Trilobovarium aicsuem sp. nov. (Digenea: Opecoelidae) from Northern whiting Sillago sihama (Fabricius, 1775) in Maputo Bay, Mozambique, based on an integrative systematic approach, and notes on genus diagnosis

The erection of Trilobovarium Martin, Cutmore & Cribb, 2017 was based on combined evidence from morphology, molecular data, host ecology and biogeography. Currently, four species are known from the Indian Ocean: Trilobovarium krusadaiense (Gupta, 1956) from India, Trilobovarium lineatum (Aken’Ova & Cribb, 2001) from Western Australia and Trilobovarium diacopae (Nagaty & Abdel Aal, 1962) and Trilobovarium khalili (Ramadan, 1983) reported from the Red Sea. Opecoelid trematodes were collected from the intestine of Sillago sihama (Fabricius, 1775) along the shore of Inhaca Island (Maputo Bay) and determined to represent a new taxon based on an integrative taxonomic approach. Trilobovarium aicsuem sp. nov. differs from all congeners by its long body and a cirrus-sac that extends posteriorly beyond the ventral sucker. It is morphologically similar to T. khalili but differs in having an ovary with three lobes vs. an ovary with six to nine lobes, and an excretory vesicle extending to the level of the anterior testis vs. to the posterior testis. However, T. aicsuem has an egg count ranging from 22 to 76, which is unusual as the genus is, in part, distinguished from Neolebouria Gibson, 1976 based on a smaller number of eggs (< 30). Genetic data based on 18S, ITS2 and 28S rDNA indicate a closer relation of T. aicsuem to Podocotyloides parupenei (Manter, 1963) than to Trilobovarium parvvatis Martin, Cutmore & Cribb, 2017, even though the latter taxon is still closely related to the new species. Based on the results presented here, the diagnostic criteria for Trilobovarium are expanded slightly (< 80 eggs). The inclusion of P. parupenei in the ingroup of Trilobovarium taxa based on the included markers, despite the clear morphological difference, needs further attention. This is the first report of a Trilobovarium species infecting a sillaginid fish along the southeastern coast of Africa, being the fifth report of this genus in the Indian Ocean.