Rhabdochona cascadilla Wigdor, 1918

Arai, Hisao P. & Smith, John W., 2016, Guide to the Parasites of Fishes of Canada Part V: Nematoda, Zootaxa 4185 (1), pp. 1-274 : 68-70

Rhabdochona cascadilla Wigdor, 1918

Synonyms: Rhabdochona sp. of Bangham (1941 partim); Rhabdochona sp. of Bangham & Venard (1946 partim)

Description (after Byrne 1992a). With characteristics of the genus. General characteristics: outer circle of four cephalic papillae and inner circle of four labial papillae present. Prostom armed with 14 longitudinal sclerotized rods projecting anteriorly as teeth, of which three are dorsal, three ventral, two pairs ventro-lateral, and two pairs dorso-lateral. Sclerotized protuberances present in basal part of prostom [= basal teeth?]. Deirids small, bifurcate, located about the midpoint of vestibule.

Male paratypes (means with ranges in parentheses): body 4.5 (4.0–5.1), prostom 0.016 (0.012–0.019), vestibule 0.076 (0.068–0.085), muscular oesophagus 0.159 (0.146–0.227) and glandular oesophagus 1.1 (0.8–1.8) long. Deirids 0.047 (0.039–0.054), nerve ring 0.124 (0.118–0.134) and excretory pore 0.198 (0.182–0.210) from anterior end. Caudal papillae digitiform: 14 to 19 pre-cloacal and 12 (six pairs) post-cloacal, mostly subventral.

Phasmids minute, located just distal to most posterior pair of caudal papillae. Left spicule 0.378 (0.320–0.415), its alate portion (blade) 0.171 (0.153–0.190) long. Right spicule 0.118 (0.103–0.128) long, with dorsally projecting barb at distal end, and a bulbous, convex proximal end. Length ratio of right to left spicule 1:3.20 (1:3.11 to 1:3.24). Tail 0.277 (0.212–0.322) long, tapering and ending in pointed tip ( Fig. 43 A,B).

Female paratypes (means with ranges in parentheses): body 8.4 (6.4–9.9), prostom 0.024 (0.019–0.027), vestibule 0.089 (0.076–0.097), muscular oesophagus 0.198 (0.175–0.227) and glandular oesophagus 1.4 (1.1–1.6) long. Deirids 0.055 (0.050–0.062), nerve ring 0.147 (0.134–0.159) and excretory pore 0.235 (0.200–0.266) from anterior end ( Fig. 43 C,D). Vulva near midpoint of body, 4.4 (3.5–5.0) from anterior end ( Fig. 43 E). Phasmids minute, posterior to midpoint of tail. Eggs ovoid, smooth, without filaments or floats ( Fig. 43 F), 0.017 (0.017–

0.019) x 0.033 (0.031–0.034). Tail 0.228 (0.184–0.287) long, tapering and ending in pointed tip.

Comments: the 41 fish species listed below have been reported as hosts of R. cascadilla in Canada. However,

according to Byrne (1992a) the numerous reports of this rhabdochonid species “across much of Canada and the

United States, from at least 64 species of fish ( Byrne 1989) should be accepted with reservation”.

Site: intestine

Hosts: Acipenser fulvescens (7, 20, 22); Acrocheilus alutaceus (6); Ambloplites rupestris (1); Ameiurus nebulosus (4); Carpiodes cyprinus (1); Catostomus catostomus (6, 10, 13); Catostomus commersonii (4, 9, 10, 13); Catostomus macrocheilus (6); Couesius plumbeus (6); Culaea inconstans (17); Cyprinella spiloptera (1); Etheostoma exile (5, 7, 8); Etheostoma nigrum (5, 7, 8); Hiodon tergisus (1); Lota lota (8); Luxilus cornutus (2, 3, 5, 7, 16, 17, 18, 19); Margariscus margarita (2, 3, 4); Micropterus dolomieu (3); Moxostoma macrolepidotum (1); Mylocheilus caurinus (6, 12, 14); Nocomis biguttatus (18, 19); Notemigonus crysoleucas (23); Notropis anogenus (8); Notropis hudsonius (1, 5, 7, 8); Notropis stramineus (1); Notropis volucellus (1); Oncorhynchus clarkii (6); Oncorhynchus mykiss (6); Oncorhynchus nerka (6, 9, 17); Perca flavescens (9); Percopsis omiscomaycus (9); Chrosomus eos (3, 21); Prosopium williamsoni (6); Pimephales notatus (3, 5, 7); Ptychocheilus oregonensis (6, 12, 14); Rhinichthys atratulus (8); Rhinichthys cataractae (6); Richardsonius balteatus (6, 12, 14); Salvelinus fontinalis (4, 11); Semotilus atromaculatus (2, 3, 4, 5, 7, 15, 17); Semotilus corporalis (3)

Distribution: Alberta, British Columbia, Hudson Bay Drainage, Manitoba, Nova Scotia, Ontario, Quebec

Records: 1. Bangham & Hunter 1939 (ON); 2. Bangham 1941 (ON); 3. Bangham & Venard 1946 (ON); 4. Choquette 1951a (QC); 5. Bangham 1951 (ON); 6. Bangham & Adams 1954 (BC); 7. Bangham 1955 (ON); 8. Dechtiar 1972a (ON); 9. Collins & Dechtiar 1974 (ON); 10. Leong 1975 (AB); 11. Mudry & Anderson 1977 (AB); 12. Anon. 1978 (BC); 13. Leong & Holmes 1981 (AB); 14. Arai & Mudry 1983 (BC); 15. Mackie et al. 1983 (ON); 16. Byrne & Baker 1987 (ON); 17. Dechtiar et al. 1988 (ON); 18. Byrne 1992a (ON); 19. Byrne 1992b (ON); 20. Choudhury & Dick 1993 (MB); 21. Dubois et al. 1996 (QC); 22. Choudhury & Dick 1998 (HBD, MB); 23. Forest & Cone 2011 (NS)

Figures

FIGURE 43. Rhabdochona cascadilla Wigdor, 1918. A. male, posterior end, lateral view; B. right spicule, lateral view; C. female, head, lateral view; D. female, anterior end, lateral view; E. vulva, vagina and distal uterus, lateral view; F. embryonated egg. (Redrawn from Byrne 1992 a)