Pieces of fractured choanocyte chambers were surveyed for interactions between particles and choanocytes.
The structure of choanocyte chambers and morphology of cells and particles were identical in sponges fed in situ and in vitro.
At the apical surface each choanocyte has a 15-[micro]m-long flagellum that is surrounded by a ring of microvilli (Fig.
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.g., Fig.
One view holds that the flagellated cells are transformed into the choanocytes of juvenile sponges (Borojevic and Levi, 1965; Boury-Esnault, 1976; Amano and Hori, 1994, 1996), but the opposing view contends that they are lost by exfoliation or phagocytosis during metamorphosis (Bergquist and Glasgow 1986; Misevic et al., 1990; Kaye and Reiswig, 1991).
Choanocytes. Choanocytes derive from the cells of an inner cell mass.
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. This conclusion is supported by the fact that these three cell types contain glutinous granules, which only the flagellated cells have in the free-swimming larva.
In this report, we show that larval flagellated cells transform into choanocytes during metamorphosis.
Minute ellipsoid granules in amoeboid cells and choanocytes
We suggest that such amoeboid cells are precursor cells of choanocytes.
The new sponge has neither
choanocytes nor a system for filtering water.
