The results suggest that although the collar of syconoid sponges may entrain flow around the surface of the choanocyte, uptake of particles greater than 0.
An exception may be the periflagellar sleeve of Suberites massa, a permanent sheath-like extension of the choanocyte surface (Connes et al.
What is unusual and intriguing, however, is the manner in which the choanocyte surface in Sycon coactum extends laterally and apically to phagocytose the latex microspheres or bacteria, and the observation that often several cells extend pseudopodia apparently for the same particle (e.
Given the high volumetric pumping rates recorded from demosponges (Reiswig, 1971; Vogel, 1974), it is unknown how particles remain stationary long enough in the choanocyte chamber of Sycon to be phagocytosed by pseudopodial extensions.
Choanocytes are flattened, but their central part projects into a gastral cavity.
Examination of a large number of electron micrographs revealed that the flagellated cells become the three principal cell types of juvenile sponges--that is, pinacocytes, scleroblasts, and choanocytes.
The choanocytes of juvenile sponges contain autophagosomes whose contents have been almost entirely digested.
As the gastral cavity develops, the choanocytes are flattened except at their thick central region.
We suggest that such amoeboid cells are precursor cells of choanocytes.
Minute ellipsoid granules were found in choanocytes that were still in the course of differentiation about 36 h after settlement.
In calcareous sponges, the consensus is that the choanocytes of juveniles derive from larval flagellated cells (Duboscq and Tuzet, 1937; Amano and Hori, 1993).
In cases where a supply of larval flagellated cells is not available, choanocytes can derive from archeocytes.