Blackish slugs with a wide body and a length of about 10
mm were discovered on the mud and in small pools in a
mangrove forest in the Pak Phanang Bay (Gulf of Thailand).
When noting that they had a notum with a wide free border,
the slugs were believed to be young specimens of the family
Onchidiidae. That idea was rejected when the expanded
head showed no stalked eyes, but internal eyes like those of
the sacoglossan Limapontia spp. After leaving the mosquito
saturated mangrove forest for taking a better view in the
lab, it appeared that the species could not be allocated to
any family known to the authors. Therefore, the slugs were
studied in more detail. As no description of a family, genus,
or species was found of which the characteristics fi t with
our slugs, the family, genus, and species are described as
new in this paper.