Seven species of Halgerda were described in the years 1880-1905, two species in 1932-1949, four species from 1975-1982, then 22 species in the years 1993-2001. In 2018 another six new species were described from Mozambique, highlighting the number of undescribed species on the African coast of the Indian Ocean.Tibiriçá, Y.; Pola, M.; Cervera, J. L. (2018). Systematics of the genus Halgerda Bergh, 1880 (Heterobranchia : Nudibranchia) of Mozambique with descriptions of six new species. Invertebrate Systematics. A number of undescribed species are known and many species show considerable variation across their ranges, which may indicate that more cryptic species exist.Gosliner, T.M., Behrens,D.W. & Valdes,A., 2008. Indo-Pacific Nudibranchs and Sea Slugs. A field guide to the World's most diverse fauna. Sea Challengers Natural History Books & The California Academy of Sciences.
