Mesomermis devii, Gorgadze & Received & Online & Version, 2017

Gorgadze, Oleg, Received, Shalva Barjadze, Online, Published & Version, Final, 2017, Mesomermis devii sp. nov. (Nematoda: Mermithidae), a new species of nematode from Devi Cave in Georgia, Turkish Journal of Zoology 41 (3), pp. 408-415 : 410-413

publication ID	https://doi.org/ 10.3906/zoo-1603-17
persistent identifier	https://treatment.plazi.org/id/313B87AB-0139-FF98-FD0A-35FAFBFAFAAB
treatment provided by	Felipe
scientific name	Mesomermis devii
status	sp. nov.

Treatment

Mesomermis devii View in CoL sp. nov. ( Figures 1 View Figure 1 and 2 View Figure 2 )

Type locality: Georgia: Samegrelo– Zemo Svaneti region , Tsalenjikha district , near Chkvaleri village , Kvira karst massif, Devi (Demish–pokva) Cave (42°44′N, 42°5′E, alt. 1121 m a.s.l.) GoogleMaps .

Type material: holotype (adult female) on slide: dark zone, Devi Cave , 24 October 2012 (code CAU –Devi– 20121024–01) . Paratypes (same data as holotype): 4 adult females on 3 different slides, the same data as for holotype ( CAU –Devi–20121024–02–05); male is not known . Holotype and paratypes are deposited in the collection of the museum of the Institute of Zoology of Ilia State University, Georgia .

Measurements. Holotype (adult female): length = 14.1 mm; head diameter at the level of cephalic papillae = 45 µm; body diameter at the level of nerve ring = 85 µm; maximum body diameter = 160 µm; distance head to nerve ring = 260 µm; length of amphid = 9 µm, its width = 8 µm V = 52%; length of vagina = 115 µm; diameter of vagina in the frontal part = 40 µm; in the middle part = 25 µm; in the terminal part = 22 µm.

Paratypes (adult females; n = 4): length = 13.6 (13.1– 14.1) mm; a = 80–86; b = 5.2–5.5; V = 52%–59%. Head diameter at the level of papillae 41 (38–45) µm; length of amphids = 9 (9–10) µm, width = 8 (7–8) µm; body diameter at the nerve ring = 87 (85–88) µm; maximum body diameter = 156 (152–160) µm; body diameter at the level of vulva = 156 (153–160) µm; distance from the head to nerve ring = 257 (260–254) µm; V = 55.9% (52.2%–59.7%); length of vagina = 116 (115–117) µm; diameter of vagina in the frontal part = 41 (40–42) µm, in the middle part = 25.5 (25–26) µm, and in the terminal part = 22.5 (22–23) µm.

Morphology. Adult female (n = 5): the nematode is small in size, with white coloration. Frontal part of the body is significantly narrowed ( Figures 1a View Figure 1 and 2a View Figure 2 ). Apical part of the head is rounded and symmetrical ( Figures 1b View Figure 1 and 2b View Figure 2 ). Head diameter is four times less than that of the body. Collar not narrowed at the end. Stomal aperture is located in the middle of the apical part of the head, sometimes slightly displaced to the ventral side. Amphids are small in size, with large holes. Papillae are situated close to amphids. Terminal part of the body is conic at the tail and significantly narrowed. Tail is rounded at the end and slightly bent at ventral side ( Figures 1e View Figure 1 , 2c, and 2d View Figure 2 ). Terminal part of the tail without mucron.

Cuticle is thick, with smooth surface; cross fibers are not visible. Cuticle thickness varies depending on the fixing agent ( TAF and lactophenol). For example, thickness of stomal longitudinal cuticle of the nematode, fixed in TAF, is 12 µm; near the nerve ring = 10.5 (10–11) µm; in the middle of the body = 10 (11–12) µm; near the tail terminus = 14 µm. With fixing in lactophenol, the same indices were equal to 15, 13, 15, and 17 µm, respectively. Dorsal and ventral longitudinal cords are well developed ( Figure 1d View Figure 1 ). Along with the dorsal and ventral cords, nematodes have 2 lateral and 2 subdorsal cords. Dorsal and ventral cord cells are located at the front of the nerve ring, arranged in 2 and 3 rows. Behind the nerve, along the entire dorsal side of the body, one row of cells is significantly narrowed; 2 rows are narrowed in the central part as well. Cells of the terminal (caudal) part of the body are larger than in the central part. Lateral cords are the best developed. Cells in the front of the nerve ring cells are arranged in 3–4 rows; above the nerve ring, in 2–3 rows ( Figure 1a View Figure 1 ); and behind the nerve ring to the end of the stichosoma, in 3 rows. Here they occupy 1/3 of the body length; lateral cords are the widest in the midbody, and in the terminal part of the body, lateral cords pass to the dorsal side and make up the cells of the 4th row. The 6 papillae are located on the head at a single level; they are remote from each other; each dorsolateral papilla is equipped with 2 sensilla; the rest, with 3 sensilla (papillae have a total of 16 sensilla). Amphids are small in size, roundish-oval in shape ( Figures 1b View Figure 1 and 2b View Figure 2 ). They are located behind the lateral papillae, slightly dorsally, 30 µm from the frontal end of the head. The hole of the amphid is large; its diameter (7.5 µm) is nearly equal to the width of the amphid. Amphids have large (12.5 × 13 µm) pouches (pockets). Excretory hole is located behind the nerve ring. It is located 257 µm from the apical end of the body at the transverse section of 87–88 µm diameter. The 4 dorsal holes of the cervical (neck), postpapillar glands, and 5 ventral openings of the postpapillar glands are presented. The 4 dorsal and 4 ventral openings of the postpapillar glands are arranged parallel to each other in front of the nerve ring, and there is one opening on the ventral side, behind the nerve ring. The first anterior pair of postpapillar glands has its openings behind the capitular papillae (at the level of amphidial hole); the second and third pairs are located close to each other and are 120 and 130 µm respectively from the apical end of the head. The fourth pair is located after the nerve ring, 280–290 µm from the apical end of the head. The pharyngeal tube ends before the middle part of the body. Its total length is 3.5 mm, constituting 15% of the entire body length. The diameter of the pharyngeal tube is different at different parts of the body. For example, the length of the pharyngeal tube in the stoma is 25 µm ( Figure 1b View Figure 1 ), 12 µm of which passes through the head cuticle (its diameter is 2.5 µm), and 13 µm of which extends out of the cuticle to the amphids. Walls of tube channel are thick, wide, chitinized, and uneven in shape. In this section of the stoma, the diameter of the pharyngeal tube is 5 µm; the diameter of the tube heading to the caudal part of the body is 3 µm along the whole body. A small number of large (8.7 µm) nuclei and numerous small (2–3 µm) stichocytes are observed in the stichosoma. Trophosoma starts behind the nerve ring, 1.5 mm from the cephalic part, ending 101 µm from the terminal end of the tail. Vulva is pushed back from the middle part of the body. Cross-section of vulva is slightly inclined from the body axis. Length of vulval transverse section is 15 µm and width is 1.5 µm. Around the cross-section of the vulva (view from above) is a clearly defined wide, oval, cuticular ring ( Figures 1c View Figure 1 and 2e View Figure 2 ). Length of vulval ring is 36–37 µm, width 23–25 µm. Vulval labia are not prominent from the body surface, and they are not visible. The channel of the vulval cross-section in the vagina is first perpendicular to the body axis, then bent like an arch towards the frontal part of the body; it merges with the vagina in the middle, making a blunt or right angle ( Figures 1c View Figure 1 and 2e View Figure 2 ). Vagina is pear-shaped and elongated. Anterior part of vagina is visibly thickened. Middle and terminal parts are cylindrical and arcuate; anterior part of vagina is slightly longer than the posterior part. Anterior part of the ovary ends at the frontal part of trophosome; the posterior part does not reach the terminal part of the trophosome. Oocytes in the ovary are arranged in 3–4 rows. The merged holes, exiting out from the gland, are clearly visible in the cuticle of the terminal part of the tail ( Figures 1e, 1f View Figure 1 , and 2c View Figure 2 ).

Etymology. The new species was named according to the place of its discovery: Devi Cave.

Biology. Its host is unknown.

3.3. Diagnosis and relationships

Adult females of the newly described species M. devii sp. nov. are similar to the females of M. melusinae Rubzov , described in the genus Mesomermis ( Rubzov, 1966) . The structure of stoma is identical for these two species.

The differences between females of Mesomermis devii sp. nov. and its morphologically closely related species M. melusinae are provided in the Table.