Derelle R, Momose T, Manuel M, Da Silva C, Wincker P, Houliston E.

RNA. 2010 Apr;16(4):696-707. doi:10.1261/rna.1975210

Convergent origins and rapid evolution of spliced leader trans-splicing in metazoa: insights from the ctenophora and hydrozoa.

“First evidence for SL trans-splicing in ctenophores.” (Pleurobrachia pileus and Mnemiopsis leidyi) “Analysis of data sets for the hydrozoans H. magnipapillata and C. hemisphaerica revealed a high number of SL sequence variants per species.” The same gene may use different splice leaders. An adenosine-rich region is found between the trans-splicing site and the transcription initiation site in hydrozoans, but not in other species (including Oikopleura.