The subfamily Emarginulinae, common name keyhole limpets and slit limpets, is a taxonomic subfamily of limpet-like sea snails, marine gastropod molluscs in the family Fissurellidae, the keyhole limpets and slit limpets.
The subfamily consists of the following tribes:Tribe Emarginulini Children, 1834 - synonyms: Rimulidae, Anton, 1838; Zeidoridae Naef, 1913; Hemitominae Kuroda, Habe & Oyama, 1971; Clypidinidae Golikov & Starobogatov, 1989 Tribe Diodorini Odhner, 1932: this tribe has been raised to the rank of subfamily Diodorinae Odhner, 1932 Tribe Fissurellideini Pilsbry, 1890 Tribe Scutini Christiaens, 1973
Of the three subfamilies in Fissurellidae, the subfamily Emarginulinae is the oldest: its earliest known species date back to the Mesozoic.
The various tribes belong to this subfamily because of the unifying features in their radula. Several tribes were formerly accepted as subfamilies, because of the differences in their shell. The Emargulini have a caplike shell with a slit in the margin but without an apical opening (foramen). The Scutini have a flat shield-shaped shell with a vague indentation at the back. The other tribes have a caplike shell with a round, oval or triangular apical opening.
The species of this subfamily can be found attached to rocks or coral. They are Herbivores.