Drawing

Description:

Bicosta spinifera (Throndsen, 1970) Leadbeater, 1978. Choanoflagellates with a lorica consisting of two longitudinal costae which cross over in the middle of the lorica chamber, two anterior spines diverging at an angle of about 60 degrees, and a long posterior spine with a hook-like curve near the distal end. However, most loricas had a shorter, almost straight posterior spine and anterior spines diverging at an angle of about 120-135 degrees. The longitudinal costae of the latter type of cells are either crossed over in the normal position or crossed over closer to the posterior spine, and occasionally do not cross over at all. The lorica length varies from 45-55 microns in normal cells and from 23-34 microns in individuals with a wide angle between the anterior spines. The shorter variant with less distinct cross over may be difficult to distinguish from Bicosta minor.