DAO 58:231-244 (2004)  -  doi:10.3354/dao058231

Perkinsus mediterraneus n. sp., a protistan parasite of the European flat oyster Ostrea edulis from the Balearic Islands, Mediterranean Sea

Sandra M. Casas1, Amalia Grau2, Kimberly S. Reece3, Kathleen Apakupakul3, Carlos Azevedo4, Antonio Villalba1,*

1Centro de Investigacións Mariñas, Consellería de Pesca e Asuntos Marítimos, Xunta de Galicia, Apartado 13, 36620 Vilanova de Arousa, Spain
2Estación de Acuicultura, D. G. Pesca, Govern Balear, Port d¹Andratx, Mallorca, 07158 Spain
3School of Marine Science, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062, USA
4Department of Cellular Biology, Institute of Biomedical Sciences, University of Oporto, Porto 4099-003, Portugal
*Corresponding author. Email:

ABSTRACT: A new species, Perkinsus mediterraneus, a protistan parasite of the European oyster Ostrea edulis (L.), farmed along the coast of the Balearic Islands, Mediterranean Sea, is described. Morphological examinations with light and transmission electron microscopy, DNA sequence-analysis and enlargement in Ray¹s fluid thioglycollate medium (RFTM) confirmed that this parasite belongs to the genus Perkinsus. Specific morphological and genetic characteristics indicated that it should be considered a new species in the genus. Sequencing of the small subunit ribosomal (ssu rRNA) gene confirmed that the parasite belongs to the genus Perkinsus, and sequences of the internal transcribed spacer (ITS) were distinct from any Perkinsus ITS sequences previously published and/or deposited in the GenBank. Phylogenetic analysis revealed that the ITS sequences of the new species formed a monophyletic group comprising a sister clade to the P. atlanticus/olseni group. In addition, morphological differences were observed between the new species and the other described Perkinsus spp.. After incubation in RFTM for 1 wk, the prezoosporangium had reached an extremely large size (97.4 ± 1.99 µm) (mean ± SE), and after 2 wk incubation had again almost doubled in size (167.1 ± 8.09 µm). The discharge-tube length was one sixth the diameter of the zoosporangium, i.e. a ratio of 17.36:97.38, the lowest ratio observed for any Perkinsus species. At the ultrastructural level, zoosporangia and zoospores exhibited some differences compared to other Perkinsus species.


KEY WORDS: Perkinsus mediterraneus n. sp. · Ostrea edulis · Oyster parasite · Ultrastructure · Zoosporulation · ssu rRNA gene · Internal transcribed spacer · Perkinsus atlanticus


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