An ocean yet to be discovered: increasing systematic knowledge of Indo-Pacific Okenia Menke, 1830 (Nudibranchia : Goniodorididae).

Numerous faunistic and ecological studies have been conducted throughout the Indo-Pacific Ocean to assess its biodiversity. Despite the abundance of research, studies on the species that inhabit the Indo-Pacific are still necessary due to its extent and high species richness. The major species richness of the genus Okenia Menke, 1830 (Nudibranchia, Goniodorididae) is found in the Indo-Pacific Ocean, including 38 of 60 valid species. Nevertheless, this number does not represent the real biodiversity, since at least 20 more species are already reported in field-guides as undescribed species belonging to this genus. The systematics of the genus Okenia are still unclear since it has been the subject of only a few and incomplete studies. In the present paper, we describe five new Okenia species from the coastlines of Japan, Mozambique and Australia: Okenia aurorapapillata sp. nov., Okenia elisae sp. nov., Okenia nakanoae sp. nov., Okenia siderata sp. nov. and Okenia tenuifibrata sp. nov. Moreover, anatomical details not previously described of Okenia atkinsonorum , Okenia barnardi , Okenia cf. echinata , Okenia hallucigenia , Okenia hiroi , Okenia japonica , Okenia pellucida , Okenia pilosa and Okenia rhinorma are provided. New partial sequences of standard markers (COI , 16S rRNA and H3) were obtained and a phylogenetic analysis that included all species with available data was performed. ZOOBANK urn:lsid:zoobank.org:pub:28AE2536-A264–4194–8AE3-C430620572E7 Currently, the largest number of known Okenia species are inhabiting the Indo-Pacific. However, ~20 species are still reported as undescribed in field-guides to this genus. In the present paper, we obtain new DNA sequences for Okenia species and study their evolutionary relationships. Moreover, we describe five new Okenia species from the coastlines of Japan, Mozambique and Australia: Okenia aurorapapillata sp. nov., Okenia elisae sp. nov., Okenia nakanae sp. nov., Okenia siderata sp. nov. and Okenia tenuifibrata sp. nov. [ABSTRACT FROM AUTHOR]