Pharurus pallasii (Van Beneden, 1870) Arnold & Gaskin, 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 : 176-177

* Pharurus pallasii (Van Beneden, 1870) Arnold & Gaskin, 1975

Preamble: Pharurus pallasii matures in the cranial sinuses, middle ears, and Eustachian tubes of beluga whales ( Delphinapterus leucas ) in Canadian and other waters. Some 1st -stage larvae of P. pallasii intubated by Houde et al. (2003) into the stomach of Canadian-caught American plaice ( Hippoglossoides platessoides ) and Arctic sculpins ( Myoxocephalus scorpioides ) moulted to 2nd stage in the intestinal wall of both fish species. A description of 1st - and 2nd -stage larvae of P. pallasii is provided here although evidence that fishes serve as intermediate hosts of the species in Canadian waters appears to be lacking.

First-stage larvae (measurements in µm): 295±21 long, 15±1 wide ( Fig. 102 A). Oesophagus 134±8 long. Nerve ring 62±5, excretory pore 66±7, and genital primordium 176±7 from anterior end. Tail 37±7 long, delicate, ending in sharp point.

Second-stage larvae (measurements in µm): 364±21.3 long, 12 ±1 wide, 2nd -stage larvae retain cuticle of the 1st stage ( Fig. 102 B). Oesophagus 166±30 long. Nerve ring 64±6, excretory pore 69±5, and genital primordium 212±34 from anterior end. Tail 33±7 long, resembles that of the 1st stage.

Site: intestinal wall

Hosts: Hippoglossoides platessoides (EX); Myoxocephalus scorpioides (EX) Distribution: Quebec

Record: Houde, Measures & Huot 2003

Figures

FIGURE 102. * Pharurus pallasii (Van Beneden, 1870) Arnold & Gaskin, 1975. A. 1 st - stage larva, lateral view; B. 2 nd - stage larva within loose cuticle of 1 st - stage larva, lateral view. (Redrawn from Houde et al. 2003)