Rhabdias aegyptiaca El-Garhy & Garo 2006

Rhabdias aegyptiaca El-Garhy & Garo, 2006 (Figs. 1–4) (Syn. Rhabdias africanus of Abdel-Hakeem et al. [2022] nec Kuzmin, 2001) Host: Sclerophrys regularis (Reuss); Anura: Bufonidae; Common African toad. Locality: From Abu-Rawash, Kerdasa, north of Giza, Egypt, 30°01’33”N, 31°04’18”E. Site of infection: Lung cavity and inside the lung alveoli. Prevalence: 30 of 40 Sclerophrys regularis (75.0% infected). Intensity: 1–40 worms/host specimen. Mean intensity: 11.7 (350/30) worms. Relative density/abundance: 8.8 (350/40) worms. Deposited specimens: Collector HT, Neotype (AU) 2023.20.Rr01; Paratypes (n = 8) (AU) 2023.20.Rr02–Rr09; Vouchers (n = 11) (AU) 2023.20.Rr10–Rr20. Representative DNA sequences: cox 1 mtDNA (GenBank accession no. MZ820693); ITS2 rDNA (GenBank accession no. MZ853954); 28S rDNA (GenBank accession no. MZ820429); 28S-ITS rDNA (GenBank accession no. OL998834). Amended description. [Based on 20 gravid specimens. Comparative critical measurements, morphometric percentages, and morphometric ratios are given in Tables 3 & 4.] Medium-sized, slender nematode with almost parallel margins, range 4,400 –7,700 µm (mean 5,900 ± 200; 16.9%) long. Body cuticle inflated, with transverse striations/folds (Figs. 1A, 3D). Inflation widening from anterior end to post esophagi-intestinal junction by short distance, keeping the same widening towards beginning of last third of the body, then narrowing towards in caudal region; pronounced caudal inflation around anus and rapidly narrowing towards posterior end leaving naked tail tip (Figs. 1F, 1G, 2D, 2E, 3F, 3G). Lateral cuticular-lined pores, small, extending in longitudinal row on each lateral side of body post beginning of esophageal level by short distance till forward slightly from tail tip (Figs. 1B, 2A), regularly distributed at distances of 35–39 µm and surrounded by thickened portion of cuticular inflation (Fig. 3E). Pores connected to hypoderm by short tubular narrow ducts piercing inflated layer of cuticle (Fig. 1B). Anterior end narrow, truncated in lateral view, round in apical view; abruptly widening posteriorwards from level of esophageal apex followed by gradual widening up to first 1/5–1/4 of body length (Figs. 1A–1C, 2A, 2B), keeping the same widening towards beginning of last 1/9–1/8 of the body, then gradually narrowing towards posterior extremity and with more abruptly tapering in caudal region (Figs. 1F, 1G, 2D, 2E, 3F, 3G). Body width at esophago-intestinal junction 82–150 µm (114 ± 5.2; 20.5%) breadth, 1.2%–3.0% (2.0% ± 0.1; 24.1%) of body length; maximum width at vulva region, 147–375 µm (261 ± 14.9; 25.6%) breadth, 2.9%–7.2% (4.4% ± 0.2; 23.5%) of body length; at anus level 44–113 µm (81 ± 3.7; 20.8%) breadth, 0.7%–1.9% (1.4% ± 0.1; 20.4%) of body length. Oral opening small, circular, with an internal sclerotized cuticle constituting a serrate ring (Figs. 1D, 1E, 3C). Four submedian lips distinct (two dorso-lateral and two ventro-lateral), situated close to oral opening with inner edges overhanging edge of oral opening; each bearing one prominent large elongated internal labial papilla only (Figs. 1D, 1E, 3A–3C). Two lateral lips (pseudolabia) reduced in a small elevation of body-wall, situated farther from oral opening than submedian ones; each possessing one semi-internal small elongated labial papilla located just near their apex (Figs. 1D, 1E, 3A–3C). Amphids positioning on more posterior surface of outer edge of each pseudolabium. Velum not evident. Vestibulum almost barrel-shaped, 8–14 µm (11 ± 0.5; 20.3%) long, lined with thin cuticle. In apical view, entrance of buccal capsule oval to semi-circular (Figs. 1D, 1E, 3C). Buccal capsule, small, cup-shaped with thick sclerotized uniform walls (Figs. 1B, 1C, 2A, 2B), 7–16 µm (13 ± 0.5; 14.5%) depth and maximum width at midlength of its depth level 11–17 µm (15 ± 0.4; 10.7%). Buccal capsule length to width ratio 0.52–0.97 (0.85 ± 0.03; 14.11%). Posterior part of buccal capsule contacting anterior end of esophagus (Figs. 1B, 1C, 2A, 2B). Esophagus, comparatively narrow, short, club-shaped, with a slightly rounded anterior end and a more rounded posterior one (Fig. 1A), 336–428 µm (377 ± 5.4; 6.5%) long, occupying 4.9%–8.4% (6.5% ± 0.2; 14.3) of total body length. Apex of esophagus encircling almost posterior half of the buccal capsule forming a shoulder-like structure (Figs. 1B, 1C, 2A, 2B). Slight dilatation present just at the first third of esophagus length or directly anterior to it (Figs. 1A, 1B and 2A); posterior bulbar part oval (Fig. 1A). Esophagus width 17–32 µm (25 ± 1; 17.9%) at anterior end, 30–45 µm (34 ± 0.9; 13.0%) at level of nerve ring and 36–58 µm (44 ± 1.3; 12.9%) at middle of muscular part; bulbar part 42–67 µm (55 ± 1.6; 12.8%) wide. Nerve ring small, encircling muscular portion of esophagus just posterior to its dilatation (Fig. 1A), at 103–131 µm (117 ± 2; 7.6%) from anterior end of esophagus, representing 26.8%–35.5% (31.1% ± 0.6; 8.9%) of esophagus length; and at 110–147 µm (130 ± 2.5; 8.6%) from anterior end of body, 0.2%–2.8% (1.9% ± 0.1; 27.3%) of body length. Two lateral cords originating from hypodermal cells, running longitudinally along ventral and dorsal midline of the body (Figs. 4A–4C). Excretory pore located posterior to nerve-ring, somewhat conspicuous, at 170–207 µm (190 ± 2; 4.7%) from anterior end of body or 2.6%–3.9% (3.2% ± 0.2; 28.0%) of body length. Excretory duct thin, tubular, poorly visible in most specimens, straight in both cuticular and hypodermal parts. Excretory glands inconspicuous in gravid individuals; in an early mature individual, excretory glands two, faint, elongated, subequal in size, shorter than esophagus, slightly widening towards the posterior end forming a drop-like rear part, and terminating at the base of esophageal level. Intestine simple, wide, occupying whole internal body space anterior to level of anterior bend of reproductive system and posterior to its posterior bend; anterior part of intestine wider than esophageal bulb (Fig. 1A), then widening posteriorly reaching maximum width in posterior part of body anterior to anal opening. Wall of intestine composed of a single layer of cylindrical and voluminous cells with spherical nuclei and grainy cytoplasm of an apparent basophilic nature (i.e., dense blue-colored cytoplasm) constituting allmost parts of intestine (Fig. 4A) except for posteriormost part near rectal region that having an acidophilic nature (i.e., red-colored cytoplasm) (Fig. 4B); numerous microvilli constituting intestinal epithelium (Figs. 4A, 4B). Pre-intestinal distance 351–438 µm (390 ± 5.3; 6.1%) long, 5.1%–8.7% (6.7% ± 0.2; 14.5%) of body length. Rectum short, slightly curved ventrally, with thick sclerotized walls and narrow lumen (Figs. 1F, 1G, 2D, 2E). Posterior portion of intestine separated from rectum by a pre-rectal muscular sphincter (Fig. 1F, 1G). Anus pore-like to a transverse slit with a conspicuous post-anal ventral elevation of body wall (Figs. 1F, 1G, 2D, 2E, 3F, 3G). Pre-anal distance 4,060 –7,410 µm (5,710 ± 220; 17.5%) long, 93.2%–97.6% (96.1% ± 230; 1.1%) of body length. Salient large cuticular inflation anterior and posterior to anus in most specimens (Figs. 1F, 1G, 2D, 2E). Reproductive system amphidelphic, typical of Rhabdias with approximately similar anterior and posterior limbs in length and shape. Both limbs of reproductive system reflected, bending in the region of oviduct (seminal receptacle) parts (Fig. 4C). Oogonia located on dorsal side, along intestine, and arranged in almost straight columns (Fig. 4D). Mature ovulae arising from division of oogonia, arranged on a loop surrounded by layers of discus progligerus (Figs. 4C, 4E). Male gametes lining the lumen of the oviduct as numerous small globular to semi-polygonal cells with evident nuclei (Fig. 4F). Vulva somewhat post-equatorial, at 2,500 –3,500 µm (2,900 ± 90; 10.7%) from anterior end or 50.2%–58.6% (54.3% ± 0.9; 5.7%) of body length. Vulva rounded opening with salient lips (Figs. 1H, 1I, 2C). A salient large prominent cuticular inflation present at cephalic and caudal sides of the vulval opening in all specimens (Figs. 1H, 1I, 2C). Vagina short, transverse, straight, lined with thin cuticle (Figs. 1H, 1I, and 2C). Uteri amphidelphic, tubular, wide, thin-walled, filled with numerous eggs arranged in 3–4 longitudinal rows (Fig. 1H, 4G); most eggs containing fully developed larvae -particularly those close to vulva- (Fig. 1I, 1J, 2G, 3H, 4G), and some at morula stage (Fig. 2F). Larvated eggs oval, 99–107 µm (104 ± 0.9; 3.1%) × 53–73 µm (65 ± 1.9; 9.7%). Tail conical, less elongated, gradually tapering from level of anus to posterior end, wholly covered with inflated cuticle except for end tip (Figs. 1F, 1G, 2D, 2E, 3F, 3G). Tail tip medium-long, tubular, thin, needle-like. Tail length 156–317 µm (223 ± 9.8; 19.7%) long or 2.4%–6.8% (3.9% ± 0.2; 27.1%) of body length. Phasmids situated at about midlength of tail. Variability in adult specimens. Applying the coefficient of variation on the most significant morphometrical features in adult specimens clarified a wide range of variability, ranging from comparatively less variable to mild or more variable: Some characteristics exhibited comparatively less variability (CV <10%) that are functional in differentiation and comparisons. These metrical characters included values of esophagus length, distance from anterior end of esophagus to nerve ring, pre-nerve ring distance, distance from anterior end of body to excretory pore, pre-intestinal distance, and eggs size; in addition to ratio of pre-anal distance in relation to body length, pre-vulva distance in relation to body length and distance from anterior end of esophagus to nerve ring in relation to esophagus length. A mild range of variability (10%≤ CV ≤15%) has been observed in buccal capsule width, buccal capsule length to width ratio, esophageal bulb width, esophagus length as ratio of body length, and esophagus width at t