peruvianum, IMPLBA033 from Peru, and in none of the A. ostenfeldii strains. The suitability of this character for identification of A. peruvianum has been previously challenged, e.g., by Lim et al. (2005), who found a large number of cells with a straight margin in material from Malaysia that otherwise agreed with the A. peruvianum description. Balech (1995) similarly reported a mix of straight and curved margins in material from North America; however, he considered this an exception. The s.a. plate, which has commonly been considered the most important feature

for the delineation of A. peruvianum from A. ostenfeldii (Balech 1995, Lim et al. 2005, Bravo et al. 2006, Touzet et al. 2011, Tomas et al. 2012), was also found to be problematic. Most of the A. peruvianum isolates Cisplatin contained significant selleck inhibitor amounts (20%–30%) of the door-latch shaped s.a. plates typical for A. ostenfeldii. A-shaped “A. peruvianum”- s.a. plates, in turn, were present in most A. ostenfeldii strains, often >40% of the cells from the same culture frequently exhibited this feature. Such reverse s.a. distributions were furthermore observed in closely related strains from the same geographic population. In the Baltic Sea, for example, the geographically and genetically close strains AOKAL09 and AOVA17 had 20% and 67% A-shaped s.a.

plates, respectively. Such intra-strain and within population/group variability also calls into question the applicability of the s.a. shape as a distinctive character. Finally, distinctive A. peruvianum features rarely occurred in combination, i.e., A-shaped s.a. plates were not necessarily accompanied by small ventral pores or smaller cell size. Our observations on extensive material from a large global sample set emphasize that the present morphological delineation of A. peruvianum from A. ostenfeldii is not well supported. Together, phylogenetic and

morphological data suggest that A. peruvianum should not be considered a distinct species, and that the name should be treated as synonym of A. ostenfeldii. Each of the analyses returned six phylogenetic groups. These results were consistent with previous phylogenetic analyses based on either concatenated rDNA (Orr et al. 2011) or LSU D1-D2 (Anderson et al. 2012) sequences. Typically, the groups fell into two main clusters, with those Vasopressin Receptor corresponding to groups 4, 5 and 6 forming one and groups 1 and 2 another. Prior to the more detailed analysis in this study, it had been suggested that the A. ostenfeldii complex contained two major genetic groups or genotypes (Touzet et al. 2008, Kremp et al. 2009) that may even coexist (Touzet et al. 2008). The results of this study indicate that instead of two clearly differentiated genotypes, the groups represent a continuum of ribotypes which are differentiated both morphologically and genetically from one another by varying degrees.