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Studies on Gyrocotyle rugosa Diesing, 1850, A Cestodarian Parasite of the Elephant Fish, Callorhynchus milii



Gyrocotyle is a genus of cestodarian flatworm occurring in the spiral valve of chimaeroid fishes. Due to the large size of the adult worms they have been known for many years. A review of the genus by Dollfus (1923) has a bibliography of 75 papers. In this literature a surprising amount of controversy developed regarding which end of the parasite was anterior. The study of numerous postlarval stages by Lynch (1945) seems to prove definitely that the characteristic, ruffled "rosette" is posterior. The history of the genus will not be repeated here since it is well summarized by Watson (1911), Dollfus (1923). and Lynch (1945).

Three species of Gyrocotyle are now recognized: Gyrocotyle rugosa Diesing, 1850 (the type species); G. urna (Grube and Wagener, 1852); and G. fimbriate Watson,. 1911. Of these specks G. rugosa is least well known. Spencer's (1889) description of this species from the elephant fish is unreliable since he compiled it from specimens of both G. rugosa and G. urna. The purpose of this paper is to present certain additions to the description of the adult worm: describe the lycophore larva, some postlarval stages, and a few experiments with these larvae. Most of the study was made at Victoria University College, Wellington, but some of the experimental work with larvae was done at the Portobello Marine Station near Dunedin.

Gyrocotyle rugosa is a common parasite in the spiral valve of the elephant fish, Callorhynchus milii Bory (= C. antarcticus Lacépède) in New Zealand waters. Of 16 hosts examined all except three were infected with Gyrocotyle species, page 2 usually G. rugosa. The uninfected fish had been dead some hours and in one case two Gyrocotyle were found in the container near the fish. It is well known that upon death of the host these parasites often migrate to the exterior either by way of the anus or mouth. Thus, the actual incidence of infection in New Zealand must be very high.

Gyrocotyle urna also occurs in Callorhynchus in New Zealand but is much less common. It, but not G. rugosa, occurred in two of the 16 hosts examined. Three specimens occurred in one host, two in the other. Only one specimen was stained and cleared. These specimens agreed with G. urna and differed from G. rugosa in several easily recognized characters, viz.: the lateral frills or undulations of the body; the presence of body spines; the eggs containing undeveloped embryos; and the small extent of the lateral coils of the uterus. The lateral extent of the uterus was 14 to 22 per cent. of greatest body width (in three specimens). The extent of body undulations and relative width of the rosette were like that described for G. urna rather than fimbriata. The extent of the left testicular field in a 50 mm. specimen was 6 mm. or 12 per cent. of the body length, as in G. urna. Vitellaria were not observed posterior to the dorsal pore but their exact posterior boundary was not clear. In a few respects, however, my material does not agree with G. urna. The number of acetabular spines was 50 to 60 on each side, rather than 17 to 25, a number more like that of G. fimbriata. The largest acetabular spine was only 0.214 mm. or 7.7 per cent. of acetabular length and smaller than the largest body spines. Thus, both number and size of these spines agree better with G. fimbriata. The size, however, is nearly that of G. urna forma parvispinosa. The male pore was rather far to the right nearer the edge of the body than to the midline. Excretory pores could not be seen. While study of more specimens might possibly indicate a new species for this material it is considered for the present to be G. urna.