Fine structure of clonally propagated in vitro life stages of a Perkinsus sp isolated from the baltic clam Macoma balthica

We established monoclonal in vitro cultures of a Perkinsus sp. isolated fro m the baltic clam Macoma balthica and compared morphological features of va rious life stages by light and transmission electron microscopy to those of the currently accepted Perkinsus species: Perkinsus marinus, Perkinsus ols eni. Perkinsus atlanticus, and Perkinsus qugwadi. Except that trophozoites were slightly larger than those of P. marinus, and that they underwent zoos porulation in culture, observation of our isolate under light microscopy di d not reveal striking differences from any Perkinsus species. Perkinsus sp. from M. balthica shared fine structural characteristics with other Perkins us species that clearly place it within this genus. Although zoospores of P erkinsus sp. from M. balthica were slightly smaller than those from other s pecies, the ultrastructural arrangement and appearance of the epical comple x and flagella seem to be identical to those of P. marinus and P. atlanticu s. Our isolate also appeared, in some sections, to have cortical alveolar e xpansions of the plasmalemma at regions other than the anterior end and lob ulated mitochondria that were reported as unique for P. qugwadi Little cons ensus exists among authors in the assignment of taxonomic weight to any par ticular morphological feature to designate Perkinsus species. The present s tudy of gross morphology and ultrastructure was complemented with molecular studies reported elsewhere, which propose that Perkinsus sp. from Macoma b althica is a distinct species.