See text Costasiellidae is a taxonomic family of small to minute sacoglossan sea slugs.

These are marine opisthobranch gastropod mollusks belonging to the superfamily Plakobranchoidea.

[1] These sea slugs resembling nudibranchs, but are not closely related to them.

This family has no subfamilies.

The following genera belong to the family Costasiellidae: