Ariolimax columbianus, an Intermediate Host for Brachylaemus virginiana (Dickerson) (Trematoda: Digenea) in California

Abstract

On March 3, 1951 a young male opossum was captured in Tilden Park, Contra Costa Co., California. The animal had a droopy, sickly appearance and was killed and examined for parasites. Several hundred small flukes, later identified as Brachylaemus virginiana (Dickerson), were found in the small intestine. Several months previously one of us had found metacercariae in the kidney of Ariolimax columbianus. This slug is commonly found in the Pacific Coast region and is restricted to this area. Comparison of the metacercariae with the flukes obtained from the opossum, as well as examination of pertinent literature (Dickerson 1930, Krull 1935), indicated clearly that the larvae from the slugs were metacercariae of Brachylaemus virginiana. Of 97 Ariolimax columbianus collected on the Mills College Campus, Alameda Co., California, 94 harbored this metacercaria in the kidneys. There were approximately two dozen larvae per kidney, while specimens with as few as one or two and others with as many as 50 or more were observed. In addition, 6 out of 8 Ariolimax columbianus from Berkeley, Alameda Co., California were infected. Seven A. californicus brachycephalus from San Mateo Co., California were found to be negative. Although the digestive, hermaphroditic and albumen glands were examined in several specimens of A. columbianus, no sporocysts or cercariae were found. Krull (1936) listed 1 slug and 5 snail intermediate hosts for Brachylaemus virginiana. We therefore examined a number of common gastropods, in order to determine possible additional hosts for the larval stages of this fluke. Of 20 Milax gagates, 10 Limax marginatus, 1 Limax flavus, 20 Deroceras reticulatum and 6 Helminthoglypta arrosa holderiana not a single one was infected. All these gastropods were collected on the Mills College Campus between February and May 1951 in the same habitat with Ariolimax. Three Helminthoglypta nickliniana from Tilden Park, Contra Costa Co., California, were also negative. Since the slug Deroceras laeve is a host for the metacercaria (Krull, 1936) one would expect that D. reticulatum might also be suitable. This was not so, however, and it was somewhat surprising to find the metacercariae only in Ariolimax. It may be that the food habits of the above mentioned gastropods are in part responsible for this situation. Ariolimax columbianus has been observed to congregate around and feed on feces in nature. None of the other species listed has been observed to do so. In relation to the opossum in California, we should like to stress that this animal was introduced into the state, the earliest record being sometime after 1880 (Grinnell, Dixon and Linsdale, 1937); subsequently it was introduced repeatedly around