Julia thecaphora (Carpenter, 1857) Page Two
The nomenclatorial and systematic vagaries of Juliidae E.A. Smith, 1885 (1871)
Prasina borbonica Deshayes, 1863 is the basis for the genus Prasina Deshayes, 1863 (monotypy) and the family Prasinidae Stoliczka, 1871. Juliidae E.A. Smith, 1885 is based on Julia Gould, 1862a1 [Type: J. exquisita Gould, 1862a ¹ ² (monotypy), a subjective synonym of P. borbonica; see Kay (1968)] post-dates Prasinidae, yet the valid family name is Juliidae.
Why is that you might ask. Well over a century ago workers such as Dall recognized the synonymy of Julia and Prasina (and/or their type species) and began to employ Julia (and often Juliidae), based on the priority of its type species, instead of the earlier synonym Prasinidae. Although the type genus of the family is clearly Julia, the valid family name does not necessarily have to be formed from the same stem as its type genus (Article 40.1 of The Code [ICZN, 1999]). Based on this provision, Prasinidae seems to have a lock on the correct family name for this group of bivalved sacoglossan gastropods. However, as we have witnessed many times, the ICZN allows certain exceptions. Article 40.2 reads "If, however, a family-group name was replaced before 1961 because of the synonymy of its type genus, the substitute name is to be maintained if it is in prevailing usage." Not only that, the substitute enjoys the same priority as the replaced name (Article 40.2.1)
For nearly a century members of the family were regarded as bivalves. After living juliids were collected on the Caulerpa in Japan, it became apparent that these mollusks are in fact unusual sacoglossan opisthobranch gastropods with a two-part shell. Observations on the referent living juliid, Tamanovalva limax Kawaguti and Baba, 1959, revolutionized our understanding of the group (Kay, 1968), which reaches back to the Eocene (Burn, 1998). The latter reference gives a nice summary of the biology of the group.
¹ Original descriptions, as reproduced in Gould,
1862b (241), are shown below.
Brann, D.C., 1966. Illustrations to "Catalogue of the collection of Mazatlan shells" by Philip P. Carpenter. Paleontological Research Institution, Ithaca, NY. (1)-111 + 60 plates. 1 April.
Burn, R., 1998. Family Juliidae. Pp. 964-966 in Beesley, P.L., G.J.B. Ross, and A. Wells [eds.]. Mollusca: the Southern Synthesis. Fauna of Australia. Vol. 5 part B. CSIRO, Melbourne. i-vii + 565-1234.
Carpenter, P.P., 1857. Catalogue of the collection of Mazatlan shells in the British Museum collected by Frederick Reigen, described by Philip P. Carpenter. British Museum, London (i)-xii + (1)- 552. After April 21.
Gould, A.A., 1862a. Descriptions of new genera and species of
shells. Proceedings of the Boston Society of Natural History 8:
280-284. Feb. <http://www.biodiversitylibrary.org/item/37036#page/293/mode/1up>.
(International Commission for Zoological Nomenclature), 1999.
International code of zoological nomenclature fourth edition.
International Trust for Zoological Nomenclature, London. pp. 1-306 +