Description of Paraschistorchis australiensis n. sp. (Digenea: Megaperidae) as a distinct species from Paraschistorchis seychellesiensis (Toman, 1989).

Abstract

Differences in testes arrangement and length of post-testicular region between Australian specimens of Paraschistorchis seychellesiensis sensu Magro, Cutmore, Carrasson & Cribb, 2023 and the original description of Paraschistorchis seychellesiensis (Toman, 1989) Blend, Karar & Dronen, 2017 from the Indian Ocean have raised a question whether such variations are intraspecific or interspecific variations. To address this, in-depth morphological descriptions and species delimitation analyses were conducted using a combination of comparative morphology, multivariate classification analyses, and host-parasite data. The Australian population of P. seychellesiensis differs from all known species of Paraschistorchis Blend, Karar & Dronen, 2017 by a broad linguiform body, a ventral sucker noticeably smaller than the oral sucker, a subquadrate pharynx that is partly dorsal to the oral sucker, and testes arrangement in a cluster configuration, as well as its distinct spatial clustering within all multivariate classification analyses without any intrusion into the space occupied by another cluster. Furthermore, the distinctive extension of the anterior vitellarium, significant differences in anterior testis/ovary ratios, and egg sizes indicate that Australian and Indian specimens of P. seychellesiensis are two distinct species. The apparent comparatively distant geographic localities, each with distinct ecosystems (Seychelles Islands vs Great Barrier Reef [GBR], Australia), are an interesting outcome of the recognition of separate species. Accordingly, Paraschistorchis australiensisn. sp. is established to accommodate this Australian record. Given the detailed review and newly added data provided herein, we discuss the nature of the excretory vesicle within schistorchiines and amend the key to the recognized species of Paraschistorchis.