Metaporcelaimus concinnus, Krainer & Susulovsky & Peña-Santiago, 2018

Krainer, Liubomyr, Susulovsky, Andrij & Peña-Santiago, Reyes, 2018, The genus Metaporcelaimus Lordello, 1965 (Nematoda, Dorylaimida, Aporcelaimidae) in Ukraine: Description of one known and two new species without hiatus, Zootaxa 4497 (1), pp. 127-140 : 131-136

Metaporcelaimus concinnus sp. n.

( Figs 2 & 3 )

Material examined: Nine females and nine males from three locations in Lviv, in good state of preservation.

Morphometrics: See Table 2.

Description. Adult: Slender to very slender (a = 43–55) nematodes of large size, 3.1–4.6 mm long. Body cylindrical, tapering towards both extremities, but more so towards posterior end as the tail is conical. Habitus curved ventrad after fixation, especially in posterior body region, J-shaped. Cuticle two-layered, 2 µm thick at anterior region, 3.5–5 µm along most of the body and 7–7.5 µm on tail; outer layer thin, with constant thickness throughout the body and bearing fine transverse striation; inner layer thicker than the outer one. Cervical lacunae absent. Lateral chord 15–23 µm broad, occupying 23–29% of mid-body diameter. One or two ventral and one or two dorsal pores are often present at level of odontophore. Lip region offset by deep constriction, angular and sharply broader than the adjacent body, 2.7–3.3 times as broad as high, and up to one-third (22–32%) of body diameter at neck base; lips distinctly separate, with slightly protruding labial and cephalic papillae. Amphid fovea funnel-shaped, its aperture 6.5–8 µm or less than one-half (35–48%) of lip region diameter. Cheilostom nearly cylindrical, lacking any differentiation. Odontostyle typical of the genus, 4.1–4.8 times as long as wide, 0.9–1.1 times as long as lip region diameter, and 0.4–0.6% of body length; its aperture 13.5–14.5 µm long or occupying 74–84% of odontostyle length. Guiding ring plicate. Odontophore linear, rod-like, 1.6–1.9 times the odontostyle length. Anterior region of pharynx enlarging very gradually, basal expansion 470–574 µm, occupying 62–66% of total neck length; gland nuclei located as follows (n = 4): DO = 40–45%, DN = 44–49%, S1N1 = 52–55%, S1N2 = 64–68%, S2N = 83–87%. Nerve ring at 174–201 µm or 22–25% of total neck length from anterior end. Cardia conoid, 16–28 × 16–28 µm. Pharyngo-intestinal junction surrounded by a delicate ring-like structure, which appears visibly asymmetrical as its dorsal side is more developed and forming a lobe. A dorsal cell mass is perceptible in several specimens at level of anterior end of intestine. Tail conical with rounded tip, ventrally nearly straight or slightly convex, dorsally convex and with a weak but noticeable concavity at the end; inner core nearly reaching the tail tip, dorsally visibly notched; hyaline terminal portion 6.5–11 µm long; inner cuticle layer with a gap (discontinuity) at tail terminus; caudal pores two pairs, one subdorsal at the middle of tail, another sublateral in posterior half of tail.

Female: Genital system didelphic-amphidelphic, with both branches equally developed, anterior 481–594 µm or 12–16% of body length, and posterior 491–678 µm or 13–18% of body length. Ovaries almost reaching the uterus-oviduct junction, anterior 111–214 µm, posterior 111–168 µm long; oocytes arranged first in two or more rows, then in a single row. Oviduct consisting of a slender part with prismatic cells and a moderately developed pars dilatata with distinct lumen. A marked narrowing surrounded by a muscular ring (sphincter) separates oviduct and uterus. Uterus 317–458 µm long or 3.9–5.7 times the corresponding body diameter, and tripartite, that is consisting of a spheroidal distal portion close to the sphincter, a more slender intermediate section with narrow lumen, and a thicker proximal portion with wide lumen. Abundant sperm cells present in both distal and proximal uterine regions. Uterine egg ovoid, 124 × 55 µm, 2.3 times longer than wide. Vagina extending inwards 39–46 µm, occupying ca one-half (49–57%) of body diameter: pars proximalis 29–36 × 16–20 µm, with somewhat sigmoid walls and surrounded by weak musculature, pars refringens (lateral view) with two rounded triangular pieces measuring 7.5–10 × 7–9.5 µm, separated by a less refringent intermediate area, and with a combined width of 17– 20 µm, pars distalis 2.5–4 µm long. Vulva a short, nearly equatorial, longitudinal slit. Prerectum 3.7–5.8, rectum 1.3–1.5 times the anal body diameter long.

Male: Genital system diorchic, with opposed testes. Sperm cells 3–3.5 × 7.5–10 µm, oval in shape. In addition to the ad-cloacal pair, there is a series of 10–14, somewhat irregularly spaced, ventromedian supplements, 11–21 µm apart, one or two of them lying within the range of spicules, with the posteriormost situated at 41–53 µm from the cloacal aperture. Spicules dorylaimid, their total length along the arc 1.1–1.2 times that at the chord, 5.1–6.1 times longer than wide and 1.8–2.2 times longer than body diameter at the cloacal aperture: dorsal side regularly convex and ventral side with moderately expressed hump and hollow, the former located at 36–43% of spicule total length from the anterior end; curvature 122–134°; head 11–21 µm, occupying 13–25% of spicule total length, its dorsal side conspicuously curved at its anterior end and 1.4–2.0 times longer than the ventral one, which is nearly straight; median pieces 16–19 times as long as wide, occupying 23–28% of spicule maximum width, reaching the posterior end of the spicule and with visibly furcated tip; posterior end of spicules 7.5–8 µm broad. Lateral guiding pieces with slightly sigmoid edges, 20–26 µm long, distally with shallow depression.

Diagnosis. The new species is characterized by its 3.09–4.58 mm long body, lip region offset by deep constriction and 16.5–19.5 µm broad, visibly wider than the adjacent body, odontostyle 17–19 µm long with aperture occupying 74–84% of its length, neck 745–865 µm long, pharyngeal expansion 470–574 µm long or 62– 66% of total neck length, uterus tripartite and 317–458 µm long or 3.9–5.7 times of corresponding body diameter, pars refringens vaginae with two separate triangular sclerotised pieces, vulva longitudinal (V = 49–53%), tail conical (44–54 µm, c = 67–94, c’ = 1.0– 1.3 in females), spicules 79–86 µm long with strongly bifurcate distal end, and 10–14 irregularly spaced ventromedian supplements without hiatus.

Relationships. The new species is easily recognizable and distinguishable from its congeners—except perhaps M. silvanus ( Vinciguerra & Giannetto, 1983) Álvarez-Ortega & Peña-Santiago, 2013 , see remarks—by its longitudinal (vs transverse) vulva, with pars refringens vaginae consisting of two separate (vs close together) pieces. In having comparatively large size (body more than 2.5 mm long), odontostyle less than 20 µm long, welldeveloped pars refringens vaginae, and tail with rounded terminus, M. concinnus sp. n. is very similar to M. digitalis ( Loos, 1949) Andrássy, 2001 , M. romanicus and M. sublabiatus ( Thorne & Swanger, 1936) Andrássy, 2001 . Nevertheless, it differs from M. digitalis , only known to occur in Sri Lanka, in its more slender body (a = 43– 55 vs a = 33), much shorter odontostyle (16.5–19.5 vs 24 µm), shorter female tail (44–54 vs 62–65 µm, c = 67–94 vs c = 47–53), and male as frequent as female (vs male absent). From M. romanicus , the most similar species, it differs in its relatively more slender body (a = 43–55 vs a = 38–47), comparatively broader lip region (conspicuously broader than vs nearly equal to adjacent body), and structure of spicules (distally strongly bifurcate vs not furcated). From M. sublabiatus , a poorly known species from the USA, but also recorded in Poland and Spain, in its comparatively more slender body (a = 44–54 vs a = 33–43), shorter caudal region (40–54 vs 58–59 µm, c = 67–93 vs c = 52–56, c’ = 1.0–1.3 vs c’ = 1.4–1.6), and irregularly spaced (vs nearly contiguous) ventromedian supplements lacking (vs having) hiatus.

The new species also resembles M. labiatus (de Man, 1880) Andrássy, 2001 , but differs in its broader lip region (17–19 vs 15–16 µm), longer odontostyle (17–19 vs 14–16 µm), neck morphology (regularly tapering vs distinctly narrowing at level of odontophore base), shorter tail (44–54 vs 61–98 µm, c’ = 1.0–1.3 vs c’ = 1.4–1.9), and higher number (10–14 vs 7) of ventromedian supplements without (vs with) hiatus.

Type locality and habitat. Lviv, Ukraine: Lychakiv Park (N 49°50'06.59", E 24°03'54.08"), in soil around roots of grasses.

Other localities and habitats. Two localities and habitats also in Lviv, Ukraine, near the type one: Circus garden square (N 49°50'21.06", E 24°00'47.96"), in soil around roots of Acer platanoides L. (Population 1 in Table 2); and Nischynskogo garden square (N 49°50'26.26", E 24°03'55.96"), in soil around roots of Acer platanoides L. (Population 2 in Table 2).

Type material. Female holotype, one female and three male paratypes deposited in the nematode collection of the State Museum of Natural History, NASU, Lviv, Ukraine. One female and three male paratypes at the Museum and Institute of Zoology, PAS, Warsaw, Poland.

Etymology. The specific epithet is a Latin term meaning ‘neat, elegant or pretty’ and reflects the graceful general appearance of the new species.

Remarks. One male paratype bears a second, non-functional odontostyle embedded within pharyngeal tissue at 98 µm from the anterior end. It is 17 µm long and 3.5 µm wide, and its aperture measures 12.5 µm long.

As mentioned, the most relevant diagnostic feature of M. concinnus sp. n. is its longitudinal vagina, with pars refringens vaginae consisting of two separate sclerotized pieces, indeed a remarkable character in Metaporcelaimus as other representatives of the genus, except M. silvanus from Italy, present a transverse vulva, with contiguous sclerotized pieces in their pars refringens vaginae. Nevertheless, there are very significant differences between the Italian species and M. concinnus sp. n., for instance, a much larger general size in the Ukrainian species (body length 3.5–4.7 vs 1.6–1.8 mm), more slender body (a = 43–52 vs 28–34), more anterior vulva (V = 49–53 vs 54–59%), tail with rounded (vs acute) tip, longer spicules (79–86 vs 30 µm), and hiatus present (vs absent).

Figures

FIGURE 2. Metaporcelaimus concinnus sp. n. A: Anterior region in lateral, median view. B: Lip region in lateral, surface view. C: Pharyngo-intestinal junction. D: Female, posterior genital branch. E: Male, posterior body region. F: Vagina. G: Male, caudal region and spicule. H: Female, caudal region. I: Pars dilatata oviductus-uterus junction.

FIGURE 3. Metaporcelaimus concinnus sp. n. (LM). A: Lip region in lateral, surface view. B: Anterior region in lateral, median view. C: Pharyngo-intestinal junction. D: Vagina. E, F: Vulva in ventral view. G: Pars dilatata oviductus-uterus junction. H: Female, caudal region; I: Male, caudal region and spicule. (Scale bars = 10 µm.)