Mesopsammic polyclad members in the family Boniniidae have attracted attention in terms of their evolutionary shifts of microhabitat and their unique morphology such as a pair of pointed tentacles extending from the anterolateral margins and prostatoid organs harbouring stylets. Here, we establish a new species of this family as Boninia panamensis sp. nov. from the Pacific coasts of Panama, based on its morphological characteristics of (i) four cerebral and 61–80 marginal eyespots, (ii) two prostatoid organs located anterior and posterior to the penis papilla, and (iii) two uterine canals departing from the anterior part of the Lang’s vesicle. We also report Boninia cf. uru from Hawai’i, USA, based on its morphological identity with B. uru from Okinawa, Japan, along with their genetic distances for the partial cytochrome c oxidase subunit I (COI) sequences, which were beyond the range of intraspecific differences observed in congeners in this study. Boninia oaxaquensis is also reported from Panama as a new locality for the species. Involving the above-mentioned three species sequenced herein, we reconstructed molecular phylogenetic trees of Boninia based on the four gene markers (18S rDNA, 28S rDNA, 16S rDNA and COI). Our phylogenetic trees indicated the synapomorphy within the genus Boninia of the small numbers of stylets (2–4) and the connection route of the uterine canals to the Lang’s vesicle. The results also showed a characteristic distribution pattern in which pairs of species in distinct lineages occurred sympatrically with different microhabitats, as observed in Boninia uru and Boninia yambarensis in Okinawa and B. panamensis sp. nov. and B. oaxaquensis in Panama. In addition, we discuss possible speciation pathways in this genus based on the tree topology.

ZooBank: urn:lsid:zoobank.org:pub:D414BACD-C14A-4B34-8AF9-7ACBA28F46D0