Rhabdochona kisutchi Margolis, Moravec & McDonald, 1975

Arai, Hisao P. & Smith, John W., 2016, Guide to the Parasites of Fishes of Canada Part V: Nematoda, Zootaxa 4185 (1), pp. 1-274 : 73-76

Rhabdochona kisutchi Margolis, Moravec & McDonald, 1975

Description (after Margolis et al. 1975). With characteristics of the genus.

Medium-sized worms with rudimentary pseudolabia. Mouth opening roughly hexagonal. Two fairly large lateral amphids and eight small submedian cephalic papillae arranged in an inner and outer circle of four each; papillae of inner circle at mouth margin. Prostom funnel-shaped with distinct basal teeth, and its anterior margin with 10 conical teeth ( Fig. 47 A,B). Vestibule relatively long, straight (but S-shaped in specimens that the authors claim to be “older’). Deirids medium-sized, bifurcate, located near mid-point of vestibule ( Fig. 47 B). Tail of both sexes “ending in blunt point”.

Males (11 specimens, allotype in parentheses): 6.61–8.41 (6.90) long, 0.110–0.150 (0.150) maximum width. Prostom 0.024–0.027 (0.024), vestibule including prostom 0.108–0.153 (0.123), muscular oesophagus 0.225– 0.270 (0.233) and glandular oesophagus 1.35–2.29 (1.69) long. Deirids 0.060–0.075 (0.066), nerve ring 0.168– 0.240 (0.195) and excretory pore 0.249–0.351 (0.286) from anterior end. Subventral pre-cloacal papillae variable in number: allotype has nine on each side, paratypes with the combinations 7+8, 8+8, 8+9, 7+9, 8+10, and 10+10. Additional pair of lateral pre-cloacal papillae at level of 3rd subventral pair or slightly posterior to it. One paratype had two pairs of lateral papillae. Six pairs of post-cloacal papillae—five subventral and one lateral ( Fig. 47 C). Left

spicule 0.564–0.660 (0.627) long, with shaft representing about its distal half; proximal end slightly widened, distal

tip lanceolate, with wide cuticular membrane; ventral process seen on distal tip when spicule protruding from

cloacal opening ( Fig. 47 D). Right spicule variable in shape, 0.087–0.135 (0.120) long; dorsal barb feebly

developed, usually indistinct, its apparent presence depending perhaps on angle from which it is viewed. Length

ratio of right to left spicule 1:4.80 to 1:6.48 (1:5.22). Tail 0.300–0.390 (0.360) long, “ending in blunt point”.

Females (nine specimens, holotype in parentheses): gravid worms 12.04–17.38 (13.59) long, 0.190–0.272 (0.231)

maximum width. Prostom funnel–shaped 0.030–0.036 (0.033), vestibule including prostom 0.126–0.198 (0.192),

muscular oesophagus 0.285–0.361 (0.330), and glandular oesophagus 2.34–3.36 (2.87) long. Deirids 0.060–0.096

(0.090), nerve ring 0.174–0.276 (0.261) and excretory pore 0.411–0.420 (0.411) from anterior end. Tail 0.351–

0.450 (0.351) long, ending in “a blunt point”. Vulva slightly post-equatorial located 6.16–8.02 (6.25) from

posterior end. Amphidelphic. Mature eggs oval, embryonated, always with gelatinous “formations” most often in

shape of caps or lobes covering egg poles and partly their lateral surfaces; rarely polar “formations” tendril-shaped

and as long as 0.045; in some eggs a long filiform filament, about 0.45 long, arises from proximo-lateral corner of

one polar cap ( Fig. 47 E,F,G). Eggs, excluding polar “formations”, “0.039–0.042 x 0.024 (0.039–0.042 x 0.024)

[sic]”, polar caps usually 0.006–0.009 high.

Sites: intestine, pyloric caeca

Hosts: Oncorhynchus kisutch (1); Oncorhynchus mykiss (2, 3); Oncorhynchus nerka (2, 3); Prosopium williamsoni (2, 3); Salvelinus malma (2, 3, 4)

Distribution: British Columbia

Records: 1. Margolis et al. 1975; 2. Anon. 1978; 3. Arai & Mudry 1983; 4. Anon. 1984

Figures

FIGURE 47. Rhabdochona kisutchi Margolis, Moravec & McDonald, 1975. A. female, en face view; B. female, anterior end, dorsal view; C. male, posterior end, ventral view; D. left spicule, distal tip; E. and F. variation in shape of polar “ formations ” on eggs; G. egg with polar filament (truncated). (Redrawn from Margolis et al. 1975)