3	1.3
stoma length	30	26–32	29	26–32 29	29
length of the stoma divided by labial region diameter	1.4	1.3–1.5	1.4	1.3–1.6 1.4	1.4
width of the amphidial fovea	11	10–11	10	8–9 9	9
distance from the cephalic apex to the anterior rim of the amphid	12	10–11	12	12–16 13	13
distance from the cephalic apex to the excretory pore	130	117–150	132	100–145 126	126
pharyngeal length	190	175–310	185	180–210 190	190
distance from the pharynx base to the cloaca	1180	975–1180	1073	– –	–
distance from the pharynx base to the vulva	–	–	–	525–580 556	556
distance from the vulva to the anus	–	–	–	445–510 480	480
length of the rectum	–	–	–	15–25 22	22
spicula length along the arc	50	45–50	47	– –	–
gubernaculum length	24	21–25	23	– –	–
number of supplements	15	13–16	15	– –	–
length of supplement row	230	200–295	236	– –	–
stoma length	130	110–138	126	125–145 137	137