Desmicola ryukyuensis, Morffe & García & Hasegawa, 2023

Morffe, Jans, García, Nayla & Hasegawa, Koichi, 2023, Morphological and molecular characterization of Desmicola ryukyuensis n. sp. (Nematoda: Oxyuridomorpha: Thelastomatidae) from the wood-feeding cockroach Panesthia angustipennis yayeyamensis Asahina, 1988 (Blattaria: Blaberidae) in the Ryukyu Archipelago, Japan, Zootaxa 5389 (2), pp. 213-226 : 216-224

Desmicola ryukyuensis n. sp.

Fig. 1 A–F , Fig. 2 A–H , Fig. 3 A–H , Fig. 4 A–K

Type material. Holotype: ♂, Japan, Ryukyu Archipelago, Iriomote Island, Okinawa Prefecture, Yaeyama District , Taketomi Town , Aira River ; 24º20’34.2”N, 123º54’44.8”E; in Panesthia angustipennis yayeyamensis ; 24/X/2021; H. Nagaya coll.; CZACC 11.7486 . Paratypes: 5♂♂, same data as the latter; CZACC 11.7487 –11.7491 . 14♀♀, same data as the latter; CZACC 11.7492 –11.7505 .

Measurements. Table 1 .

Description

Male. Body smaller and less robust than that of females; C-shaped in heat-killed specimens. Anterior end truncated. Lateral alae well-developed expanding from ca. level of 7 th –8 th cuticular annuli posterior to head capsule ( Fig. 2A ) to ca. 3–6 annuli before cloaca ( Fig. 2D ). Head capsule conical, with smooth cuticle ( Fig. 2A, B ). Cuticle unarmed, with conspicuous, dilated, wide annuli from base of head capsule to ca. level of cloaca ( Fig. 2A, D ). Annuli ca. 9 µm wide next to the head capsule and ca. 6 µm wide close to cloaca. A series of 7–9 (mostly 8) modified, ventrally projected annuli present in posterior third of body ( Fig. 2E ). Ventral projections of modified annuli triangular, the cuticle of their anterior surface presenting a central groove that originates on the tips of the projections ( Fig. 2F ). Several paired depressions located at both sides of central groove of each ventral projection ( Fig. 2F ). Number of depressions ranging from one pair in shortest projection to four pairs in largest ones ( Fig. 2F ). Mouth hexagonal, with three small triangular lips ( Fig. 2C ). Four pairs of fused, elongated (ca. 5 µm in length) sub-median papillae surround the mouth ( Fig. 2C ). Amphids slit-like (ca. 2 µm in length), lateral in position ( Fig. 2C ). Buccal capsule short, with thickened walls. Oesophagus consisting of muscular, sub-cylindrical corpus, slightly expanded at anterior end and decreasing in diameter towards cylindrical isthmus. Basal bulb rounded, valve-plate well-developed. Cardia small. Intestine simple, sub-rectilinear, its anterior region dilated. Nerve ring encircling corpus at its posterior half, ca. 87% of its length. Excretory pore ventral, located at level of isthmus. Monorchic. Testis ventral, reflexed at ca. one body-width posterior to basal bulb, distal flexure ca. a body-width long. Vas deferens divided into three regions: anterior region filled with rod-like spermatids, median region with large, rounded cells and posterior region with smaller cells, gradually tapering towards its junction with cloaca. Posterior lip of cloaca enlarged, protruded, posteriorly directed. Spicule with distinct, rounded capitulum; shaft straight, thickened at level of first quarter of its length and tapered towards the pointed, ventrally curved tip. Eight copulatory papillae present, two pre-cloacal, two adcloacal and four post-cloacal. Pre-cloacal pair ventromedian, located just anterior to the cloaca, papillae close to each other on top of a conical prominence ( Fig. 2G, H ). Adcloacal pair of papillae formed by large, conical and prominent papillae, flanking cloaca at lateral sides ( Fig. 2G, H ). Sensillum of each adcloacal papilla surrounded by ca. 12 small protuberances. First post-cloacal pair consisting of small papillae, situated closely to each other on tip of protruded posterior lip of cloaca ( Fig. 2G, H ). Second post-cloacal pair consisting of minute papillae, sub-dorsal, located ca. at midpoint of caudal filament (ca. 40 µm posterior to cloaca) ( Fig. 2D ). Tail with the anterior portion conical (ca. one fifth of the tail length), continuing with filament ending in a sharp tip ( Fig. 2D ). Phasmids slit-like, lateral in position, at beginning of caudal filament (ca. 16 µm posterior to cloaca) ( Fig. 2H ).

Female. Body comparatively robust, spindle-shaped, widening gradually from base of semispherical head capsule, body width uniform from base of oesophagus to near level of the vulva, then diminishing towards anus. Cervical cuticle unarmed ( Fig. 4A ). Cuticle thick, markedly annulated by retrorse annuli from base of head capsule to just before level of anus ( Fig. 4A, B ). Annuli from base of head capsule to beginning of lateral alae ca. 2–5 µm wide and set-off each other by deep grooves ( Fig. 4A ). Annuli of the rest of body wider: ca. 8 µm wide at level of first portion of lateral alae, ca. 12 µm wide at level of vulva and ca. 8 µm wide near level of anus. Lateral alae well-developed from base of corpus (ca. 23 annuli posterior to base of head capsule) terminating at anus level ( Fig. 4A, B ). Oral opening triangular. Three large, isometric lips surrounding mouth, arranged as one dorsal and two sub-ventral lips, coinciding with sides of oral aperture ( Fig. 4F ). Lips triangular, partially fused at their bases ( Fig. 4F ). Distal tip of each lip bifurcated by a shallow cleavage ( Fig. 4G ). Complex ornamentations present in lips, consisting of cuticular ridges (ca. 1 µm wide) with rounded tips ( Fig. 4F ). Ornamentations of dorsal lip consist of two symmetrical sets, each one with two asymmetrical horseshoe-like and one comma-shaped ridges ( Fig. 4I ). Asymmetrical horseshoe-shaped ridges of each set arranged as one with convex side pointing to oral opening and other located dorsally to the first one, next to comma-like ridge with their concave sides facing each other ( Fig. 4I ). Sub-ventral lips presenting an hourglass-like ornamentation displaced to the ventral side of lips ( Fig. 4H ). One base of hourglass-like ornamentation (formed by one sigmoid ridge with a horseshoe-shaped ridge dorsal to it) pointing to center of oral opening, the other (formed by one straight ridge flanked by two colon-like ridges) points to basal side of lips ( Fig. 4H ). A sigmoid ridge located in each interlabial space between sub-ventral lips and dorsal one. Surface of ornamentations covered in tiny, clustered, round protrusions ( Fig. 4J ). Amphids located at sub-ventral lips, lateral in position, horseshoe-like, their convex side directed to the external margin of the head capsule ( Fig. 4H ). Small sensilla present in each interlabial space ( Fig. 4J ). Each sensillum presenting a dorsomedian ridge and a distal bifurcation forming two teeth ( Fig. 4J ). Three large, triangular fang-like structures located in each interlabial space, beneath the sensilla ( Fig. 4F ). Fang-like structures with two asymmetrical tips at their distal ends ( Fig. 4J ). Three isomorphic, isometric triangular plates located beneath lips, slightly protrude towards mouth center. Margin of each plate bearing 14 teeth with rounded tips ( Fig. 4G ). Tooth length ca. 1 µm at both sides of plate, increasing in length to ca. 2 µm towards center of plate. Buccal capsule pyriform, wide, notably cuticularized. Oesophagus consists of cylindrical, muscular corpus well set-off from isthmus. Isthmus slightly diminishing in diameter towards junction with rounded basal bulb. Valve-plate of basal bulb well-developed. Cardia well-developed, projecting into intestinal lumen. Intestine simple, sub-rectilinear, its anterior region dilated. Rectum short. Anus a crescent-like slit, its convex side anteriorly directed ( Fig. 4B ). Posterior lip of anus depressed ( Fig. 4B ). Two V-like cuticular ridges located anterior to the anus, at level of endpoints of the anal slit, their vertices anteriorly directed ( Fig. 4B ). Nerve ring encircling procorpus at its posterior half, ca. 65% of its length. Excretory pore ventral, slit-like, ca. 18 µm in length, located at level of isthmus, in a discontinuity of a cuticular annulus ( Fig. 4K ). Vulva a ventromedian transverse slit, ca. 45 µm in length, located ca. midpoint of body (relative to total length of body). Lips of vulva prominent, posterior one hypertrophied, forming a cuticular flap, partially covering the contiguous annulus ( Fig. 4C ). Vagina vera muscular, anteriorly directed. Genital tract didelphic-amphidelphic. Both ovaries reflexed. Oocytes in single rows. Rounded seminal receptacle located between the basal end of anterior ovary and posterior uterus. Eggs broadly oval, with thin and smooth shell. Tail comparatively long, ca. half of body length, subulate with filiform terminal part. Phasmids pore-like, lateral in position, located ca. 30 µm posterior to anus ( Fig. 4B ).

Differential diagnosis

The males of D. ryukyuensis n. sp. resemble those of D. lamdongensis by having modified ventrally projected cuticular annuli in the posterior third of body, similar body length (0.86–1.10 mm vs. 0.99–1.29 mm) and comparative length of the oesophagus (b = 3.6–4.4 vs. 3.1–4.2) and tail (c = 8.1–10.0 vs. 6.4–9.9). They differ by the length of the spicule which is shorter in D. ryukyuensis n. sp. (41–44 µm vs. 48–55 µm). The lateral alae of D. ryukyuensis n. sp. begins at the level of the 7 th –8 th annuli posterior to the cephalic capsule, rather than at the 4 th as in D. lamdongensis .

The spicule of D. ryukyuensis n. sp. is shorter than D. nhatrangenis and D. kinabaluensis (41–44 µm vs. 45–51 µm vs. 62–65 µm) and its distal end is pointed vs. bifurcated in the other two species. Both D. nhatrangensis and D. kinabaluensis males possess a mamelon in the last third of the body ( Hugot et al. 1991) consisting of ventrally dilated annuli with a transversal groove in the middle. The latter feature differentiates them from the males of D. ryukyuensis n. sp., with their modified ventrally projected cuticular annuli triangular in form. The tail of D. ryukyuensis n. sp. is comparatively shorter than in D. nhatrangensis (c = 8.1–10.0 vs. 2.7–4.4). Moreover, the males of D. kinabaluensis differs from the new species proposed herein by its longer (1.38–1.57 mm vs. 0.86–1.1 mm) and less robust (a = 15.7–16.8 vs. 8.9–12.3) body, the shorter oesophagus (b = 4.5–5.2 vs. 3.6–4.4) and the longer tail (c = 4.0–4.6 vs. 8.1–10.0).

The tail of the males of D. ryukyuensis n. sp. is comparatively shorter than that of D. danieli and D. moramangi (c = 8.1–10.0 vs. 6.8–6.9 vs. 4.0–5.4). Also, the spicule of D. ryukyuensis n. sp. is longer than in D. danieli (41–44 µm vs. 38–41).

The females of D. ryukyuensis n. sp. are similar to D. ornata by body length (1.73–1.97 mm vs. 1.77–2.09 mm), the robustness of the body (a = 8.6–12.0 vs. 9.8–17.1), the comparative lengths of the oesophagus (b = 5.8–6.4 vs. 5.7–7.4) and tail (c = 2.4–2.7 vs. 2.3–3.9) as well as the position of the vulva (V% = 48.4–53.3 vs. 48.0–68.0). Both species feature triangular lips partially fused at their bases with their distal tips bifurcated. The ornamentations of the lips are similar in D. ryukyuensis n. sp. and D. ornata . They present the fang-like double-tipped structure in the interlabial spaces and three triangular plates beneath the lips with teeth at their margins. Desmicola ryukyuensis n. sp. differs from D. ornata by the shape of the small sensilla in the interlabial space, with the distal tip bifurcate vs. not bifurcate. Lateral alae are absent in D. ornata and in D. ryukyuensis n. sp. they are present, from to the base of the corpus to the level of the anus.

The females of D. ryukyuensis n. sp. are also similar to D. lamdongensis in body length (1.73–1.97 mm vs. 1.78–2.36 mm) and comparative lengths of the oesophagus (b = 5.8–6.4 vs. 5.1–6.6) and tail (c = 2.4–2.7 vs. 2.1–2.6). They feature horseshoe-like amphids and bifurcate sensilla at the interlabial space. Both taxa can be differentiated by the presence of fused lips in D. lamdongensis vs. partially fused lips in the new species. Desmicola lamdongensis lacks the double-tipped fang-like structures at the interlabial spaces and the toothed plates. The eggs of D. ryukyuensis n. sp. are smaller than D. lamdongensis (58–81×40–55 vs. 88–98×53–65).

The body of D. ryukyuensis n. sp. is shorter than the rest of the species of the genus, namely D. danieli , D. kinabaluensis , D. leidyi , D. moramangi , D. nhatrangensis and D. skrjabini (1.73–1.97 mm vs. 2.23–2.69 mm vs. 3.30–4.23 mm vs. 3.46 mm vs. 2.11–2.52 mm vs. 2.18–2.43 mm vs. 2.98–3.44 mm). However, despite its smaller body length the oesophagus of D. ryukyuensis n. sp. is comparatively longer than some of the aforementioned species: D. kinabaluensis , D. leidyi , D. moramangi , D. nhatrangensis and D. skrjabini (b = 5.8–6.4 vs. 8.4–9.8 vs. 6.9 vs. 6.7–7.5 vs. 7.5–8.4 vs. 7.8). The body of D. ryukyuensis n. sp. is more robust than D. kinabaluensis , D. moramangi , D. nhatrangensis and D. skrjabini (a = 8.6–12.0 vs. 20.2–26.5 vs. 12.5–17.0 vs. 14.5–16.2 vs. 12.6), but comparatively slender than D. leidyi (a = 8.6–12.0 vs. 8.0). The index V´ of D. danieli is larger than D. ryukyuensis n. sp. (V´ = 90.0 vs. 82.2–86.9).

Type locality. Aira River , Taketomi Town , Yaeyama District , Iriomote Island, Okinawa Prefecture, Ryukyu Archipelago, Japan .

Type host. Panesthia angustipennis yayeyamensis Asahina, 1988 ( Insecta: Blattaria: Blaberidae ).

Site . Hind gut.

Etymology. Specific epithet referred to the Ryukyu Archipelago, to which Iriomote Island belongs.

Molecular identification of the host

The BLAST alignment resulted in a high percent identity (99.71%) of the COII sequence of the host with the sequence AB007541 of P. a. yayeyamensis also from Iriomote Island.

DNA studies

Two partial sequences of the D2-D3 region of the 28S rDNA were obtained from a female and a male of D. ryukyuensis n. sp. (743 bp and 742 bp, respectively). Both sequences were identical, in an alignment of 739 bp. The new species differs in 28 homologous positions (in an alignment of 634 bp) from a sequence of an unidentified Desmicola (GQ368463) from a Vietnamese Panesthia ( Spiridonov & Guzeeva 2009) , the only sequence of the genus available in GenBank that comprises the D2-D3 domains of the 28S rDNA.

The new species differs in four homologous positions from a sequence (AM232760) of the D3 domain of the 28S rDNA from D. ornata , parasite of the Australian Panesthia cribata ( Jex et al. 2006) . On the other hand, Desmicola sp. from Vietnam (GQ368463) differs in two homologous positions from D. ornata . These results were obtained in an alignment of 242 bp.

In addition, two partial sequences of the 18S rDNA were obtained from the female and male of the present species (1683 bp and 1680 bp, respectively). Both sequences were identical, in an alignment of 1680 bp.

In both ML and BI phylograms both sequences of D. ryukyuensis n. sp. form a monophyletic clade with strong nodal support, with Desmicola sp. The genus Desmicola form a clade containing Aorurus agile (Leidy, 1849) , Cordonicola sp. , Stauratostoma shelleyi Phillips & Bernard, 2018 , several species of Thelastoma Leidy, 1849 and unidentified thelastomatids. This clade is supported by maximum value of posterior probability for the BI analysis, but has low bootstrap value in the ML analysis.

Figures

FIGURE 1. Desmicola ryukyuensis n. sp. Male. A. Oesophageal region, lateral view. B. Cephalic end, optical section. C. Cephalic end (reconstructed from SEM images). D. Tail, lateral view. E. Spicule. F. Habitus, lateral view.

FIGURE 2. Desmicola ryukyuensis n. sp., SEM images. Male. A. Cephalic end and beginning of the lateral ala, lateral view. B. Cephalic end. C. Cephalic end, en face view. D. Tail, lateral view. E. Modified ventrally projected cuticular annuli, ventro-lateral view (anterior end to the top). F. Detail of the modified ventrally projected cuticular annuli, ventral view (anterior end to the top). G. Cloacal region, lateral view. H. Cloacal region, ventral view. Scale bars: A, D. 20 µm. B, E. 10 µm. C. 2 µm. F, G, H. 5 µm.

FIGURE 3. Desmicola ryukyuensis n. sp. Female. A. Oesophageal region, lateral view. B. Cephalic end, optical section. C. Cephalic end (reconstructed from SEM images). D. Tail, lateral view. E. Vagina. F. Genital tract, lateral view. G. Egg. F. Habitus, lateral view.

FIGURE 4. Desmicola ryukyuensis n. sp., SEM images. Female.A. Cervical region, lateral view. B. Anus region and phasmid, ventro-lateral view. C. Vulva, lateral view. D, E. Cephalic end, ventro-lateral view. F. Cephalic end, en face view. G. Oral opening, en face view. H. Sub-ventral lip. I. Dorsal lip. J. Sensilla and fang-like structure at interlabial space. K. Excretory pore, ventral view. Scale bars: A. 50 µm. B, C, D, E. 10 µm. F, I, K. 5 µm. G, H. 2 µm. J. 1 µm.