Lepidonema, Cobb, 1898

Morffe, Jans, García, Nayla, Breugelmans, Karin, Hasegawa, Koichi & Davis, Andrew K., 2019, Morphological and molecular characterization of Lepidonema magnum Morffe & García, 2010 (Nematoda: Oxyuridomorpha: Hystrignathidae) from Passalus interstitialis Eschscholtz, 1829 (Coleoptera: Passalidae) from Cuba and new locality records for the species, Zootaxa 4551 (2), pp. 221-230 : 223-227

Lepidonema magnum Morffe & García, 2010

Fig. 1 A–H, Fig. 2 A–D

Lepidonema magnum Morffe & García, 2010: 6 –9, fig. 3 A–I, fig. 4 A–G

Material examined. Vouchers: 6♀♀, Cuba, Pinar del Río province, Viñales, Sendero “Maravillas de Viñales”; in

Passalus interstitialis ; IV/2018; M. Iturriaga, C. Hernández coll.; CZACC 11.7115 – 11.7120 . 2♀♀ , same data as the latter; MNHNSD 05.0020 – 05.0021 .

Vouchers: 3♀♀, Cuba, Artemisa province, Sierra del Rosario, El Taburete; in Passalus interstitialis ; 8/IV/ 2012; E. Pardo coll.; CZACC 11.7121–11.7123.

Vouchers: 4♀♀, Cuba, Isla de la Juventud, Sierra de Casas; in Passalus interstitialis ; IV/2014; J. Morffe, N. García, M. Olcha coll.; CZACC 11.7124–7127.

Vouchers: 3♀♀, Cuba, Sancti Spíritus province, Trinidad, Topes de Collantes, Hotel “Los Helechos”; in Passalus interstitialis ; V/2013; E. Fonseca coll.; CZACC 11.7128–11.7130.

Vouchers: 4♀♀, Cuba, Camagüey province, Sierra de Cubitas, Reserva Ecológica “Limones-Tuabaquey”; in Passalus interstitialis ; XII/2015; J. Morffe, N. García coll.; CZACC 11.7131–7134.

Redescription. Female. Body comparatively robust, widening gradually posterior to head, reaching its maximum width at level of the vulva, then narrowing gradually towards tail. Sub-cuticular striae present. Cephalic end bluntly rounded. Cervical cuticle armed with ca. 67 opposite rows of spines, from the base of the first cephalic annule to the midpoint of the basal bulb in some specimens or a short distance further down its base in other specimens. First row of spines with 16 scale-like elements, their distal ends rounded, ca. 5 µm in length. Spines remain scale-like, with rounded tips until ca. the level of the 12 th row, where they become pointed, in that range of rows the spines increase their length to ca. 10 µm. At ca. the level of the 14 th row some columns of spines duplicate, increasing their number to ca. 20 rows at level of the end of the spiny region. Spines from the last rows are shorter (ca. 4 µm) and pointed. Cuticle markedly annulated in the spiny region (annuli ca. 5 µm in length), further down this region the annuli become shorter (ca. 1 µm) and less marked. Lateral alae well-developed, extend from a short distance after the end of the spiny region (ca. 30 µm) to the level of the vulva. One cuticular, slightly curled, barely prominent lip surrounding the triradiate oral opening. Head bearing eight slightly ellipsoidal cephalic papillae (larger diameter/shorter diameter ratio ca. 1.3) arising from the external edge of the lip. Cephalic papillae are almost equidistant, separated from each other by a distance of ca. 4 µm. Amphids lateral, their opening reniform and located at a small cuticular protuberance at level of the external edge of the lip. First cephalic annule comparatively long, truncate, with convex margins and set-off from the head by a marked groove. Stoma short and wide, surrounded by an oesophageal collar, barely extending beyond the level of the first cephalic annule. Oesophagus consists of a muscular, sub-cylindrical procorpus, its base slightly expanded (ca. twice as wide as the anterior region), well differentiated from the short, cylindrical isthmus. Basal bulb rounded, valve-plate welldeveloped. Intestine simple, sub-rectilinear, its fore region slightly dilated, formed by a single layer of large, polygonal cells. Rectum comparatively long. Anus not prominent. Nerve ring encircling procorpus at ca. 45% of its length. Excretory pore ventral, located at ca. 0.7 body-widths posterior to the basal bulb. Vulva a median transverse slit located near the midbody, its lips slightly prominent. Vagina muscular, forwardly directed. Genital tract didelphic-amphidelphic, both ovaries reflexed. Distal end of the anterior ovary reflexed posterior to the excretory pore, distal flexure ca. 1.5 body-widths long. Distal end of the posterior ovary reflexed at ca. 2.5–3 body-widths before the level of the anus, distal flexure ca. 1–1.5 body-widths long. Oocytes in single rows. A fusiform spermatheca present in the posterior uterus, near the level of the basal end of the anterior ovary. Such spermatheca is absent in the anterior branch of the genital tract. Eggs ellipsoidal, smooth-shelled. Gravid females with 1– 6 eggs at a time in the uterus (more frequently two eggs). Tail conical, subulate, ending in a fine tip.

Male. Unknown.

Remarks. Morffe & García (2010) described L. magnum based on light microscopy observations. In their description the authors mentioned the presence of eight small, paired cephalic papillae in the head. The current SEM studies show that the cephalic papillae are not paired but almost equidistant. Such arrangement is a feature quite uncommon in Hystrignathidae since most of the taxa studied by SEM or with light microscopy that included en face views show paired papillae (i.e. Hunt 1981, 1982; Van Waerebeke & Remillet 1982; Morffe & García 2013a, b; Morffe et al. 2015; 2018a, b). Line drawings of Van Waerebeke (1973) show Malagasian species of Artigasia Christie, 1934 with the cephalic papillae widely spaced, giving an equidistant appearance: i.e. A. andringitrae Van Waerebeke, 1973 ; A. dispar Van Waerebeke, 1973; A. lata Van Waerebeke, 1973 and A. semialata Van Waerebeke, 1973 .

The presence of a spermatheca in the posterior uterus was not observed in the original description of the species ( Morffe & García 2010). This structure has not been previously recorded in Hystrignathidae but it has been noted in species from the Thelastomatidae and Travassosinematidae , such as Desmicola skrjabini Adamson, 1984 (Thelastomatidae) and Travassosinema claudiae Morffe & Hasegawa, 2017 ( Adamson 1984; Morffe & Hasegawa 2017). These authors recorded the presence of a sac-like seminal receptacle in the posterior uterus of both species. The pinworm nematodes (Oxyuridomorpha) are quite unique by their haplodiploid reproduction, with diploid females that originate from fertilized eggs and haploid males derived from unfertilized eggs ( Adamson 1994). Adamson (1984) attributed the existence of a single spermatheca as a mechanism for regulating sex ratios, since presumably, the posterior branch of the genital tract (with the spermatheca) could produce fertilized eggs and the anterior branch (without spermatheca) could only produce unfertilized eggs. This could assure the presence of both, females and males among the progeny.

At present, L. magnum is only known from its type locality: Escaleras de Jaruco, Mayabeque province in Western Cuba ( Morffe & García 2010). Therefore, all the populations currently studied constitute new locality records. Viñales, Pinar del Río province is the westernmost record. The population from Sierra de Casas, Isla de la Juventud is the only known location outside of the main island of the Cuban archipelago. The records from Topes de Collantes, Sancti Spíritus province and Sierra de Cubitas, Camagüey province extends the distribution of the species to Central Cuba, the latter being the easternmost. The individuals from the aforementioned new localities coincide morphologically and morphometrically ( Table 2) with the type specimens of the species.

DNA studies. ML and BI analyses were performed for the D2-D3 LSU rDNA, the 18S SSU rDNA and a concatenated dataset of both markers. The trees of the latter dataset were the ones with the highest values of bootstrap support. Since the topology of both ML and BI trees was identical only the former is shown ( Fig. 3 ).

L. magnum is sister taxon to Hystrignathus rigidus Leidy, 1850 in a strongly supported monophyletic clade. Such an arrangement is also supported by the morphological similarities between these species. Both, L. magnum and H. rigidus present opposite rows of spines that are scale-like and pointed, respectively. Also, the female genital tract is didelphic-amphidelphic in these taxa.

The clade formed by the two Longior Travassos & Kloss, 1958 species is situated basally to the clade of Lepidonema + Hystrignathus . This arrangement is supported by the morphological differences between Longior and the two latter genera: unarmed vs. spiny cervical cuticle, digitiform vs. rounded cephalic papillae and monodelphic-prodelphic vs. didelphic-amphidelphic genital tract. Additionally, the procorpus of Longior is cylindrical and elongated whereas it is claviform in Hystrignathus Leidy, 1850 and sub-cylindrical in Lepidonema .

Coynema poeyi (Coy, García & Álvarez, 1993) is located basal to the clade formed by the aforementioned hystrignathid species. This result is consistent with Morffe et al. (2018b) for the D2-D3 domains of the 28S LSU rDNA. As discussed by Morffe et al. (2018b), Coynema presents several characteristic features that differentiated this taxon from the rest of the genera included in the analysis, namely paired and elliptic cephalic papillae arranged in a V-like pattern, the sub-cylindrical procorpus with a basal dilation and the anterior region of the intestine inflated, forming a sac-like structure.

Figures

FIGURE 1. Lepidonema magnum Morffe & García, 2010. Female. A. Oesophageal region, ventral view. B. Tail, ventral view. C. Cephalic end, optical section. D. Cephalic end, external view (reconstructed from SEM images). E. Cephalic end, en face view (reconstructed from SEM images). F. Spines near the end of the spiny region. G. Genital tract, ventral view. H. Habitus, ventral view.

FIGURE 2. Lepidonema magnum Morffe & García, 2010. Female. SEM images. A. Cephalic end, en face view. B. Cervical region. C. End of the spiny region and beginning of the lateral alae. D. Habitus, lateral view. Scale bars: A. 30 µm. B, C. 50 µm. D. 500 µm.

FIGURE 3. Maximum likelihood (ML) tree inferred from the concatenated dataset of the D2-D3 28S LSU rDNA and 18S SSU rDNA for several species of the family Hystrignathidae (Nematoda: Oxyuridomorpha). Travassosinema claudiae (Travassosinematidae) was used as outgroup taxon. Values at the nodes correspond to bootstrap resampling/posterior probability.