** Hysterothylacium sp.

Synonym: Thynnascaris sp.

Sites: alimentary tract, body cavity, mesenteries

Hosts: Alosa aestivalis (8, 14); Alosa pseudoharengus (8, 14); Ambloplites rupestris (1); Boreogadus saida (6); Catostomus columbianus (4); Coregonus clupeaformis (4); Cottunculus microps (7); Cottus aleuticus (4); Culaea inconstans (11); Fundulus diaphanus (10); Gadus morhua (3, 9); Gasterosteus aculeatus (10); Lepomis macrochirus (10); Lycodes esmarkii (7); Lycodonus mirabilis (7); Macrourus berglax (7); Mallotus villosus (5); Melanogrammus aeglefinus (9); Merluccius bilinearis (9); Morone americana (10); Nezumia bairdii (7); Oncorhynchus mykiss (4); Oncorhynchus nerka (4); Osmerus mordax (12); Pleuronectidae gen. sp. (9); Pollachius virens (9); Prosopium williamsoni (4); Ptychocheilus oregonensis (4); Salvelinus fontinalis (2, 13); Salvelinus malma (4); Scomber scombrus (9); Sebastes sp. (9); Synaphobranchus kaupii (7)

Distribution: Atlantic, British Columbia, Labrador, New Brunswick, Nunavut, Ontario, Quebec

Records: 1. Szuks 1980 (AT); 2. G. A. Black 1981a (QC); 3. Appy & Burt 1982 (AT); 4. Anon. 1984 (BC); 5. Pálsson & Beverley-Burton 1984 (AT); 6. Bradstreet et al. 1986 (NU); 7. Houston & Haedrich 1986 (AT); 8. Landry et al. 1986 (NB); 9. Morrison et al. 1986 (AT); 10. Dechtiar & Christie 1988 (ON); 11. Dechtiar et al. 1988 (ON); 12. Landry & Hare 1990 (AT); 13. Marcogliese & Cone (LB); 14. Landry et al. 1992 (AT)