Detection of Prorocentrum shikokuense in the Mediterranean Sea and evidence that P. dentatum, P. obtusidens and P. shikokuense are three different species (Prorocentrales, Dinophyceae)

A dinoflagellate identified as Prorocentrum dentatum, P. shikokuense or P.donghaiense is responsible of massive harmful events. Blooms of a species identified asP. shikokuense have been recently reported in the Mediterranean Sea, and an exoticorigin, tentatively introduced by ballast waters from Asia, has been hypothesized. Themolecular data based on the small-, large subunit, and internal transcriber spacersribosomal RNA gene (SSU-, LSU-, ITS rRNA) sequences confirmed P. shikokuense inthe Mediterranean Sea. The Mediterranean ribotype is identical to a subtropical NorthAtlantic ribotype, and with slight divergence from the numerous sequences from thePacific Ocean. To revisit the relationship between P. shikokuense (=P. donghaiense)and P. obtusidens, we provide the first micrographs of P. dentatum and P. obtusidens,the latter collected from the type locality. Our observations indicate that P. dentatum, P.obtusidens, and P. shikokuense are three different species. Their diagnosticmorphological characters are: Prorocentrum dentatum is 44-60 ?m long, leaf-shaped,pointed and central posterior end, conspicuous anterior shoulder; P. obtusidens is 33-41?m long, irregular parallelepiped, almost parallel valve margins, eccentric and pointedposterior end, moderate anterior shoulder; and P. shikokuense is <25 ?m long,sunflower seed-shaped, round and centric posterior end, inconspicuous anteriorshoulder.