The subfamily Polycerinae includes eight genera, from the monospecific Lamellana and Lecithophorus to the diverse Polycera and Gymnodoris, with 33 and 26 valid species, respectively. The monophyly of the subfamily has been tested by molecular data although not all genera were included. To date, relationships within the subfamily are not supported. In the present paper, three new species of polycerid nudibranchs are fully described based on specimens collected in Marshall Islands and Australia: one Palio species (Palio gaeli sp. nov.), one Polycera species (Polycera nimbsi sp. nov.) and a new genus (Paliota galactica gen. and sp. nov.). The new genus is described based on its peculiar radular teeth and genetic divergence.

The internal anatomy was studied by dissections and scanning electron microscope photographs. Partial sequences of mitochondrial cytochrome oxidase c subunit I (COI) and 16S ribosomal RNA (16S) as well as nuclear histone H3 (H3) were also obtained. A phylogenetic framework for two of these three species is proposed, also including for the first time the species Paliolla templadoi and Polycera melanosticta.

The alien nudibranch Polycera hedgpethi Er. Marcus, 1964, has been found in the Gulf of Cádiz (El Portil, Huelva). The present record in the Gulf of Cadiz could be considered an opportunity to connect the isolated Eastern Atlantic records for this species with those from the Mediterranean, even taking into consideration the possible unreported presence of this species along the North African Mediterranean coast. The collected specimens exhibited reproductive behaviour, suggesting the possibility of future additional records for this locality.