Bassham S, Postlethwait JH.

Development. 2005 Oct;132(19):4259-72. doi:10.1242/dev.01973

The evolutionary history of placodes: a molecular genetic investigation of the larvacean urochordate Oikopleura dioica.

Animals fed with algal concentrates. O. dioica has one orthologue of eyes absent, Eya, and one orthologue of the vertebrate Pitx genes, with multiple promoters and alternative splice sites, and lacking an OAR domain. It has three sine oculis orthologues, Six1/2, Six3/6a and Six3/6b. They are not clustered like vertebrate genes, but the two Six3/6 share an intron position in their homeodomain. Expression pattern of these genes support the hypothesis that O. dioica has a placode that is homologous to the vertebrate olfactory placode.