Cosmarium hexalobum. Notice trapeziform outline of semicells and deeply cerenate margins.
Cell dimensions (L x B): 37 x 31 µm

Empty cell of Cosmarium hexalobum showing pairs of radiating series of granules linked to the marginal crenations as well as supraisthmial, longitudinal rows of verrucae.



Desmid of the month
December 2019

Cosmarium hexalobum

Cosmarium hexalobum somewhat resembles C. caelatum. Like that latter species, cells of C. hexalobum are marked by deeply crenate margins and a supraisthmial inflation ornamented with longitudinal, parallel rows of verrucae. Marginal crenations are bigranulate and linked with paired radiating series of intramarginal granules. Compared with C. caelatum, however, semicells in C. hexalobum are distinctly trapeziform instead of subrectangular. In the Netherlands, C. hexalobum, having a predominantly arctic-alpine distribution, is a rare species that is only known from some sites in the northern part of the country.

SEM picture of Cosmarium hexalobum showing cell wall sculpturing in more detail.