Three new species of Pseudohaliotrema Yamaguti, 1953 (Monogenea: Ancyrocephalidae) from Siganus species (Siganidae) and the description of a mechanism for cross-insemination

Three new species of Pseudohaliotrema Yamaguti, 1953 were collected from two Siganus species caught off Singapore. They are Pseudohaliotrema virgata n. sp. and P. molnari n. sp. from Siganus virgatus and P. falcata n. sp. from S. guttatus. They differ in the shape and size of both the body and haptoral sclerites and in the morphology of the male organ (modified copulatory organ). Pseudohaliotrema species from siganids are characterized by having a large prominent vaginal pouch, an eversible spermatophore transfer tube associated with the vaginal pouch, ovoid spermatophores (in mature worms), a male organ adapted for spermatophore formation, a large prostatic reservoir, and a testis and ovary arranged side by side. Pseudohaliotrema plectocirra Paperna, 1972 is re-assigned as Tetrancistrum plectocirra (Paperna, 1972) n. comb. Pseudohaliotrema species from non-siganid fish do not possess these characteristics and belong elsewhere. The generic diagnosis of Pseudohaliotrema is amended. Pseudohaliotrema species use a spermatophore for sperm transfer, which is documented in detail for P. virgata n. sp. The same reproductive strategy is used by P. molnari n. sp. and P. falcata n. sp., as indicated by the presence of spermatophores on the spermatophore transfer tube and inside the vaginal pouch. The presence of individuals exchanging spermatophores indicates that P. sphincteroporus Yamaguti, 1953 and P. sigani Yamaguti, 1953 also employ the same mechanism. The spermatophore, assembled in the sclerotized male organ and stored in the spermatophore chamber, is retrieved by the eversible spermatophore transfer tube (housed within the vaginal pouch) and drawn into the vaginal pouch as the spermatophore transfer tube invaginates. Within the vaginal pouch, the wall of the spermatophore disintegrates releasing spermatozoa.