Abstract
Trematodes of the genus Philophthalmus are cosmopolitan parasites that infect the eyes of birds and mammals. They have the potential to affect the survival of their hosts and a few cases of human philophthalmiasis have occurred worldwide. Adults of known Philophthalmus species have never been recorded from bird hosts in New Zealand, despite their cercarial stage being a focus of various studies. Here, we describe a new species of Philophthalmus infecting New Zealand red-billed and black-backed gulls, Philophthalmus attenuatus n. sp. It is distinguished from other marine species of Philophthalmus by its long, thin body shape, consistently longer vitelline field on the left, and its body reflexed at the ventral sucker. We use molecular methods to complete the life cycle of this species, matching it with the larval stage infecting the mud whelk, Zeacumantus subcarinatus, and present a preliminary cox1 phylogeny. In addition, we comment on the validity of some taxonomic characters used to differentiate species of this genus, discuss potential colonisation routes to New Zealand and comment on the potential for zoonotic infection.