J Mol Evol. 2004 Oct;59(4):448-57 doi:10.1007/s00239-004-2636-5

Edvardsen RB, Lerat E, Maeland AD, Flåt M, Tewari R, Jensen MF, Lehrach H, Reinhardt R, Seo HC, Chourrout D.

Hypervariable and highly divergent intron-exon organizations in the chordate Oikopleura dioica.

Study on housekeeping genes suggests that “Most Oikopleura introns occupy nonconserved positions and probably originate from numerous late intron gains or sliding of ancient introns”. Conservation within paralogs suggest possible gene conversion events.