Costasiellidae is a taxonomic family of small to minute sacoglossan sea slugs. These are marine opisthobranch gastropod mollusks. These sea slugs resembling nudibranchs, but are not closely related to them. This family has no subfamilies.
Species taxanomy provided by GBIF Secretariat (2022). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2023-06-13; License: CC BY 4.0