Oncophora melanocephala (Rudolphi, 1819) Baudin-Laurencin, 1971

Arai, Hisao P. & Smith, John W., 2016, Guide to the Parasites of Fishes of Canada Part V: Nematoda, Zootaxa 4185 (1), pp. 1-274 : 64-66

Oncophora melanocephala (Rudolphi, 1819) Baudin-Laurencin, 1971

Description (after Moravec et al. 1999). With characteristics of the genus. Relatively large worms with elongate body, adult females much longer than males; body of both sexes broadest posteriorly. Cuticle thick with fine, dense transverse striations. Body white, only buccal capsule darkly coloured, almost black. Mouth opening slit-like, formed by two lateral valves, strengthened on inner face by about 20 thin longitudinal thickenings (ribs or ridges) extending posteriorly to its base; a few ridges usually incomplete. Each valve has one dorso-lateral and one ventrolateral cephalic papilla, one small lateral amphid, and two large, longitudinally elongated, sclerotized plates (shields) in outer buccal wall. Dorsal and ventral sides of anterior part of buccal capsule provided with large tridents. Anterior portion of capsule formed by valves followed by shorter and narrower posterior portion of capsule in form of thick-walled ring surrounding spacious buccal cavity ( Fig. 41 A). Posterior margin of this connecting ring followed by small, colourless, oesophageal cup. Oesophagus leads to straight narrow intestine. Small deirids located just behind nerve ring level.

Males (four specimens): 12.9–20.8 long, maximum width 0.245–0.354. Buccal capsule 0.141–0.207, and connecting ring 0.036–0.042 long. Each valve bears about 22 longitudinal ridges, some incomplete. Whole tridents 0.210–0.255 long. Muscular oesophagus 1.1–1.7, glandular oesophagus 1.2–1.6 long. Nerve ring and excretory pore 0.340–0.435 and 0.462–0.465 from anterior end (deirids not located). Posterior end with broad caudal alae supported by pedunculate papillae. Seven pairs of pre-cloacal and five pairs post-cloacal pedunculate caudal papillae. Cloacal opening surrounded by two transverse mounds, forming laterally two pairs of additional papillae ( Fig. 41 B). Right spicule well sclerotized, 0.579–0.843 long; left spicule hardly visible, 0.249–0.294 long. Tail conical, 0.084–0.138 long, sometimes with three poorly developed minute papilla-like outgrowths.

Females (one complete and two incomplete specimens with eggs; range of measurements of three juveniles in parentheses): Gravid worms markedly broad at approximately posterior third, and narrow filiform anteriorly. 53.8 (20.5–33.8) long. Width: anterior to vulva 0.204–0.367 (0.299–0.313), at vulva level 0.680–1.3 (0.258–0.394), at posterior part 0.544–0.898 (0.272–0.435). Buccal capsule 0.198 (0.198–0.204), and connecting ring 0.033 (0.030– 0.033) long. Whole tridents 0.233 (0.219–0.240) long. Muscular oesophagus 1.9 (1.8–1.9), glandular oesophagus 1.8 (1.6–1.8) long. Nerve ring, excretory pore, and deirids 0.326 (0.340–0.394), (0.408–0.449) and 0.422 (0.400) from anterior end. Vulva not elevated, 12.1–18.5 (5.4–9.5) from posterior end of body. Ovijector with sclerotized walls, surrounded by mass of cells. Vagina muscular, narrow, directed posteriorly from vulva. Uterus extends a short distance anterior to vulva; uterus contains eggs (without eggs in juveniles) ( Fig. 41 C). Tail conical, 0.326– 0.462 (0.286) long, with rounded tip bearing three minute, poorly developed papilla-like protrusions.

Site: stomach

Host: Xiphias gladius

Distribution: Atlantic

Record: Hogans et al. 1983

Figures

FIGURE 41. Oncophora melanocephala (Rudolphi, 1819) Baudin-Laurencin, 1971. A. young female, anterior end, dorsoventral view; B. male, posterior end, ventral view; C. young female, vulvar region. (Redrawn from Moravec et al. 1999)