Falcaustra piscicola ( von Linstow, 1907 ) Campana-Rouget, 1961

Moravec, František & Jirků, Miloslav, 2017, Some nematodes from freshwater fishes in central Africa, Folia Parasitologica (033) 64, pp. 1-39 : 5-8

Falcaustra piscicola ( von Linstow, 1907) Campana-Rouget, 1961

Figs. 4 , 5

Syns.: Nematoxys piscicola von Linstow, 1907 ; Spironoura congolense Taylor, 1925

Description. Medium-sized, fusiform, whitish nematodes. Cuticle finely transversely striated. Lateral alae absent. Deirids well developed, rounded, situated at about mid-level of oesophagus ( Fig. 4A,B,J ). Oral aperture large, triangular, surrounded by 3 small lips, each bearing 2 cephalic papillae; pair of lateral amphids present ( Figs. 4D , 5A,B,D ). Buccal cavity supported by flat cuticularised ring ( Fig. 4A,B ). Oesophagus consists of short, muscular pharyngeal portion, long corpus, inflated isthmus forming pre-bulb, and bulb ( Fig. 4A–C ). Nerve ring encircling oesophageal corpus at about 1/4 of way along its length, excretory pore near level of junction of corpus and pre-bulb. Anterior end of intestine expanded. Tail of both sexes conical, sharply pointed ( Figs. 4E,G–I , 5C,F ).

Male (5 specimens). Length of body 13.8–18.7 mm, maximum width 762–1,061. Lips 54–68 long; width of cephalic end at level of lips 177–190. Length of entire oesophagus 2.0– 2.5 mm; length of pharynx 82–95, of corpus 1.5–1.8 mm, of pre-bulb 204–258, of bulb 258–313; width of pharynx, corpus, pre-bulb and bulb 95–109, 136–150, 150–190 and 313–367, respectively. Nerve ring 422–449, excretory pore 1.4–1.9 mm and deirids 1.0– 1.5 mm from anterior extremity. Posterior end of body curved ventrally. Caudal alae absent. Ventral precloacal sucker absent; ventral precloacal region of body with ca 40 pairs of oblique muscle bands ( Fig. 4G ). Nine pairs of genital papillae present, of which 3 subventral pairs are preanal, there is 1 adanal pair and 5 pairs (3 subventral and 2 lateral) are postanal; 1 additional unpaired median papilla present anterior to cloaca; phasmids situated anterior to level of last but one subventral pair of postanals ( Figs. 4E,G,I , 5C,E,F ). Spicules equal, alate, slightly curved, 594–780 long ( Fig. 4E,G ). Gubernaculum well developed, 180–204 long. Tail 120–558 long.

Female (5 gravid specimens). Length of body 17.8– 22.2 mm, maximum width 1.0– 1.3 mm. Lips 54–68 long; width of cephalic end at level of lips 190–218. Length of entire oesophagus 2.5 mm; length of pharynx 95–109, of corpus 1.8–1.9 mm, of pre-bulb 231–245, of bulb 313–326; width of pharynx, corpus, pre-bulb and bulb 122, 136–150, 163–204 and 340–394, respectively. Nerve ring 490–544, excretory pore 1.7–1.9 mm and deirids 1.3–1.5 mm from anterior extremity. Vulva postequatorial, situated 10.5– 13.2 mm from anterior extremity (at 59–60% of body length); vagina muscular, narrow, directed anteriorly from vulva. Eggs numerous, oval, thin-walled, 84–102 × 60–66; content of eggs in uterus uncleaved ( Fig. 4F ). Tail 503–585 long, bearing lateral pair of phasmids ( Fig. 4H ).

Host: Longsnout distichodus Distichodus lusosso Schilthuis ( Characiformes : Distichodontidae ).

Site of infection: Intestine.

Locality : Sangha River adjacent to Sangha Lodge, 02°59'06''N; 16°13'59''E (Congo basin), DSPA, Central African Republic (collected 14 September 2012) .

Prevalence and intensity: 1 fish infected/1 fish examined; 33 nematodes.

Deposition of voucher specimens: IPCAS N-1136.

Remarks. This species was originally described as Nematoxys piscicola from Distichodus sp. in the Cameroon ( von Linstow 1907). Later Inglis (1959) re-studied its type specimens and transferred this species to Spironoura Leidy, 1856 . He found these to be indistinguishable from Spironoura congolense , a species reported from an unidentified fish in the present Democratic Republic of the Congo ( Taylor 1925), which became a junior synonym of S. piscicola . Spironoura is now considered by most authors a genus dubium and all species listed in it are reported in Falcaustra Lane, 1915 (see Anderson et al. 2009).

The morphology of present specimens is more or less in agreement with the descriptions of F. piscicola by von Linstow (1907) and Taylor (1925); they were collected from a congeneric host in the same or nearby regions and, therefore, they are considered to belong to F. piscicola . The present study, which included the first use of SEM for observing F. piscicola , made it possible to solve problems on the description of number of postanal papillae: whereas von Linstow (1907) observed four pairs and Taylor (1925) reported eight papillae on either side or eight to nine papillae on the right-hand side and seven on the left, the present results confirmed six pairs of caudal postanal papillae (including phasmids) in F. piscicola .

In addition to the above-mentioned findings of F. piscicola in the Cameroon and the Democratic Republic of the Congo by von Linstow (1907) and Taylor (1925), this species was recorded from Distichodus brevipinnis Günther and D. rostratus Günther in Lake Chad, Chad ( Vassiliadẻs and Troncy 1974). Accordingly, the present finding of F. piscicola in Distichodus lusosso in the Central African Republic represents new host and geographical records of this species.

Figures

Fig. 4. Falcaustra piscicola (von Linstow, 1907) from Distichodus lusosso Schilthuis. A, B – anterior end of female, lateral and dorsoventral views, respectively; C, D – cephalic end, dorsal and apical views, respectively; E – tail of male, lateral view; F – egg; G – posterior end of male, lateral view; H – tail of female, lateral view; I – tail of male, ventral view; J – deirid.

Fig. 5. Falcaustra piscicola (von Linstow, 1907) from Distichodus lusosso Schilthuis, scanning electron micrographs of male. A, B – cephalic end, sublateral and apical views, respectively; C – tail, subventral view (arrow indicates phasmid); D – detail of mouth, apical view; E – posterior end of body, ventral view; F – tail, ventral view. Abbreviations: a – amphid; b – cephalic papilla; c – lateral postanal papilla; e – median unpaired preanal papilla.