periplast

Additionally, the cell body of many choanoflagellates is surrounded by a distinguishing extracellular matrix or periplast.

Large ejectisomes, visible under the light microscope, are associated with the pocket; smaller ones occur underneath the periplast, the cryptophyte-specific cell surrounding.

The functional significance of the periplast is unknown, but in sessile organisms, it is thought to aid in attachment to the substrate.

In planktonic organisms, there is speculation that the periplast increases drag, thereby counteracting the force generated by the flagellum and increasing feeding efficiency.

Previously, Choanoflagellida was divided into these three families based upon the composition and structure of their periplast: Codonosigidae, Salpingoecidae and Acanthoecidae.

Choanoflagellates are either free-swimming in the water column or sessile, adhering to the substrate directly or through either the periplast or a thin pedicel.

Members of the family Codonosigidae appear to lack a periplast when examined by light microscopy, but may have a fine outer coat visible only by electron microscopy.

They are characterised by chloroplasts containing Cr-phycoerythrin 545, and an inner periplast component (IPC) comprising "a sheet or a sheet and multiple plates if diplomorphic".

Euglenids are distinguished mainly by the presence of a pellicle (periplast), which is composed of proteinaceous strips underneath the cell membrane, supported by dorsal and ventral microtubules.