Its asexual stage resides in the body of whelks where it replicates many times, and eventually its eggs are dispersed in the water through feces.

The asexual life cycle of C. longicollis is complex which involves carnivorous scavenging whelks, a variety of fish, and gulls.

The asexual stages of C. longicollis reside in the body of whelks where it replicates many times, producing a stream of swimming larvae call cercariae.

The final host for this parasite are gulls, when they eat the fluke that reside in parasitised fish.

This pile of parasite-laden fish present opportunistic gulls with a rich and accessible feast.