Hysterothylacium aduncum (Rudolphi, 1802) Deardorff & Overstreet, 1981

Arai, Hisao P. & Smith, John W., 2016, Guide to the Parasites of Fishes of Canada Part V: Nematoda, Zootaxa 4185 (1), pp. 1-274 : 139-141

** Hysterothylacium aduncum (Rudolphi, 1802) Deardorff & Overstreet, 1981

Synonyms: Thynnascaris adunca (Rudolphi, 1802) Hartwich, 1957 ; Contracaecum aduncum (Rudolphi, 1802) Baylis, 1920 ; Contracaecum gadi (O. F. Müller, 1777) Johnston & Mawson, 1945 ; Contracaecum clavatum (Rudolphi, 1809) Baylis, 1920

Description (after Moravec 2013). With characteristics of the genus. Females larger than males. Lips of approximately equal size, with wide membranous flanges broadest near their base; dorsal lip with two subdorsal papillae; each subventral lip with one double subventral papilla and small simple papilla and amphid situated laterally; pulp of lips with at either side small rounded lobe at its anterior margin. Interlabia triangular, broad, with distinct cuticular margin. Interlabial grooves absent. Cervical alae starting short distance below level of base of subventral lips, gradually becoming wider (maximum width 0.04–0.05) and extending posteriorly to posterior limit of preventriculus. Preventriculus narrow, small ventriculus globular; ventricular appendix narrow, about as long as intestinal caecum; intestinal caecum represents about 30–40% of preventricular length. Nerve ring encircling preventriculus at border of first and second fifths of its length; excretory pore just below nerve ring level. Intestine dark, straight. Rectum short, hyaline, surrounded by three unicellular rectal glands. Tail of both sexes conical, ending in small process covered with fine spines.

Males: 18.0–35.0 long, maximum width 0.430–0.800. Dorsal lip 0.151–0.153 long, 0.144 wide; ventro-lateral lips 0.138–0.150 long, 0.131–0.138 wide ( Fig. 80 A). Preventriculus 1.94–3.23 long, ventriculus 0.154–0.170 x 0.124–0.144, ventricular appendix 0.54–0.64 long, and intestinal caecum 0.65–0.93 long. Nerve ring and deirids 0.530–0.540 and 0.590–0.600 from anterior end. Tail conical, 0.108–0.139 long, ending in small process covered with fine spines ( Fig. 80 D). Twenty three pairs pre-cloacal papillae, two pairs ad-cloacal papillae, and four to five pairs post-cloacal papillae—last pair lateral, remaining pairs subventral. Anterior cloacal lip with one unpaired papilla. Spicules equal, 2.00–4.65 long, with narrow membranous wings; distal tip of spicules rounded ( Fig. 80 C).

Females: 24.0–48.0 long, maximum width 0.72–1.40. Dorsal lip 0.143–0.155 long, 0.149–0.181 wide; ventrolateral lips 0.153 long, 0.159–0.163 wide. Preventriculus 2.25–4.12 long, ventriculus 0.171–0.180 x 0.155–0.165, ventricular appendix 0.62–0.69 long, and intestinal caecum 0.91–1.08 long. Nerve ring and deirids 0.66–0.90 and 1.08 from anterior end ( Fig. 80 B). Tail conical 0.270–0.420 long, ending in small process covered with fine spines. Vulva at end of first third of body length, 9.0–16.5 from anterior end. Vagina narrow, long, directed posteriorly and dividing into two posteriorly directed uterine branches filled with eggs; ovaries situated in posterior part of body. Eggs almost spherical, 0.062–0.070 x 0.046–0.047.

L4: 12.0–31.0 long, maximum width 0.22–0.47. Mouth surrounded by three lips comparatively narrow, lacking the large flanges of adults. Preventriculus 1.85–3.85 long, ventricular appendix 0.61–0.98, intestinal caecum 0.65–1.23. Nerve ring and excretory pore 0.34–0.61 and 0.42–0.66 from anterior end. Tail conical, 0.11– 0.29 long, tail tip covered with numerous minute projections.

L3: 6.6–21.6 long, maximum width 0.16–0.33. Mouth opening usually T-shaped, two basal projections of ventral boring tooth extending along its margin. No distinct lips present. Two subventral and two subdorsal papillae at anterior end as well as one dorsal antero-median papilla. Cuticle transversely striated. Preventriculus 1.00–2.00 long, ventriculus small. Ventricular appendix 0.40–0.68 long, intestinal caecum 0.33–0.92 long. Nerve ring and excretory pore 0.28–0.45 and 0.31–0.50 from anterior end. Tail conical, 0.12–0.21 long, with pointed tip.

Comments: Hysterothylacium aduncum appears to be the most abundant species of the genus known from marine fishes in Canadian waters. According to Klimpel & Ruckert (2005) it is also the most abundant anisakid nematode of North Sea fishes. Hysterothylacium aduncum may be carried into Canadian fresh waters by anadromous or catadromous fishes but is not able to reproduce there.

Sites: alimentary tract, body cavity, intestinal lumen, mesenteries, musculature, stomach, stomach wall, viscera Hosts: Alosa pseudoharengus (13); Alosa sapidissima (28, 58); Ammodytes dubius (10); Anarhichas lupus (47);

Atheresthes stomias (36, 66); Aulorhynchus flavidus (5); Clupea harengus (38, 40, 44); Clupea pallasi (16, 17,

18, 19); Coryphaenoides rupestris (11, 12, 23, 24, 43); Cryptacanthodes giganteus (3); Eopsetta jordani (2, 3);

Gadus macrocephalus (3); Gadus morhua (1, 13, 14, 25, 29, 53, 68, 72, 73); Glyptocephalus cynoglossus (4,

21, 29); Glyptocephalus zachirus (2, 3); Hippoglossoides elassodon (2, 3); Hippoglossoides platessoides (4,

21, 29, 42, 61); Hippoglossus hippoglossus (4, 21); Hippoglossus stenolepis (62, 65); Hypomesus pretiosus

(3); Limanda ferrugineus (4, 61); Macrourus berglax (23); Mallotus villosus (46, 60); Melanogrammus

aeglefinus (13, 14, 22); Merluccius albidus (50); Merluccius bilinearis (50); Merluccius productus (30);

Microgadus tomcod (1); Microstomus pacificus (36); Myoxocephalus scorpius (1); Nezumia bairdii (23);

Oncorhynchus gorbuscha (27, 32); Oncorhynchus keta (32, 41); Oncorhynchus kisutch (3, 32); Oncorhynchus

mykiss (37); Oncorhynchus nerka (3, 32); Ophiodon elongatus (3); Parophrys vetulus (2, 3, 36); Phycis

chesteri (50); Podothecus accipenserinus (5); Pseudopleuronectes americanus (1, 4, 61, 67, 70); Reinhardtius

hippoglossoides (21, 51, 55, 56, 57, 59, 64); Rhinochimaera atlantica (35); Salmo salar (1, 6, 7, 9, 20); Salvelinus alpinus (9, 31, 39, 52); Salvelinus fontinalis (45, 48, 49); Salvelinus namaycush (9, 31); Scomber scombrus (1, 13); Sebastes aleutianus (15); Sebastes alutus (3, 15); Sebastes babcocki (15); Sebastes brevispinis (15); Sebastes caurinus (15); Sebastes crameri (15); Sebastes diploproa (15); Sebastes entomelas (15); Sebastes fasciatus (34, 63); Sebastes flavidus (15); Sebastes helvomaculatus (15); Sebastes maliger (15); Sebastes mentella (34, 63, 69); Sebastes nebulosus (15, 54); Sebastes norvegicus (34); Sebastes paucispinis (15); Sebastes pinniger (15); Sebastes polyspinis (15); Sebastes proriger (15); Sebastes reedi (15); Sebastes ruberrimus (3, 15); Sebastes variegatus (15); Sebastes zacentrus (15); Tautogolabrus adspersus (1); Theragra chalcogramma (3, 26, 33, 36); Urophycis chuss (50); Urophycis tenuis (50, 71); Xiphias gladius (28)

Distribution: Atlantic, British Columbia, Labrador, New Bruswick, Newfoundland, Nova Scotia, Northwest Territories, Pacific

Records: 1. Heller 1949 (AT); 2. Margolis 1952a (PA); 3. Margolis 1952b (PA); 4. Ronald 1963 (AT); 5. Arai 1969 (PA); 6. Pippy 1969 (AT, NS); 7. Pippy 1970 (AT); 8. Sekhar S. [sic] & Threlfall 1970 (AT); 9. Hicks & Threlfall 1973 (LB); 10. Scott 1973 (AT); 11. Zubchenko 1975 (AT); 12. Zubchenko 1976 (AT); 13. Gaevskaya & Umnova 1977 (AT); 14. Linkletter et al. 1977 (AT); 15. Sekerak & Arai 1977 (PA); 16. Arthur 1978 (PA); 17. Arthur & Arai 1979 (PA); 18. Arthur & Arai 1980a (PA); 19. Arthur & Arai 1980b (PA); 20. Pippy 1980 (AT); 21. Zubchenko 1980 (AT); 22. Scott 1981 (AT); 23. Zubchenko 1981a (AT); 24. Zubchenko 1981b (AT); 25. Appy & Burt 1982 (AT); 26. Arthur et al. 1982 (PA); 27. Margolis 1982 (NF); 28. Hogans et al. 1983 (AT); 29. McClelland et al. 1983a (AT); 30. Sankurathri et al. (PA); 31. Stewart & Bernier 1983 (NT); 32. Anon. 1984 (BC); 33. Arthur 1984 (PA); 34. Bourgeois & Ni 1984 (AT); 35. Hogans & Hurlbut (AT); 36. Kabata & Whitaker 1984 (PA); 37. Margolis 1984 (PA); 38. McGladdery 1984 (AT); 39. Stewart & Bernier 1984 (NT); 40. McGladdery & Burt 1985 (AT); 41. Whitaker 1985 (PA); 42. Zubchenko 1985a (AT); 43. Zubchenko 1985b (AT); 44. Chenoweth et al. 1986 (AT); 45. Frimeth 1986 (NB); 46. Pálsson 1986 (AT); 47. Bray 1987 (AT); 48. Frimeth 1987a (NB); 49. Frimeth 1987b (NB); 50. Scott 1987 (AT); 51. Wierzbicka 1988 (AT); 52. Bouillon & Dempson 1989 (LB); 53. Brattey et al. 1990 (AT); 54. Holmes 1990 (PA); 55. Wierzbicka 1991a (AT); 56. Wierzbicka 1991b (AT); 57. Krzykawski & Wierzbicka 1992 (AT); 58. Hogans et al. 1993 (AT); 59. Arthur & Albert 1994 (AT); 60. Arthur et al. 1995 (AT); 61. Martell & McClelland 1995 (AT); 62. Blaycock 1996 (PA); 63. Moran et al. 1996 (AT); 64. Boje et al. 1997 (AT); 65. Blaycock et al. 1998a (PA); 66. Wierzbicka & Piasecki 1998 (PA); 67. Khan 1999 (AT); 68. Lee & Khan 2000 (AT); 69. Marcogliese et al. 2003 (AT); 70. McClelland et al. 2005 (AT); 71. Melendy et al. 2005 (AT); 71. Khan et al. 2011 (NF); 73. McClelland & Melendy 2011 (AT)

Figures

FIGURE 80. ** Hysterothylacium aduncum (Rudolphi, 1802) Deardorff & Overstreet, 1981. A. male, head; B. female, anterior end; C. male, posterior end; D. male, tail tip showing spiny process. (Redrawn from Moravec 2013)