Suifunema Chitwood, 1932

Morffe, Jans, Carreno, Ramon A., Ozawa, Sota, Sriwati, Rina & Hasegawa, Koichi, 2019, On the status of Suifunema peregrinatum (Carreno, 2017) n. comb. (Nematoda: Oxyuridomorpha: Thelastomatidae) and first record of the species for Japan, Zootaxa 4651 (2), pp. 351-365 : 353-363

Suifunema Chitwood, 1932

Generic diagnosis (emended). Female. Body robust, fusiform. Cervical cuticle unarmed. Lateral alae absent. First cephalic annule truncate, slightly dilated. Oesophagus with a muscular corpus, its base clavate, well set-off from the short isthmus. Nerve ring encircling the corpus near its midpoint. Excretory pore post-bulbar. Vulva located in the anterior half of body. Genital tract didelphic-prodelphic. Tail subulate, ending in a fine tip.

Male. Body shorter and more slender than female, posterior end ventrally curved. Lateral alae present. Cephalic cap with smooth cuticle, without distinctive papillar structures. Oesophagus with a muscular, slightly clavate corpus, set-off from the comparatively long isthmus. The corpus and isthmus are similar in length. Nerve ring encircling the isthmus near its midpoint. Excretory pore post-bulbar. Monorchic. Cloaca located in a prominent genital cone. Copulatory papillae arranged as two pre-cloacal and two post-cloacal pairs. First pre-cloacal pair large, lateral, mammiform, located near the level of the cloaca and almost at same level of the second pre-cloacal pair, sub-ventral, mammiform, just anterior to the genital cone. First post-cloacal pair ventral, formed by small papillae close to each other, located at the posterior end of the genital cone. Second post-cloacal pair ventral, located in the first third of the tail filament. Tail filament conical, ending in a fine tip. Single spicule present.

Suifunema peregrinatum ( Carreno, 2017) n. comb.

Fig. 1 A–F, Fig. 2 A–E, Fig. 3 A–G, Fig. 4 A–H

Material examined. Vouchers: 17♀♀, from a lab culture of specimens of Pycnoscelus indicus from Japan, Okinawa prefecture, Ishigaki, Pai Land Hotel, 24°20’21’’N, 124°9’28’’E; 20/ VI /2016 ; S. Ozawa coll.; CZACC 11.7040 – 11.7056. 5♂♂, same data as the latter ; CZACC 11.7057 –11.7061 . 2♀♀, same data as the latter ; NCHL A19 – A20 . 2♂♂, same data as the latter ; NCHL A21 – A22 . 2♀♀, same data as the latter ; CHIOC 38485 a-b. 2♂♂, same data as the latter ; CHIOC 38485 c-d .

Redescription. Female. Body relatively robust, widening from the base of the first cephalic annule, maximum body width at level of the midbody, then tapering towards anus. Cuticle markedly annulated from the end of the first cephalic annule to the level of the anus. Annuli more evident at level of the cervical region, extending approximately to level of the base of corpus. Annuli at the cervical region of ca. 6 µm in width, then increasing their width to ca. 7 µm at the posterior half of body. Lateral alae absent. Head bearing eight paired labiopapillae arranged as two sub-dorsal pairs and two sub-ventral pairs. Labiopapillae are trapezoid-like, with the shortest parallel side in the internal margin of the head and are delimitated by grooves that extend from such internal margin to ca. two thirds of the head-width. Amphids lateral, pore-like, located near the external margin of the head. Buccal aperture rounded, surrounded by an annular labium. First cephalic annule cone-like, truncate, slightly inflated, ca. three head-lengths long. Stoma short, slightly wider than the first portion of the oesophagus, bearing three cuticularized plates, one dorsal and two sub-ventral, projecting from the stoma internal wall to the center of the lumen. Oesophagus consisting of a muscular corpus, with an anterior portion (ca. two thirds of its length) sub-cylindrical and its base clavate, well set-off from the short isthmus. Basal bulb rounded, valve-plate well developed. Intestine simple, sub-recti- linear, its fore region inflated. Rectum short. Anus not prominent, as a crescent-like slit, its convex side anteriorly directed. Nerve ring encircling corpus at about 60% of its length. Excretory pore post-bulbar, located at ca. half of a body-width posterior to basal bulb. The excretory pore is surrounded by an elevated cuticular ring. Vulva a ventral, median transverse slit, displaced to the anterior half of body, its lips slightly prominent. Vagina muscular, anteriorly directed. Genital tract didelphic-prodelphic. Oocytes in single rows. Both ovaries reflexed just behind the excretory pore. Eggs numerous, ellipsoidal, shell ornamented with small punctations, operculum present. Tail subulate, conical, ending in a fine tip. Phasmids pore-like, sub-dorsal, located in the tail, to a short distance (ca. 35 µm) posterior to anus (ca. one seventh of the tail length).

Male. Body shorter and more slender than females. Posterior end ventrally curved. Lateral alae well developed, extending from a distance of ca. 20 µm behind the anterior end of the body (ca. the midpoint of the corpus) to a distance of ca. 20 µm before the cloaca. Bluntly rounded anterior end. Cephalic cap with smooth cuticle, without distinctive papillar structures. Posterior to the cephalic cap the cuticle is annulated until ca. the level of the genital cone. Both annuli, next to the cephalic end and near the genital cone ca. 1 µm in width. Amphids lateral, as crescent-like pores. Oral opening broad, circular, its diameter ca. 2 µm, surrounded by a cuticular ring. Stoma short. Oesophagus with a muscular, slightly clavate corpus, set-off from the comparatively long isthmus. The corpus and isthmus are similar in length, with the corpus ca. 1.6 isthmus lengths. Basal bulb rounded, valve-plate well developed. Intestine simple, its anterior region slightly dilated. Nerve ring encircling the isthmus at ca. the level of its midpoint. Excretory pore located at ca. 1.5 body-widths posterior to the basal bulb. The excretory pore is surrounded by an elevated cuticular ring. Monorchic. Testis outstretched, with vas deferens subdivided into three regions: an anterior with rounded cells; a median, swollen region with granular content and a posterior with large cells and connected to cloaca. Spicule single, sclerotized, almost straight, shaft spindle-shaped, capitulum ventrally bent, rounded and distal tip rounded. Cloaca located on an elevated genital cone. Four pairs of copulatory papillae present, arranged as two pre-cloacal and two post-cloacal pairs. First pre-cloacal pair large, lateral, mammiform, located at ca. 6 µm before the cloaca and almost at same level of the second pre-cloacal pair, sub-ventral, slightly shorter than first pair, mammiform, just anterior to the genital cone. First post-cloacal pair ventral, formed by small papillae positioned close to each other at the posterior end of the genital cone. Second post-cloacal pair ventral, located in the first third of the tail filament (ca. 5 µm of its base), which is conical, ending in a fine tip. Phasmids slit-like, lateral, located a short distance (ca. 3 µm) posterior to the sub-dorsal pair of pre-cloacal papillae.

Differential diagnosis. S. caudelli was described only on the basis of female specimens ( Chitwood 1932). Females of S. peregrinatum n. comb. resemble S. caudelli by having a similar position of the vulva (V% = 28.00– 35.00 vs. 28.00–33.00). They differ by S. peregrinatum n. comb. being longer (body length = 1.725 –3.225 mm vs. 1.250 –1.825 mm) and more slender (a = 8.00–15.00 vs. 6.00–10.35) than S. caudelli . Moreover, the oesophagus is comparatively shorter (b = 6.00–10.00 vs. 5.00–6.00) and the tail is comparatively longer (c = 5.00–8.00 vs. 7.55–11.00) in S. peregrinatum n. comb. The aforementioned morphometrics correspond to the type specimens of S. peregrinatum n. comb. ( Carreno 2017) and the current study of the types of S. caudelli .

The didelphic-prodelphic female genital tract is shared with the genera Cranifera Kloss, 1960 , Bilobostoma Jex, Schneider, Rose & Cribb, 2005 , Blattophila , Davenema Mohagan & Spiridonov, 2017 , and Hammerschmidtiella ( Adamson & Van Waerebeke 1992; Jex et al. 2005; Mohagan & Spiridonov 2017). Cranifera is similar to Suifunema in the shape of the oesophagus, with the corpus slightly clavate and set-off from a short isthmus and the nerve ring encircling the corpus at its midpoint. Both genera can be segregated by the shape of the head end, with the first cephalic annule of Suifunema long and slightly inflated, set-off from the head by a shallow groove. In Cranifera the first cephalic annule is separated from the head by a deep constriction ( Adamson & Van Waerebeke 1992). Blattophila , Davenema , and Hammerschmidtiella are easily differentiated from Suifunema by the form of the oesophagus, with the base of the corpus markedly inflated. Moreover, the cervical region of Davenema and Hammerschmidtiella present wide, marked annuli that are narrower and less marked in Suifunema ( Sriwati et al. 2016; Mohagan & Spiridonov 2017). Bilobostoma has a corpus with a basal dilation similar to Davenema and Hammerschmidtiella and the nerve ring at the level of the isthmus. The nerve ring of Suifunema is located at level of the corpus and also lacks such marked dilation. As a feature unique among the family Thelastomatidae , Bilobostoma and Malaspinanema Jex, Schneider, Rose & Cribb, 2005 , present a bilobed structure in the oral opening ( Jex et al. 2005).

At present, males are known in 27 of the 37 genera of Thelastomatidae , including Suifunema . Males of Suifunema can be differentiated from several thelastomatid genera by having a single spicule. A spicule is absent in Aoruroides Travassos & Kloss, 1958 , Aorurus Leidy, 1849 , Buzionema Kloss, 1966 , Cordonicola Ali & Farooqui, 1969 , Coronostoma Rao, 1958 , Corydiella Rao & Rao, 1965 , Davenema , Galinanema Spiridonov, 1984 , and Golovatchinema Spiridonov, 1984 ( Spiridonov 1984; Adamson & Van Waerebeke 1992; Mohagan & Spiridonov 2017).

From the genera having a spicule, Suifunema differs from Cameronia Basir, 1948 ; Euryconema Chitwood, 1932 and Leidynemella Chitwood & Chitwood, 1934 by having four pairs of copulatory papillae, including one pair in the tail appendage. The aforementioned genera present three pairs of copulatory papillae. Of them, Cameronia and Leidynemella lack a pair on the tail. Also, males of Cameronia present an indistinct isthmus, unlike in Suifunema .

Suifunema can be differentiated from Severianoia (Schwenck, 1926) by the form of the corpus: clavate vs. sub-cylindrical. In Leidynema Schwenck in Travassos, 1929 , males have 3–5 vs. four pairs of copulatory papillae and the tail lacks the longer filiform appendage of Suifunema . Adult males of Tetleyus Dale, 1964 keep the cuticle of the fourth stage larva as a sheet around the body as a unique feature among the family ( Adamson & Van Waerebeke 1992). This feature together with the presence of five pairs of copulatory papillae differentiate this genus from Suifunema .

There are several genera of thelastomatids which, like Suifunema , have a spicule and four pairs of copulatory papillae. These include Cephalobellus Cobb, 1920 , Cranifera , Desmicola Basir, 1956 , Gryllophila Basir, 1942 , Hammerschmidtiella , Johnstonia Basir, 1966 , and Wetanema Dale, 1967 . Of these, Cephalobellus lacks the pair of papillae on the tail appendage and Wetanema possesses two vs. one pair in the tail appendage. The first cephalic annule is evident and well developed in Desmicola and Gryllophila in contrast to Suifunema where this structure is not conspicuous. The corpus of Cranifera presents the base with a sub-spherical dilation vs. the slightly clavate corpus of Suifunema . In Hammerschmidtiella a gubernaculum is present, together with the single spicule vs. Suifunema that lacks a gubernaculum. Johnstonia presents an elevated genital cone bearing one pre-cloacal pair of papillae, one adanal pair and one median duplex post-cloacal pair. Its long, filiform tail appendage presents a pair of papillae. Suifunema presents two pre-cloacal pairs of papillae, one sub-dorsal and one sub-ventral just anterior to the genital cone that only bears one pair of papillae ventral and post-cloacal.

Thelastoma Leidy, 1849 is a different case among the Thelastomatidae , with a spicule being present or absent ( Lee 1974; Baruš & Koubková 2002). The species bearing a spicule can be differentiated by the shape of the oesophagus: sub-cylindrical and diminishing its diameter posteriorly towards the comparatively short isthmus. In Suifunema the corpus is clavate and the isthmus is notably long, almost as long as the corpus. As in Suifunema , Thelastoma species have four pairs of copulatory papillae, but these are in a different arrangement: three pairs in the genital cone: pre-cloacal, adanal and post-cloacal plus a fourth pair in the tail appendage. As described before, the Suifunema genital cone bears a single pair of papillae.

As in Thelastoma , there are males of Blattophila with the spicule present or not. The morphology of the posterior end is different in both genera: the male of S. peregrinatum has a conical tail filament. In Blattophila it is very short and spike-like ( Farooqui 1967). Moreover, an evident genital cone is present in Suifunema , that apparently is absent in Blattophila .

Phylogenetic relationships. The ML and BI trees vary, but the topology of the clade containing S. peregrinatum n. comb. is the same in both phylograms ( Figs. 5 and 6 ). This monophyletic and well supported clade also contains Blattophila sp., Bilobostoma sp., Davenema obtusum Mohagan & Spiridonov, 2017 , three species of Hammerschmidtiella and Malaspinanema sp. This coincides with previous studies using the D2-D3 LSU rDNA ( Spiridonov & Guzeeva 2009). With the exception of Malaspinanema , whose female genital tract is monodelphic, this clade includes genera with a didelphic-prodelphic female genital tract. In addition to the genital tract, those taxa (including Malaspinanema ) also share several features including a robust and fusiform body, vulva located in the first half of body, and a subulate tail. These characters are each important for generic diagnosis.

Suifunema is located basal to a clade formed by Bilobostoma + Hammerschmidtiella + Blattophila + Malaspinanema . This can be justified morphologically by the differences between S. peregrinatum n. comb. with the aforementioned genera, namely the oesophagus with the corpus slightly clavate, without the marked basal dilation characteristic of the other genera. On the other hand, Bilobostoma and Hammerschmidtiella have the first cephalic annule less developed than Suifunema .

Davenema is located basal to the clade formed by Bilobostoma + Hammerschmidtiella + Blattophila + Malaspinanema + Suifunema . This is contradictory, since the morphology of Davenema is more similar to genera like Hammerschmidtiella by the form of the oesophagus and the markedly annulated cervical region.

In both analyses the sister group of the clade described above is monophyletic, formed by Cranifera + Severianoia . These genera also have females with a didelphic-prodelphic genital tract. However, the reason for their arrangement in a separate clade could be the presence of apparent differences with the genera of the other clade. In both Cranifera and Severianoia the vulva is located near the midpoint of the body rather than the anterior half of the body and the corpus is slightly clavate in Cranifera and cylindrical in Severianoia . In Cranifera the first cephalic annule is separated from the head by a deep constriction, a feature absent in the other genera.

Our understanding of the phylogenetic relationships of the family Thelastomatidae is far from complete, since only limited sequences of a few species and genera among the larger group of Thelastomatoidea are available. Several genera are not well characterized and males are still unknown for many of them. In order to improve this, more molecular data is needed. In addition, many taxa need to be properly described.

Remarks. In the original description, S. caudelli was defined as didelphic-amphidelphic by Chitwood (1932). Adamson & Van Waerebeke (1992) followed this criterion for the generic diagnosis. On the basis of the illustration of the original description, the examination of the types of S. caudelli and the material of S. peregrinatum n. comb. we verify that both ovaries in females are anteriorly directed. Thus, the female genital tract of the genus is didelphicprodelphic. Moreover, the males of S. peregrinatum n. comb. are the first described for the genus Suifunema . Due to the aforementioned statements we updated and amended the differential diagnosis including not only the comparison of S. peregrinatum n. comb. with S. caudelli , but also the comparison of Suifunema females with the other didelphic-prodelphic thelastomatoid genera as well these first described males of S. peregrinatum n. comb. with the other males known among Thelastomatidae . These data were not included in the few previous works regarding Suifunema (i.e. Chitwood 1932; Mimioğlu & Şahin 1976; Zervos 1987). Thus, we consider it as an addition to the information on the genus.

Besides the arrangement of the female genital tract the other emendation to the generic diagnosis was the position of the nerve ring. Chitwood (1932) described the location of this structure as “…in the region of the isthmus”. The types of the species show the nerve ring located near the level of the midpoint of the corpus, as in S. peregrinatum n. comb.

The specimens from Japan are morphologically consistent with the populations of S. peregrinatum n. comb. from USA and Galapagos Islands ( Sinnott et al. 2015; Carreno 2017). Only some variables are subtly different, but still falling within the range of the species. In the females ( Table 1 ), the vulva is slightly farther posteriorad in the specimens from Galapagos (V% = 32.30–47.20 vs. 25.81–40.05). The type population of USA slightly differs by the longer body (1.725 –3.225 mm vs. 1.654 –2.337 mm) and tail (290–440 µm vs. 227–346 µm). The basal bulb diameter is also larger (70–101 µm vs. 60–89 µm). In the case of the males ( Table 2 ), both the nerve ring (55–79 µm vs. 41–58 µm) and the excretory pore (109–130 µm vs. 97–119 µm) are farther posterior in the specimens from USA. Both available sequences of S. peregrinatum n. comb. from Japan and USA match with 100% identity in an alignment of 719 bp. The current record constitutes the first for Japan and P. indicus is a new host for the species.

Figures

FIGURE 1. Suifunema peregrinatum (Carreno, 2017) n. comb. (Nematoda: Oxyuridomorpha: Thelastomatidae). Specimen from Okinawa prefecture, Japan. Female. A. Oesophageal region, lateral view. B. Tail, lateral view. C. Cephalic end, optical section. D. Cephalic end, lateral view (reconstructed from SEM images). E. Cephalic end, en face view (reconstructed from SEM images). F. Habitus, lateral view.

FIGURE 2. Suifunema peregrinatum (Carreno, 2017) n. comb. (Nematoda: Oxyuridomorpha: Thelastomatidae). Specimen from Okinawa prefecture, Japan. Male.A. Oesophageal region, lateral view. B. Tail, lateral view. C. Cloacal region, lateral view (reconstructed from SEM images). D. Spicule, lateral view. E. Habitus, lateral view.

FIGURE 3. Suifunema peregrinatum (Carreno, 2017) n. comb. (Nematoda: Oxyuridomorpha: Thelastomatidae). Specimens from Okinawa prefecture, Japan. Female. SEM images. A, B. Cephalic end, lateral view. C. Cephalic end, en face view. D. Excretory pore. E. Vulva. F. Tail end (arrowhead shows the phasmid). G. Anus. Scale bars A, E, F, G. 10 µm. B, C, D. 5 µm.

FIGURE 4. Suifunema peregrinatum (Carreno, 2017) n. comb. (Nematoda: Oxyuridomorpha: Thelastomatidae). Specimens from Okinawa prefecture, Japan. Male. SEM images. A. Habitus, lateral view. B. Cephalic end, lateral view. C. Cephalic end, en face view. D. Excretory pore. E. Tail end, dorso-lateral view. F. Region of the genital cone, dorso-lateral view. G. Tail end, lateral view. H. Tail end, ventro-lateral view. Scale bars: A. 20 µm. C, F. 1 µm. B, E. 5 µm. D, G, H. 2 µm.

FIGURE 5. Maximum likelihood (ML) tree inferred from the D2-D3 LSU rDNA for several species of the family Thelastomatidae (Nematoda: Oxyuridomorpha). Cameronia multiovata (Thelastomatidae) and three species of Travassosinema (Travassosinematidae) were used as outgroup taxa. Values at the nodes correspond to bootstrap resampling (≥70). Newly obtained sequence in bold.

FIGURE 6. Bayesian inference (BI) tree inferred from the D2-D3 LSU rDNA for several species of the family Thelastomatidae (Nematoda: Oxyuridomorpha). Cameronia multiovata (Thelastomatidae) and three species of Travassosinema (Travassosinematidae) were used as outgroup taxa. Values at the nodes correspond to posterior probability (≥0.95). Newly obtained sequence in bold.