On the endoparasites ofBuccinum undatumL. with special reference to the trematodes

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Abstract
In all 1375 Buccinum undatum from the Sound (Øresund) were collected during a one year period (May 1966–April 1967), and 325 Buccinum from the Gullmarfjord, Sweden, August 1967. Four species of larval trematodes were found in Buccinum from Øresund: Cercaria Neophasis lageniformis, C. Zoogonoides viviparus, C. buccini and a xiphidiocercaria of the genus Renicola, all in the digestive gland and in the gonad. An adult trematode, Steringophorus furciger, which occurs in the stomach, does not produce mature eggs in Buccinum, but attains the same size as in the true final hosts, various flatfishes. The vertebrate hosts of this trematode and Buccinum feed on the same diet, and Buccinum becomes, therefore, presumably infected by ingesting metacercariae with the food. The two last-mentioned trematodes have not previously been found in Buccinum. A turbellarian, Graffilla buccinicola, and two sporozoans, Merocystis kathae and Piridium sociabile, were also found. In eight cases two different species of cercariae were present in the same Buccinum. Chisquare tests showed that the different species of trematodes did not affect the presence of each other in Buccinum. Male and female whelks had the same infection percentages and there was no great variation in the level of infection during the course of the year. All infections with larval trematodes resulted in castration of the host. The penis of infected males was generally smaller than that of uninfected whelks, and large Buccinum with a small penis always proved to be infected. The small size of the penis was largely or entirely due to reduction, not to arrest of the growth at the moment of infection.