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

Postlarval Stages of G. rugosa. (Figs. 9, 10)

Postlarval Stages of G. rugosa. (Figs. 9, 10)

It was discovered more or less accidentally that numerous very small postlarval stages of G. rugosa occurred in the mucus of the anterior portions of the spiral valve of infected fishes. By scraping the wall of this organ with a scalpel living specimens can easily be found. They all possess a posterior, conspicuous, expanded, circular or subcircular, haptor-like organ bearing the larval hooks. The smallest specimens had a body length, not including the haptor, only slightly more than the length of the ciliated lycophore. AH were non-ciliated. The total body length, including the haptor, and the greatest width varied from 0.225 by 0.098 mm. to 0.957 by 0.280 mm. The body is uniformly filled with nuclei and shows less differentiation of cellular groups than does the ciliated lycophore. A depression is visible at the anterior end, and in the larger specimens a concentration of nuclei indistinctly outlines the rudiments of the acetabulum. In the 0.943 mm. specimen the acetabulum was 0.143 by 0.072 mm. The haptor contains more scattered nuclei. It was 0.108 mm. in diameter in a 0.686 mm. specimen. The hooks retain their original size but become more widely separated in the larger specimens. No evidence of the overgrowth of the haptor by the body as noted by Lynch for G. fimbriata was seen.

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Similar postlarval stages have been described embedded in the tissues of adult specimens of G. urna, G. fimbriata, and G. rugosa. None such were observed in the few specimens stained and cleared. In view of the common occurrence of these larvae in the spiral valve of the host, it seems probable that their penetration into an adult Gyrocotyle is accidental.

Fuhrmann (1930), commenting on the occurrence of young larvae in the tissues of adult specimens, stated; "Die 10-hakigen Larven bohren sich vielleicht normalerweise in die Mucosa des Darmes ein (anomalerweise ins Parenchym des Gyrocotyle), um sich dort zu entwickeln und dann wieder in den Darm zu gelangen, wo sie geschlechtsreif werden." He gave no evidence to support this possibility which he apparently proposed as a theory. It is supported by the above findings of numerous very young larvae in the mucosa. It will be shown below that there is a possibility that these larvae may have reached the mucosa by way of the blood stream rather than by way of the digestive tract.