Zoogonus lasius* is a digenean trematode whose first host is the Eastern Mudsnail (Ilyanassa obsoleta). The cercariae (swimming larvae) develop in the snail and then are released into the water where they penetrate the polychaete Alitta (=Nereis) virens, where they encyst in the parapodia. When the host worm is eaten by various species of fishes, the trematodes develop into their adult stage. On the East Coast, adult parasites developed in the Oyster Toadfish Opsanus tau, the American Eel (Anguilla rostrata, Menidia menidia, Leiostomus xanthurus, and Trinectes maculatus. On the West Coast, the parasites are likely to infect a range of fish hosts.
* This species was first reported as Z. rubellus, by Blakeslee et al. 2012. That species is native to the Northeast Atlantic, and a parasite of Tritia reticulata (Netted Dog Whelk). The two trematodes have been treated as conspecific, but differ in size and morphology.