The status of Petalocotyle Ozaki, 1934 (Digenea : Gyliauchenidae), including the description of two new species from acanthurid fishes in Queensland,Australia

The status of Petalocotyle Ozaki, 1934 within the Gyliauchenidae Goto & Mat sudaira, 1918 is reviewed. Two new species, P. adenometra from Prionurus mi crolepidotus (Amity Point, Queensland, Australia) and P. diverticulata from Acanthurus nigrofuscus and A. lineatus (Heron Island, Queensland, Australi a), are described. The body plan of Petalocotyle conforms to that of member s of the Gyliauchenidae (oral sucker absent, well-developed pharynx, comple x oesophagus and characteristic male terminal genitalia), indicating justif iable inclusion in this family. A new diagnosis is given for the genus, suc h that Petalocotyle is now identified by the presence of an anterior, protu berant ventral sucker, long caeca, a large, sigmoid cirrus-sac containing a coiled ejaculatory duct, and an extensive vitellarium. We suggest that, of all the known genera of gyliauchenids, Petalocotyle may most closely resem ble the 'archaetypal gyliauchenid', that is, it may be placed basally withi n the radiation of the Gyliauchenidae. However, derived characters, like di verticula in the reproductive system, indicate that some characters of indi vidual members of Petalocotyle may be considered advanced and do not reflec t an archaetypal condition. Parallels in the structure of the male and fema le genitalia of Robphildollfusium Paggi & Orecchia, 1963 and Petalocotyle, along with the shared morphology of the digestive tract, indicate possible phylogenetic links between the two genera. This affinity is difficult to in fer using morphology alone and recommend that Robphildollfusium remain deta ched from the Gyliauchenidae.