Cylindrocapsa is a genus of green algae, specifically of the Chlorophyceae.

[2] Virus-like particles have been found in a strain of one species, Cylindrocapsa geminella.

[3] Cylindrocapsa consists of unbranched filaments, often attached to substrates or free-floating in water.

Cells are initially uniseriate (that is, in one line), but may later become multi-seriate or irregularly arranged.

Individual cells are ovoid to oblong to spherical, and are each surrounded by several concentric layers of a mucilaginous sheath.