Labeonema longispiculatum, Moravec & Jirků, 2017

Moravec, František & Jirků, Miloslav, 2017, Some nematodes from freshwater fishes in central Africa, Folia Parasitologica (033) 64, pp. 1-39 : 2-3

Labeonema longispiculatum sp. n.

Figs. 1 , 2

ZooBank number for species:

urn:lsid:zoobank.org:act:A0737268-7694-4C0E-A65C-0649843FCCA4

Description. Small whitish nematodes with finely transversely striated cuticle; markedly narrow lateral alae arise short distance posterior to anterior extremity, extending posteriorly to about level of anus in both sexes ( Fig. 2A,C ). Mouth triangular, with 3 lips, each provided with cuticular flap overhanging oral aperture; 3 small elongate, slightly sclerotised structures present at inner bases of lips. Four submedian double cephalic papillae (2 on dorsal lip and 1 on each ventrolateral lip) present; pair of large lateral amphids situated near oral aperture on ventrolateral lips ( Figs. 1C , 2A,B ). Oesophagus consists of short pharyngeal portion, long corpus, isthmus and bulb; bulb provided with sclerotised valves ( Fig. 1A,B,E ). Intestine straight. Nerve ring encircles oesophagus approximately at mid-level of corpus. Conspicuous excretory pore situated near posterior end of corpus. Tail of both sexes conical, ending in sharp point ( Figs. 1F–H , 2D–G ).

Male (5 specimens; measurements of holotype in parentheses). Length of body 2.0– 2.5 mm (2.5 mm), maximum width 82–109 (109). Length of entire oesophagus 363–471 (468); length of pharynx 21–33 (33), width 15–18 (15); length of corpus 300–351 (345), maximum width 24 (24); isthmus 30–45 (30) long, 12–18 (12) wide; bulb 54–60 (60) long, 48–60 (57) wide. Nerve ring and excretory pore 156–195 (180) and 270–330 (330), respectively, from anterior extremity. Tail curved ventrally. Caudal alae absent. Caudal papillae rather variable in number and arrangement, sometimes distributed asymmetrically. Preanal papillae: 5–6 pairs of subventral papillae and 1–3 more lateral papillae situated anterior to paired papillae on either side of body; in addition, 3 pairs of minute ventral papillae and 1 unpaired median papilla present on anterior lip of cloaca. Adanal papillae: 1 subventral pair. Postanal papillae: 5–6 pairs, including 3–4 subventral and 2 lateral; pair of small lateral phasmids located slightly anterior to first pair of lateral postanal papillae ( Figs. 1F,G , 2D–G ). Two well sclerotised, equally long spicules present, 210–228 (228), curved ventrally in lateral view; proximal ends obtuse, markedly narrow, distal ends pointed ( Figs. 1F , 2D,F ). Gubernaculum well sclerotised, 45–48 (45) long ( Fig. 1F ). Length ratio of gubernaculum and spicules 1: 4.38–5.07 (1: 5.07). Length of tail 108–138 (138).

Female (5 ovigerous specimens; measurements of allotype in parentheses). Length of body 2.8–2.9 mm (2.9 mm), maximum width 150–163 (150). Length of entire oesophagus 501–519 (519); length of pharynx 27–30 (27), width 15–18 (18); of corpus 366–384 (384), width 27 (27); of isthmus 45 (45), width 18–21 (21), of bulb 60–63 (63), width 60 (60). Nerve ring and excretory pore 204 (204) and 360–363 (363), respectively, from anterior extremity. Vulva in posterior half of body, 2.0 mm (2.0 mm) from anterior extremity [at 69–73% (69%) of body length], with conspicuously elevated posterior lip ( Fig. 1A,D ). Vagina narrow, directed posteriorly from vulva. Ovary near anterior end of uterus ( Fig. 1A ). Uterus didelphic, with posterior branch transformed into sac without ovary and oviduct and extending posteriorly somewhat posterior to level of vulva. Uterus containing 5–6 (6) oval, thin-walled eggs at different stages of development, 153–186 × 111–165 (153–177 × 111–165); no hatched larvae present ( Fig. 1A ). Length of tail 218–245 (245).

Type host: Synodontis acanthomias Boulenger ( Siluriformes : Mochokidae ).

Site of infection: Intestine (distal part).

Type locality: Lower Congo River , right bank near Bulu, Democratic Republic of the Congo, 05°01'30''N; 14°00'25''E (collected 11 July 2008) .

Prevalence and intensity: 3 fish infected/4 fish examined; approximately 950 and 1,000 nematodes (specimens from one of the infected fish not sampled).

Deposition of type specimens: IPCAS N-1140 (holotype, allotype and many paratypes) .

Etymology: The name longispiculatum relates to a characteristic feature of this nematode species, i.e. the presence of very long spicules as compared with congeners.

Remarks. To date, the following five species of Labeonema Puylaert, 1970 have been described from freshwater fishes in Africa: L. africanum Moravec et Van As, 2004 , L. bainae Baker, 1982 , L. bakeri Van Waerebeke, Chabaud, Bain et Georges, 1988, L. intermedium Puylaert, 1970 and L. synodontisi (Vassiliadẻs, 1973) (see Moravec and Van As 2004, Koubková et al. 2008). Although the body measurements of all these species are similar to those of L. longispiculatum sp. n., their spicules are much shorter; the longest spicules (105–120 µm) are found in L. africanum , whereas those of other species are shorter than 100 µm. On the other hand, the spicules of the new species are 210–228 µm, i.e. approximately twice as long as those in L. africanum , a parasite of Synodontis nigromaculatus Boulenger in Botswana ( Moravec and Van As 2004). Both species also differ in the length of the gubernaculum (45–48 µm in L. longispiculatum vs 30–36 µm in L. africanum ), in the gubernaculum/spicules length ratio (1: 4.4–5.1 vs 1: 3.2–3.7) and in the number and distribution of genital papillae; in contrast to L. africanum , the proximal ends of spicules in L. longispiculatum are conspicuously narrowed. Interspecific differences are also found in the structure of the cephalic end.

Besides L. longispiculatum and L. africanum , there is an additional congeneric species, L. synodontisi (syn. Raillietnema synodontisi Vassiliad ẻs, 1973), reported from several species of mochokid catfishes ( Synodontis spp. ) in Chad, Senegal and South Africa, and from aquarium-reared S. eupterus Boulenger in Europe ( Czech Republic) originally imported from Africa (Vassiliadẻs 1973, 1976, Vassiliadẻs and Troncy 1974, Moravec and Řehulka 1987, Boomker, 1994, Koubková et al. 2008). This species can be easily distinguished from L. longispiculatum by much shorter spicules (75–94 µm vs 210–228 µm). Other congeneric species ( L. bainae , L. bakeri and L. intermedium ) are parasites of hosts belonging to other fish families ( Schilbeidae , Distichodontidae and Cyprinidae , respectively).

Figures

Fig. 1. Labeonema longispiculatum sp. n. from Synodontis acanthomias Boulenger. A – general view of female, lateral view; B, C – cephalic end, lateral and apical views, respectively; D – vulva, lateral view; E – anterior end of female, lateral view; F, G – posterior end of male, lateral and ventral views, respectively; H – tail of female, lateral view.

Fig. 2. Labeonema longispiculatum sp. n. from Synodontis acanthomias Boulenger, scanning electron micrographs of male. A – cephalic end, apical view (arrows indicate lateral alae); B – cephalic end, sublateral view; C – anterior end of body, sublateral view (arrow indicates lateral ala); D – posterior end, sublateral view; E – posterior end, lateral view (another specimen); F – posterior end with distinct preanal papillae arranged in two rows, ventral view; G – tail, lateral view. Abbreviations: a – amphid; b – cephalic papilla; c – cloaca.