Tetmemorus laevis
Image © Koos Meesters

Cell of Tetmemorus laevis. Notice the apical incision characteristic of the genus Tetmemorus

Cell dimensions (L x B): ca 85 x 25 µm

 

 

 

Desmid of the month
February 2009

Tetmemorus laevis

Tetmemorus laevis roughly resembles T. granulatus being characterized by fusiform cells and a pattern of scattered cell wall pores. On closer examination cells of T. laevis usually are smaller and less strongly tapering to the poles than those of T. granulatus. The most essential difference, however, is in the shape of the zygospore: globose in T. granulatus, oblong with conical angles in T. laevis.

In the Netherlands T. laevis is rather common in fens and bogs, preferably occurring in Sphagnum cushions where it can stand periodical desiccation. Zygospores are occasionally encountered.

Tetmemorus laevis, conjugation Image © Henk Schulp

T. laevis, conjugation

Tetmemorus laevis, immature and maturuezygospore
Image © Koos Meesters

Immature (on the left) and mature (on the right) zygospore of T. laevis. In the immature spore still the 4 chloroplasts of the former gametangial cells are to be distinguished. Some of the conical angles of the spore extend into the empty semicells.

In the mature spore on the right the plasmatic cell content has aggregated into a  rounded mass bordered by a thick, brownish wall, enclosed by an empty, rectangular envelope.

Tetmemorus laevis, mass development of zygospores Image © Koos Meesters

Mass development of T. laevis zygospores