We describe Parorchis laffertyi n. sp., a trematode infecting the California horn snail, Cerithideopsis californica (Haldeman, 1840), as a first intermediate host. The first intermediate host stages of this species were previously cryptic with Parorchis catoptrophori Dronen we also document a metacercaria developmental time series. We experimentally exposed final host chickens (Gallus gallus domesticus Linnaeus, 1758) and ducks (Anas platyrhynchos domesticus Linnaeus, 1758) to metacercariae per cloaca and successfully obtained and described the sexual adults of P. catoptrophori and an immature adult of P. laffertyi from the chickens. Both cytochrome c oxidase subunit I (COI) and 28S rDNA phylogenetic analyses supported the hypothesis that P. catoptrophori and P. laffertyi are 2 species of Parorchis Nicoll, 1907. As indicated in its original description, adults of P. catoptrophori can be readily distinguished from adults of other Parorchis species by their possession of a greater number of collar spines (∼80 vs. ∼60 in most other species); a bipartite pharynx; a pharynx to oral sucker ratio of ∼1:2; presence of esophageal diverticula; and deeply lobed testes. The immature adult of P. laffertyi can be distinguished from adults of other Parorchis species by the collar spine number (∼55); bipartite pharynx; a pharynx to oral sucker ratio of ∼1:2; presence of esophageal diverticula; and distinct COI and 28S sequence data. Mature adult specimens of P. laffertyi are needed to parse additional morphological characteristics. We used our morphometric data and additional published information to provide an emended diagnosis for the genus Parorchis. There are now 18 formally named Parorchis species, 4 of which have had their first intermediate host stages described and 4 of which have available DNA sequence information.
Nelson et al. (Mon,) studied this question.