Spinitectus polli Campana-Rouget, 1961

Moravec, František & Jirků, Miloslav, 2017, Some nematodes from freshwater fishes in central Africa, Folia Parasitologica (033) 64, pp. 1-39 : 32-36

Spinitectus polli Campana-Rouget, 1961 Figs. 27–29

Syn.: Spinitectus zambezensis Boomker, 1993

Description. Small, whitish nematodes. Body elongate; cephalic end blunt, posterior end conical. Surface of body with transverse rings of spines; rings interrupted at both sides of body by lateral lines ( Figs. 27C , 28A,B,D ); some more posterior rings incomplete. First 2 rings of spines closer to each other than subsequent rings. First ring with 40–61 spines ( Figs. 27C , 28B,D ). Largest spines present in anterior second–fourth ring; first 4–6 anterior rings of spines usually elevated; spines gradually diminishing posteriorly. Female body with spines up to posterior extremity ( Figs. 27F,G , 29C ); spination of male visible only at oesophageal region. Oral aperture oval, dorsoventrally elongated, surrounded by 2 low, large labia, 1 dorsal and 1 ventral, with broad base ( Figs. 27C,D , 28A–E ), forming dorsal and ventral margins of oral opening. One simple, narrow, bent sclerotised structure (sublabium), with a somewhat thickened free margin, attached by its base to inner surface of each labium. Lateral pseudolabia rather large, projecting anteriorly beyond labia. In apical view, flat inner parts of pseudolabia covering partly oral opening somewhat dorsoventrally expanded to form small dorsolateral and ventrolateral extensions. Inner margins of both pseudolabia dorsoventrally straight, parallel to each other ( Figs. 27C,D , 28A–C ). Narrow, inner part of each pseudolabium continues posteriorly into thickened pulp bearing 2 elongate submedian cephalic papillae, small lateral amphid and 3 small, dorsoventrally arranged pores ( Figs. 27C,D , 28C ). Vestibule fairly long, thin-walled, with distinct anterior prostom in lateral view ( Fig. 27A,B ). Deirids not found. Oesophagus clearly divided into anterior muscular and much longer and somewhat wider posterior portion; length ratio of both portions 1: 4.3–4.8 ( Fig. 27A,B ). Nerve ring encircles muscular oesophagus at level between second and fourth rings of spines. Excretory pore situated at level of fourth ring of spines ( Fig. 27A,B ). Tails of both sexes conical.

Male (one specimen). Length of body 5.0 mm, maximum width 177. Maximum length of spines 6. First ring of spines situated 105 from anterior extremity. Number of spines in first ring 49. Length of vestibule including prostom 78. Muscular oesophagus 213 long, 24 wide; glandular oesophagus 911 long, 75 wide; length ratio of both parts of oesophagus 1: 4.3. Length of entire oesophagus and vestibule represent 24% of body length. Nerve ring and excretory pore 147 and 195 from anterior extremity, respectively. Posterior end of body ventrally curved, provided with well-developed subventral alae. Ventral precloacal ridges (area rugosa) well developed, formed by several (up to 6) longitudinal rows of elevated longitudinal cuticular outgrowths ( Figs. 27H,I , 28F,G , 29A,B ). Preanal papillae: 4 pairs of subventral pedunculate, equally spaced papillae. Adanal papillae: 1 pair. Postanal papillae: 4 pairs of subventral papillae and 1 pair of small ventral papillae ( Figs. 27E,H,I , 28G , 29A,B,D ). Large (left) spicule narrow, 705 long, with slightly distended tip provided with small cuticular membrane; length of its shaft 381 (54% of whole spicule length). Small (right) spicule narrow, 99 long ( Fig. 27E,H ). Length ratio of spicules 1: 7.1. Tail 84 long, with small digital mucron at tip.

Female (3 gravid specimens). Length of body 5.5– 6.1 mm, maximum width 190–218. Maximum length of spines 6–9. First ring of spines 96–105 from anterior extremity; postoesophageal region of body including tail with minute, sparsely distributed cuticular spines. Number of spines in first ring 55 in one specimen. Length of vestibule including prostom 75–84; prostom 15–21 long and 21–30 wide. Length of entire oesophagus and vestibule represent 24% of body length. Muscular oesophagus 225– 243 long, 24–27 wide; glandular oesophagus 1.0– 1.1 mm long, 66–90 wide; length ratio of both parts of oesophagus 1: 4.5–4.8. Nerve ring and excretory pore 108–129 and 186–204 from anterior extremity, respectively. Vulva not protruding, situated in posterior part of body at 4.19– 4.77 from anterior extremity (at 74–80% of body length), 1.0– 1.4 mm anterior to anus ( Fig. 27G ). Vagina muscular, directed anteriorly from vulva. Amphidelphic. Fully developed eggs in uterus oval, thick-walled, smooth, larvated; size (n = 10) 39–45 × 24–30 ( Fig. 27J ). Tail conical, 54–69 long, covered by irregularly distributed minute cuticular spines ( Figs. 27F , 29C ).

Host: Clown squeaker Synodontis decorus ( Siluriformes : Mochokidae).

Site of infection: Stomach.

Locality: Sangha River adjacent to Sangha Lodge , 02°59'06''N; 16°13'59''E (Congo basin), DSPA, Central African Republic (collected 11 September 2012).

Prevalence and intensity: 1 fish infected/3 fish examined; 5 nematodes.

Deposition of voucher specimens: IPCAS N-1081.

Remarks. The general morphology of the present specimens is, more or less, in agreement with available descriptions of S. polli , a parasite of squeakers ( Synodontis spp. ) (see Campana-Rouget 1961, Boomker 1993, Moravec and Van As 2015b). The only difference is a somewhat longer left spicule (705 µm vs 366–500 µm), which may be considered to be within intraspecific variability. According to Moravec (1979), the length of the left spicule (663– 1,068 µm) in Spinitectus inermis (Zeder, 1800) , a parasite of European eels, depends on the body size of the male, so that the maximum length of this spicule represents more than 160% of the minimum length.

Based on SEM examination, Moravec and Van As (2015b) reported six pairs of postanal papillae in S. polli from S. nigromaculatus in Botswana, of which the first pair was situated very closely posterior to the posterior edge of the cloacal aperture. The same pair of papillae in the only available male of the present material is located at the level of the cloaca, so it is reported as the adanal pair. Based on LM studies, Campana-Rouget (1961) illustrated these papillae in S. polli at the level of the cloaca and Boomker (1993) as slightly posterior to the cloaca in conspecific nematodes (reported as S. zambezensis ) from South Africa. However, these differences are negligible, within intraspecific variability, and may be associated, with the body size of the nematode or the way of fixation. Usually, six pairs of postanal papillae are reported for Spinitectus spp. , even though the first pair may be in an adanal position in some species (e.g. S. inermis ).

Spinitectus polli has so far been reported from the Democratic Republic of the Congo, Botswana and South Africa ( Campana-Rouget 1961, Boomker 1993, 1994, Boomker and Puylaert 1994, Moravec and Van As 2004, 2015b). The finding of this species in S. decorus in the Central African Republic represents new host and geographical records.

Figures

Fig. 27. Spinitectus polli Campana-Rouget, 1961 from Synodontis decorus Boulenger.A – anterior end of gravid female, lateral view; B – same, higher magnification; C – cephalic end of male, apical view; D – mouth, apical view; E – tail of male, lateral view; F – tail of female, ventral view; G – posterior end of female, lateral view; H – posterior end of male, lateral view; I – caudal end of male, ventral view; J – egg.

Fig. 28. Spinitectus polli Campana-Rouget, 1961 from Synodontis decorus Boulenger, scanning electron micrographs. A – anterior end of male, sublateral view; B – cephalic end of male, apical view; C – mouth, apical view (arrow indicates three pores); D – cephalic end of female, apical view (pseudolabia destroyed); E – anterior end of body, sublateral view; F – posterior end of male with distinct ventral precloacal cuticular ridges; G – caudal end of male, ventral view. Abbreviations: a – amphid; b – cephalic papilla; c – sublabium; d – pseudolabium; e – cloaca.

Fig. 29. Spinitectus polli Campana-Rouget, 1961 from Synodontis decorus Boulenger, scanning electron micrographs. A, B – caudal end of male, sublateral and subventral views, respectively; C – tail of female, ventrolateral view; D – distal end of male tail, ventral view. Abbreviations: e – cloaca; f – anus.