Metaporcelaimus declivicaudatus, 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 : 136-139

Metaporcelaimus declivicaudatus sp. n.

( Figs 4 & 5 )

Material examined: Eight females and seven males from a single location; in good state of preservation.

Measurements: See Table 1.

Description. Adult: Slender (a = 30–38) nematodes of medium to large size, 2.8–3.7 mm long. Body cylindrical, slightly tapering towards both extremities, but more so towards the posterior end as the tail is conical. Habitus curved ventrad after fixation, especially in posterior body region, C-shaped. Cuticle two-layered, 2.5–3.5 µm thick at anterior region, 5–6 µm at midbody and 8–10 µm on tail; outer layer thin and with constant thickness throughout body and bearing fine transverse striation; inner layer visibly thicker than the outer one. Cervical lacunae absent. Lateral chord 21–28 µm wide, occupying 24–29% of mid-body diameter, with gland bodies perceptible in some specimens. Two ventral and one or two dorsal pores are distinct at level of odontophore. Lip region sharply offset by deep constriction, 3–3.5 times as broad as high and one-fourth to one-third (25–31%) of body diameter at neck base; lips moderately separate from each other, rounded; labial and cephalic papillae hardly protruding. Amphid fovea funnel-shaped, its aperture 10–11.5 µm or less than one-half (38–47%) of lip region diameter. Cheilostom nearly cylindrical, lacking any differentiation. Odontostyle robust, 3.7–4.4 times as long as wide, nearly as long (1.0–1.1 times) as lip region diameter, and 0.7–0.9% of body length; its aperture 16.5–19.5 µm long, occupying up to three-fourths (69–75%) its length. Guiding ring plicate. Odontophore linear, rod-like, 1.6– 2.1 times the odontostyle length. Pharynx consisting of a muscular anterior region enlarging very gradually, basal expansion 318–406 µm long, occupying 48–56% of total neck length; gland nuclei located as follows (n = 5): DO = 50–51%, DN = 53–56%, S1N1 = 63–67%, S1N2 = 73–77%, S2N = 85–89%. Nerve ring at 192–231 µm or 28–33% of total neck length from the anterior end. Cardia conoid, 22–40 × 20–31 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.

Female: Genital system didelphic-amphidelphic, with both branches equally developed, anterior 356–480 µm or 11–14% of body length, and posterior 442–505 µm or 14–15% of body length. Ovaries reaching the uterusoviduct junction, anterior 213–227 µm, posterior 202–211 µm long; oocytes arranged first in two or more rows, then in a single row. Oviduct consisting of slender part made of prismatic cells and moderately developed pars dilatata with visible lumen. A marked narrowing, surrounded by a muscular sphincter, separates oviduct and uterus. Uterus 276–320 µm long or 3.0–3.4 times the corresponding body diameter, and tripartite, that is consisting of a spheroidal distal portion close to sphincter, a more slender intermediate section with narrow lumen, and a thicker proximal portion with wide lumen inside. Abundant sperm cells present in both distal and proximal uterine regions. Vagina extending inwards 52–63 µm, occupying one-half to two-thirds (54–65%) of body diameter: pars proximalis 38–47 × 19–28 µm, with somewhat sigmoid walls and surrounded by weak musculature, pars refringens with two adjacent trapezoidal pieces measuring 10.5–14 × 10–13.5 µm, and a combined width of 23–28 µm, pars distalis 4–5 µm long. Two cells, one anterior and other posterior, present at both sides of vagina. Vulva a slightly post-equatorial, transverse slit. Prerectum 2.4–3.1, rectum 0.8–0.9 times the anal body diameter long. Tail conical with rounded tip, ventrally straight, dorsally regularly convex; inner core very slightly notched at the end of its dorsal side; hyaline portion 9.5–17.5 µm; inner cuticle layer showing a terminal discontinuity at tail end; caudal pores two pairs, both sub-dorsal, in posterior half of tail.

Male: Genital system diorchic, with opposed testes. Sperm cells 3.5–4 × 6.5–9 µm, oval in shape. In addition to the ad-cloacal pair, there is a series of 12–14, somewhat irregularly spaced, ventromedian supplements, 10–21 µm apart, two or three of them lying within the range of spicules, the posteriormost situated 48–57 µm from the cloacal aperture. Spicules dorylaimid, their total length along the arc 1.2–1.3 times that at the chord, 6.3–7.5 times longer than wide and 2.0–2.3 times longer than body diameter at the cloacal aperture: dorsal side regularly convex and ventral contour strongly concave with slightly or not expressed hump and almost median hollow; curvature 106–116°; head 15–24 µm, occupying 14–21% of spicule total length, its dorsal side strongly curved at anterior end and 1.5–1.8 times longer than the ventral one, which is almost straight; median pieces 14–18 times as long as wide, occupying 29–41% of spicule maximum width, reaching the tip of the spicule; posterior end of spicules 6–7.5 µm broad. Lateral guiding pieces with straight edges, 20–24 µm long, deeply bifurcate distally. Tail similar in shape to that of female, but appreciably more curved ventrad.

Diagnosis. The new species is characterized by its 2.88–3.66 mm long body, lip region offset by deep constriction and 23–28 µm broad, odontostyle 24–26 µm long with aperture occupying 69–75% of its length, neck 634–788 µm long, pharyngeal expansion 318–406 µm long or 48–56% of total neck length, uterus tripartite and 276–320 µm long or 3.0–3.4 times the corresponding body diameter, pars refringens vaginae with two adjacent trapezoidal sclerotized pieces, vulva transverse (V = 51–55), tail conical (45–65 µm, c = 53–63, c’ = 1.0–1.2) with rounded terminus and appreciably more curved ventrad in males, spicules 102–113 µm long, and 12–14 spaced ventromedian supplements without hiatus.

Relationships. In having comparatively large size (body length> 2.5 mm) and odontostyle (length> 20 µm), distinct pars refringens vaginae, and tail with rounded terminus, M. declivicaudatus sp. n. resembles M. digitalis , M. parmus ( Thorne, 1974) Álvarez-Ortega & Peña-Santiago, 2013 and M. placus ( Thorne, 1974) Álvarez-Ortega & Peña-Santiago, 2013 . It differs from M. digitalis in its comparatively shorter female tail (c = 53–61 vs c = 47–53) with regular (vs notched) posterior part of its inner core and without (vs with) a perceptible posterior dorsal concavity, and males as frequent as females (vs male absent). From M. parmus and M. placus , both only known to occur in the USA, in its less slender body (a = 30–38 vs a> 40), broader lip region (23–27 vs 16–18 µm), longer odontostyle (24–26 vs up to 22 µm), and longer neck (634–788 vs less than 560 µm). Besides, it can be easily distinguishable from M. parmus by its much longer spicules (102–113 vs 50 µm) and higher number (12–14 vs 6) of ventromedian supplements without (vs with) hiatus, and from M. placus in its larger general size (body length 2.80–3.71 vs 2.58–2.78 mm).

The new species also resembles M. romanicus , but it differs in its broader lip region (23–27 vs 16–18 µm), longer (24–26 vs 17–19 µm) and more robust odontostyle, longer spicules (102–113 vs 84–93 µm), and tail without (vs with) an appreciable dorsal concavity at the end of its dorsal side.

Type locality and habitat. Ukraine, Lviv region, Krupske village (N 49°27'13.01", E 24°02'20.18"), in a meadow on the bank of Dnister river .

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

Etymology. The specific name is a compound Latin term referring to tail morphology that characterizes the new species.

Figures

FIGURE 4. Metaporcelaimus declivicaudatus sp. n. A, B: Anterior region in lateral, median view. C: Lip region in lateral, surface view. D: Pharyngo-intestinal junction. E: Male, posterior body region. F: Female, caudal region. G: Spicule. H: Vagina. I: Female, anterior genital branch.

FIGURE 5. Metaporcelaimus declivicaudatus 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: Female, caudal region. G: Male, posterior body region. H, I: Male, caudal region. (Scale bars = 10 µm.)