Enchodelus makarovae, Elshishka, Milka, Lazarova, Stela & Peneva, Vlada K., 2012

Elshishka, Milka, Lazarova, Stela & Peneva, Vlada K., 2012, Studies of the genus Enchodelus Thorne, 1939 (Nematoda, Nordiidae) from Arctic polar deserts. 1. Species with long odontostyle: E. makarovae sp. n. and E. groenlandicus (Ditlevsen, 1927) Thorne, 1939, with an identification key to the species of the E. macrodorus group, ZooKeys 212, pp. 1-23 : 2-6

Enchodelus makarovae sp. n. Figs 16

Material examined.

Eight females, six males and two first stage juveniles collected from Bol’shevik Island, Severnaya Zemlya Archipelago, Russian Arctic (Table 1).

Measurements.

See Table 2.

Description.

Female. Body slightly ventrally curved after fixation, rarely adopting an open C shape. Cuticle smooth when viewed under light microscopy, composed of several layers with optically different appearance. Cuticle 2-4 µm thick at postlabial region, 2-3 µm - at mid body and 8-11 µm on tail, posterior to anus. Subcuticle clearly striated. Lateral chord 6-9 µm wide, occupying10-12 % of mid body diam. Lip region with slightly angular appearance, offset by depression, 2.3-3.1 times as broad as high. Labial and cephalic papillae distinct. Amphid duplex, amphidial fovea cup-shaped, opening at level of depression. Cheilostom almost cylindrical with a narrower mid-section. Odontostyle 2.3-2.8 times longer than lip region diam. or 2.0-2.6% of total body length. Odontophore 1.2-1.4 times as long as odontostyle, with flanges. Guiding ring double, located at 1.4-2.0 lip region diam. from anterior end, collar (distance between the first and second guiding ring) 3 μm. Pharynx attains the full width at 65-70% of its length from anterior end. Pharyngeal expansion 113-130 µm long or 32-37% of total pharynx length. Pharyngeal characters are presented at Table 3. Nuclei of dorsal glands 4.5-5 μm diam. and ventrosublateral 1 μm and 3-4 μm of the first and second pair, respectively. Cardia small, rounded to elongate conoid. Genital system amphidelphic, both branches almost equally developed, anterior 264-310 µm, posterior 240-310 µm. Ovaries large, 206-218 µm long; oocytes first in two or more rows, then in one row. Oviduct 168-172 µm long, 2.1-2.4 times body diam., pars dilatata oviductus well developed. Sphincter between oviduct and uterus distinct. Uteri long, anterior and posterior uterus with almost equal length (267.6 ± 56.3 (220-346) μm, n=5 and 284.0 ± 25.5 (256-332) μm, n=6), or 2.9-4.9 times corresponding body diam. Uterus tripartite, consisting of a wider proximal portion with distinct lumen (146 μm, n=1), followed by a slender median portion (118, 112 μm, n=2) and ending with a well developed spheroid pars dilatata distalis uteri. Vagina extending inwards 27-42 μm or 38-59% of body diam., pars proximalis 24x26μm (n=1), pars refringens with two trapezoid sclerotisations, with a combined width of 20-21μm and length 6-8μm (n=2), pars distalis 5-7 μm, n=4. Two females with 3 and 4 uterine eggs, respectively, measuring 37-45 × 98-106 µm. Prerectum variable in length, 2.1-3.5 times the anal body width; rectum 0.6-1.1 anal body diam. long. Tail bluntly conoid with elongated saccate bodies present mostly along ventral side. Hyaline part of tail 8-12 µm thick or 24-47 % of total tail length. Two pairs of subterminal caudal pores, one subdorsal, another lateral.

Male. General morphology similar to that of the female, except for genital structures. Arrangement of pharyngeal gland nuclei is presented at Table 3. Lateral chord very narrow (4-6 μm) occupying10-12 % of mid body diam. with scattered glandular bodies. Reproductive system diorchic, composed of two opposed testes, anterior 311, 319 µm (n=2) and posterior 275, 285 µm (n=2) long. Sperm cells spindle-shaped, measuring 6-9 × 2 µm. Spicules dorylaimoid, 1.5-1.7 times anal diam. long, lateral accessory pieces paired, more or less cylindrical with bifurcate end, measuring 16-18 × 3 µm (n=2). Ventromedian supplements 10-12 in number preceded by one adcloacal pair of papillae located at 8-11 µm apart from cloacal opening, 0-1 in the range of spicules; moderately developed postcloacal papilla present. Prerectum 3.3-4.0 anal body diam. long. Tail bluntly conoid, ventrally almost straight, dorsally convex with broadly rounded terminus, two pair of caudal pores.

Juveniles. Two first stage juveniles were recovered. Body almost straight. Lip region flat, continuous with the body, genital primordium 11 μm long, tail conical with long central peg, 30, 33 μm long.

Diagnosis and relationships.

The new species Enchodelus makarovae sp. n. is an amphimictic species distinguished by females with body length of 1.57-2 mm, lip region 15-17.5 µm wide, amphid duplex, odontostyle 38-43 µm long or 2.3-2.8 times lip region diam. Odontophore with flanges, 1.2-1.4 times as long as odontostyle, pharynx length 320-377 µm, pharyngeal expansion 113-130 µm long or 32-37% of total pharynx length, female genital system amphidelphic, uterus tripartite, pars refringens vaginae with two trapezoid sclerotisations, vulva transverse slit, V=45-51%, tail rounded conoid (25-35 µm, c=45.8-70.3, c’=0.6– 0.9 in females, and 29-33 µm, c=46.4-58.9, c’=0.7– 0.8 in males). Males with 65-74 µm long spicules and 10-12 spaced ventromedian supplements.

Based on tail morphology and odontostyle length this species can be assigned to the Enchodelus macrodorus - group as defined by Guerrero et al. (2008). Thisgroup includes Enchodelus babakicus Pedram et al. 2009, Enchodelus carpaticus Ciobanu et al., 2010, Enchodelus distinctus Ahmad & Jairajpuri, 1980, Enchodelus groenlandicus (Ditlevsen, 1927) Thorne, 1939, Enchodelus macrodorus (de Man, 1880) Thorne, 1939, Enchodelus microdoroides Baqri & Jairajpuri, 1974 and Enchodelus saxifragae Popovici, 1995. This homogeneous group is characterised by the presence of a rather long odontostyle (>35µm), odontophore with well developed flanges, uterus tripartite (except for Enchodelus distinctus , which has been described with a bipartite uterus ( Ahmad and Jairajpuri 1980) and hemispheroid to rounded conoid tail.

In having a lip region set off by a depression the new species is most similar to Enchodelus carpaticus , Enchodelus groenlandicus , Enchodelus macrodorus and Enchodelus microdoroides . However, it can be separated from Enchodelus carpaticus by its shorter pharyngeal expansion (113-130 vs 136-167 µm), different arrangement of pharyngeal glands, DN and S2N situated more posteriorly (DN=69-72% vs DN=63-65%, S2N=86-89% vs SN=82-86 %, respectively), absence of dorsal cell mass near cardia vs presence, ovaries large (206-218 µm long) vs short (61-155 µm long), prerectum shorter (87-140 vs 164-272 μm or 2.1-3.5 vs 4.1-6.6 anal body diam), saccate bodies present vs absent, males abundant vs absent (in Enchodelus carpaticus males not found, but sperm cells were observed in one female from a Romanian population ( Ciobanu et al. 2010)); it should be mentioned also that there are differences in average values of odontostyle (av. 40.7 (38-43 µm) vs av. 43.3 (39.5-47 µm) and tail length (av. 29.2 (25-35) vs av. 23.7 (21-29) μm), and c’ value ( c’ = av. 0.7 (0.6-0.9) vs av. 0.6 (0.5-0.7); from Enchodelus groenlandicus by its shorter odontostyle (38-43 vs 44-53 µm), somewhat more anteriorly located guiding ring (24-28 vs 27-37 µm), narrower lip region (15-17.5 vs 19-22 µm), males present vs absent; from Enchodelus macrodorus this new species differs in having a longer ovarium and oviduct (206-218 vs 83-188 μm and 168-172 vs 97-159 μm, respectively ( Thorne’s specimens), longer uterus (220-346 vs 61-143 and 56-115 μm) and shorter prerectum (2.1-3.5 vs 3.9-5.8 anal body diam), tail somewhat longer (25-35 vs 18-24 and 22-28 μm) and differently shaped (bluntly conoid vs rounded to hemispherical), saccate bodies large elongated vs small round; males abundant vs males rare; longer tail in males (29-33 vs 18-22 μm, c=46.4-58.9 vs 67-100 and c’=0.7– 0.8 vs 0.6) ( Guerrero et al. 2007b, 2008); from Enchodelus microdoroides by its longer body in females (1.57-2 vs 0.94-1.29 mm), wider lip region (15-17.5 vs 13-14 µm),guiding ring located more anteriorly (24-28 vs 28-39 µm from anterior end), different shape of pars refringens vaginae (trapezoid vs rectangular), longer tail (25-35 vs 13-27 µm) and males with longer spicules (65-74 vs 45-50 µm).

The new species can be distinguished from the remaining three species of Enchodelus macrodorus group by its lip differentiation: lip region set off by depression vs offset by a distinct constriction. Further, it differs from Enchodelus babakicus by its longer body in female (1.57-2 vs 1.21-1.56 mm), ovaries longer (206-218 µm vs 39-63 µm), longer uterus (220-346 vs 130-175 μm) and tail (25-30 vs 16-22 μm); shorter prerectum (87-140 vs 151-232 μm or 2.1-3.5 vs 4.5-8.5 anal body diam. long), males with longer spicules (65-74 vs 49-61 µm) and narrower lateral chord (10-12 vs 15-20% of corresponding body diam.); different tail shape in first stage juvenile (straight vs ventrally curved); from Enchodelus distinctus the new species is differentiated by its longer odontostyle (38-43 vs 36 µm), more posteriorly located guiding ring (24-28 vs 21-23 µm), different structure of uterus (tripartite vs bipartite), saccate bodies present vs absent. Finally, the new species can be distinguished from Enchodelus saxifragae by a narrower lip region (15-17.5 vs 18-22 µm or 2.3-2.8 vs 1.8-2.3 odontostyle as lip region diam.), shorter pharyngeal expansion (av.121 (113-130) vs av.153 (144-162.5) and av. 147 (116-186) µm), shorter prerectum (87-140 vs 140-294 μm or 2.1-3.5 vs 4-8 anal body diam) and fewer ventromedian supplements (10-12 vs 13-16) ( Popovici 1995, Guerrero et al. 2008).

Type-locality and habitat.

Different types of vegetation from a polygonal polar desert on Bol’shevik Island, Severnaya Zemlya Archipelago, Russian Arctic (Table 1).

Type-material.

Holotype, 5 paratype females, 4 paratype males and 2 juveniles deposited in the Nematode collection of the Institute of Biodiversity and Ecosystem Research, BAS; one female and one male paratypes each at the nematode collections of the following institutions: The Center of Parasitology of Institute for Problems of Ecology and Evolution, RAS, Russia and Plant Protection Service, Wageningen, The Netherlands.

Etymology.

The species is named in honor of Dr. Olga Makarova (Institute for Problems of Ecology and Evolution, Russia) who is an outstanding biologist investigating polar habitats and has kindly provided us with numerous nematode materials from Arctic polar deserts.