Synodontisia thelastomoides Petter, Vassiliadès et Troncy, 1972

Moravec, František & Jirků, Miloslav, 2017, Some nematodes from freshwater fishes in central Africa, Folia Parasitologica (033) 64, pp. 1-39 : 11

Synodontisia thelastomoides Petter, Vassiliadès et Troncy, 1972

Figs. 8 , 9

Description (based on specimens from S. acanthomias ). Small fusiform nematodes with distinctly transversely annulated cuticle ( Figs. 8A,B,E,F , 9A,C,F ). Narrow lateral alae arise anteriorly somewhat anterior to level of nerve ring and extend posteriorly slightly posterior to level of anus in female and to short distance posterior to median pair of postanal papillae in male ( Figs. 8E , 9C,F ). Oral aperture hexagonal, surrounded by 6 small lip-like formations (2 dorsolateral, 2 ventrolateral and 2 lateral), each of them provided with anteriorly protruding mouth lamella on inner side. Four large, oval submedian cephalic papillae and pair of small amphids present ( Figs. 8C , 9A,B ). Buccal cavity spacious ( Fig. 8A,B ). Oesophagus formed by cylindrical corpus, short isthmus and well-developed bulb; oesophagus opens into intestine through small valve ( Fig. 8A,E,F ). Nerve ring situated at about mid-level of corpus; excretory pore at some distance posterior to oesophagus ( Figs. 8A,E,F ). Tail of both sexes forms very long, slender caudal spike ( Fig. 8D,E,F ).

Male (one specimen). Length of body including caudal spike 1.3 mm, maximum width 150. Buccal cavity 12 long. Entire oesophagus 246 long (18% of body length); corpus 138 long, 33 wide; isthmus 39 long, 33 wide; bulb 69 long, 60 wide. Nerve ring and excretory pore 96 and 408, respectively, from anterior extremity. Testis reaching anteriorly to about level of excretory pore ( Fig. 8F ). Region of cloaca elevated, surrounded by broad oval cuticular mound ( Figs. 8D,F–H , 9C,D ) and bearing 1 pair of large preanal papillae immediately anterior to cloaca and 2 pairs of small postanal papillae ( Fig. 8D,F–H ); large, median ventral caudal lobe bearing somewhat depressed pair of small postanal papillae present 93 posterior to cloacal aperture or 243 anterior to end of tail ( Figs. 8D,F,I , 9C,E ). Spicule simple, well sclerotised, 75 long, with sharply pointed distal tip ( Fig. 8D,F,G ). Tail including slender caudal spike 326 long (24% of body length) ( Fig. 8D ).

Female (one nongravid specimen). Body fusiform; length including caudal spike 1.6 mm, maximum width 218. Buccal cavity 9 long. Entire oesophagus 240 long (15% of body length); corpus 150 long, 39 wide; isthmus 30 long, 39 wide; bulb 60 long, 75 wide. Nerve ring and excretory pore 87 and 285, respectively, from anterior extremity. Vulva 653 from anterior end of body (at 41% of body length); vulval lips not elevated ( Fig. 8E ). Vagina muscular, short, directed anteriorly from vulva. Reproductive apparatus didelphic. Uterus empty ( Fig. 8E ). Tail including slender caudal spike 571 long (36% of body length), provided with pair of minute lateral phasmids located short distance posterior to posterior ends of lateral alae ( Fig. 8E ).

Hosts: Synodontis acanthomias , clown squeaker S. decorus Boulenger , S. greshoffi , blotched upsidedown catfish S. nigriventris David , Congo squeaker S. pleurops Boulenger (all Mochokidae , Siluriformes ) and Xenocharax spilurus Günther ( Distichodontidae , Characiformes ).

Site of infection: Intestine.

Localities: Lower Congo River, right bank near Bulu, Democratic Republic of the Congo, 05°01'30''N; 14°00'25''E ( S. acanthostomias , collected 11 July 2008); Sangha River ( S. decorus , S. greshoffi , S. pleurops , X. spilurus ) and small forest stream ( S. nigriventris ) adjacent to Sangha Lodge, 02°59'06''N; 16°13'59''E ( Congo basin), DSPA, Central African Republic (collected 11–14 September 2012).

Prevalence and intensity: S. acanthomias : 1 fish infected/4 fish examined; 2 nematodes. S. decorus : 1/3; 8. S. greshoffi : 6/9; 1–10. S. nigriventris : 1/2; 1. S. pleurops : 1/3; 9. X. spilurus : 1/1; 12.

Deposition of voucher specimens: IPCAS N-1142.

Remarks. The morphology and measurements of present specimens correspond more or less to the original description of S. thelastomoides provided by Petter et al. (1972) and, accordingly, they are assigned to this species. The present and first SEM observation of S. thelastomoides revealed more details of some features that are hardly visible using light microscopy (LM), mainly regarding the structure of the cephalic end and of the male cloacal region including the caudal papillae.

Synodontisia thelastomoides has so far been reported from Synodontis nigrita , S. ocellifer , S. sorex (type host) and S. zambezensis in Senegal, Chad, Benin and South Africa ( Petter et al. 1972, Vassiliadẻs and Troncy 1974, Vassiliadẻs 1976, Boomker 1994, Dougnon et al. 2012). In South Africa, this species was recorded by Boomker (1994) from S. zambezensis , but no morphological data were provided. Considering the geographical region, it may well be that his nematodes belonged in fact to S. okavangoensis Moravec et Van As, 2004 , a parasite of Synodontis nigromaculatus in nearby Botswana; this congeneric species was described only ten years later ( Moravec and Van As 2004). In contrast to S. thelastomoides , the cephalic papillae of S. okavangoensis are crescent-shaped. The present finding of S. thelastomoides in S. acanthomias in the Democratic Republic of the Congo and those from S. greshoffi , S. decorus , S. nigriventris , S. pleurops and X. spilurus in the Central African Republic represent new host and geographical records of this nematode species.

Figures

Fig. 8. Synodontisia thelastomoides Petter, Vassiliadẻs et Troncy, 1972 from Synodontis acanthomias Boulenger. A – anterior end of male, lateral view; B, C – cephalic end of male, lateral and apical views, respectively; D – posterior end of male, lateral view; E, F – total view of young female and male, respectively, lateral views; G – spicule, lateral view; H – region of cloaca, ventral view; I – last pair of postanal papillae, sublateral view.

Fig. 9. Synodontisia thelastomoides Petter, Vassiliadẻs et Troncy, 1972 from Synodontis acanthomias Boulenger, scanning electron mi- crographs. A, B – cephalic end of male, apical and lateral views, respectively; C – region of cloaca and anterior part of tail, lateral view; D – region of cloaca, subventral view (arrows indicate subventral and lateral postanal papillae); E – median pair of postanal papillae (see arrows) on ventral caudal lobe situated some distance posterior to cloaca; F – body of male with distinct lateral alae, lateral view. Abbreviations: a – amphid; b – cephalic papilla; c – cephalic lamella; d – genital cone; e – pair of preanal papillae; f – postcloacal region with two pairs of postanal papillae; g – ventral caudal lobe bearing median pair of postanal papillae; h – cloacal aperture.