Hysterothylacium incurvum (Rudolphi, 1819) 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 : 143-144

Hysterothylacium incurvum (Rudolphi, 1819) Deardorff & Overstreet, 1981

Synonyms: Thynnascaris incurva (Rudolphi, 1819) Dollfus, 1935 ; Contracaecum incurvum (Rudolphi, 1819) Baylis & Daubney, 1922

Description (after Deardorff & Overstreet 1981). With characteristics of the genus. Body reaching greatest width near midbody. Cuticle with inconspicuous annulations except ventrally on male’s posterior. Lateral alae bifurcate at their tips throughout worm. Cervical alae not flaring. Lips approximately equal in size, all wider than long; flanges widest near base, indented at anterior 1/3. Pulp conspicuously narrow near base. Interlabia with height two times greater than width at base, with rounded tips. Interlabial grooves deep, adjacent grooves nearly merging at base of each lip ( Fig. 82 A). Preventriculus clavate, 7–16% of body length. Ventriculus narrower than widest level of preventriculus. Nerve ring located between anterior 7–19% of preventriculus. Excretory pore immediately posterior to nerve ring level. Tail gradually tapering, usually without spines.

Males: body 17–34 long by 0.606–0.772 wide. Preventriculus 2.3–5.2, ventriculus 0.117–0.166, ventricular appendix 1.7–2.6, and intestinal caecum 1.9–4.5 long. Spicules 2.6–8.7 long, equal in eight specimens, left one longer in two specimens: spicule ratio 1:0.9–1.0, Caudal papillae 31 to 32 pairs: 27 to 28 pre-cloacal pairs, four post-cloacal pairs, one para-anal papilla, doubled. Distinct medioventral pre-cloacal organ, papillated. Modified annules on ventral surface, beginning near anus, extending anteriorly 2.0–6.1 ( Fig. 82 B). Tail flexed ventrad, without spines.

Females: body 25–69 long by 0.5–1.7 wide. Preventriculus 2.6–7.2, ventriculus 0.173–0.362, ventricular appendix 0.6–4.0, and intestinal caecum 1.5–5.1 long. Vulva opening 7.3–35.1 from anterior end. Ovaries rarely extending anteriad to vulva level. Eggs 0.018–0.063 in diameter. Tail usually without spines. Site: stomach

Host: Xiphias gladius

Distribution: Atlantic

Records: Nigrelli 1938; Tibbo et al. 1961; Iles 1971; Hogans et al. 1983

Figures

FIGURE 82. Hysterothylacium incurvum (Rudolphi, 1809) Deardorff & Overstreet, 1981. A. head, lips, dorsal view, showing interlabial groove (ig); B. male, posterior end, showing caudal papillae and annules on ventral surface, lateral view. (Redrawn from Deardorff & Overstreet 1981)