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

Gyrocotyle rugosa. Adults (Figs. 1, 2)

Gyrocotyle rugosa. Adults (Figs. 1, 2)

Body size and proportions vary considerably with contraction. The worms are strongly muscular and it is difficult to preserve them in their normal shape. Living specimens are soft and flabby, creamy-white in colour. Watson (1911) noted that in freshly killed hosts the worms were a pinkish, translucent flesh colour. Measurements of 22 specimens were: length 32 to 82 mm., greatest width 6.5 to 22 mm. A dead specimen, greatly extended, was 130 by 15 mm. Moderately contracted worms were 42 to 71 by 16 to 20 mm. Lateral undulations of the body are lacking. The lateral edges tend to curve slightly inward ventrally but the striking undulations present in other species do not occur. The rosette is highly frilled, fully as much so as in G. urna although usually less than is true for G. fimbriata. The diameter of the rosette is 33.1/3 to 50 per cent. of greatest body width, thus resembling G. urna.

The body surface is rugose even in extended or compressed specimens. The rugae are transverse except in the anterior half of the body ventrally where short longitudinal folds occur irregularly so that the surface is incompletely broken into irregular segments. Body spines such as occur in G. urna and G. fimbriata are lacking, but numerous exceedingly minute spines or points occur on the tips of small papilla-like elevations (Fig. 2). These papillae and spines are best observed by reflected light when the body surface is exposed to the air. They are invisible in cleared specimens. They are arranged more or less in transverse rows on the page 3 body ridges. Where the rugae or ridges are irregular the spines are also irregular. They occur on both the dorsal and ventral surfaces and on the rosette but appear to be lacking anterior to the vaginal pore.

The acetabular spines occupy a subtriangular area on each side opposite the posterior half of the acetabulum. In two specimens, the length of the spiny area was 71 per cent. and 74 per cent. of the acetabular length. The spines are lateral and ventral and perpendicular to the body surface. The area is longest on the edge of the body and tapers as it extends ventrally almost to the acetabulum. The largest spines are 0.357 by 0.065 mm. or 13 per cent. of the length of the acetabulum. The number of spines, estimated to he approximately 100 on each side, is greater than in either G. urna or G. fimbriata.

The genital notch is conspicuous on the right side of the body a little posterior to the acetabulum. The uterine pore is median about 1/6th body length from the anterior end. The male pore is at the tip of a pointed, cone-like elevation of the body surface, the genital papilla or genital cone. Fresh, living specimens may show this structure only slightly elevated, but after a few minutes outside the host and during killing and fixation it extends toward the right, usually to and even through the genital notch. Here it bends dorsally and may almost reach the vaginal pore. As has been noted by previous authors, it evidently can serve in self-copulation. It appears not to be a true cirrus or any specialized structure but merely an elevation of the body wall. When the cone is retracted, the male pore lies just median to the right longitudinal nerve and only slightly posterior to the genital notch. The vaginal pore is dorsal, well to the right of the longitudinal nerve, and near the genital notch. Excretory pores were not observed but the excretory tubes were seen to approach the edges of the body 14 mm. from the anterior end of a specimen the acetabulum of which was 2.5 mm. long. This distance of more than five times acetabular length is considerably more posterior than in the other species. In another specimen 44 mm. long and with acetabulum 2.2 mm. long, a diagonal excretory tube extended to each side of the body 16 mm. from the anterior end.

Testes are numerous, estimated 400 to 500 on each side, and close together. They extend anteriorly to near the base of the acetabulum and posteriorly well beyond the uterine sac, to about the tenth lateral coil of the uterus. Approximately half the longitudinal extent of the testes is posterior to the uterine sac. In a 32 mm. specimen with acetabulum 1.90 mm, long, the testicular field was 10 mm. or 31 per cent. of body length and more than five times acetabular length.

The ovary is approximately 26 per cent. of body length from the posterior end. The lateral coils of the uterus are much longer and much snore numerous than in other species. In 22 specimens measured, the width of the uterus was 40 to 81 per cent. of greatest body width. In only one specimen was it less than 50 per cent. and the average was 60 per cent. Since the gravid uterus is visible from the surface, this character alone easily distinguishes G. rugosa from G. urna and G. fimbriata which have short uterine coils. The vitelline follicles extend from about mid-acetabular level to a short distance posterior to the ovary. They are not limited to the lateral fields but extend across the body both ventral and dorsal to the acetabulum, the testes, and most of the uterus. Medianly they tend to be more sparse and are few or lacking opposite the ovary and the terminal eight or ten coils of the uterus. The distance between the posterior limit of the vitellaria and the posterior end of the body was 7.8 mm. in a 70 mm. specimen, and 7 mm. in a 40 mm. specimen, a greater distance than occurs in the other two species.