Cylinder-scales in marine flagellates from the genus Chrysochromulina (Haptophyceae = Prymnesiophyceae): further observations from C. microcylindra Leadbeater and C. cyathophora Thomsen

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Abstract
As aids to the phyletic interpretation of the newly described Chrysochromulina pachycylindra Manton et al., some hitherto unrecorded gatherings of C. microcylindra Leadbeater and C. cyathophora Thomsen, from South Africa and South Alaska respectively, are introduced, thereby amplifying the type descriptions of both species, which were previously known only from Europe. Characters shared between C. pachycylindra and C. microcylindra are numerous, including a capacity for transverse fracture of their cylinders not previously noted in the latter. This suggests an exceptional degree of affinity between these two species in spite of gross differences in relative dimensions of different parts of their respective cylinder scales. On the other hand the general resemblance between C. microcylindra and C. megacylindra (Leadbeater, 1972), previously noted, is unaffected by these findings and it is concluded that all three species could be treated as a closely related subgroup within the genus Chrysochromulina. In contrast, C. cyathophora is shown to be so different as to be interpretable only in terms of parallel evolution from a separate prototype source, the plate-scales in particular being so far unique in the genus in being thin, rimless, peculiarly patterned and convex when seen in section. The mere presence of cylinder-scales is thus seen to be insufficient evidence of phyletic affinity unless confirmed by other characters, among which the details of the plate-scales are probably the most important.