Amazingly, half of the sponge's
choanocyte (filtration) cells had divided and the
choanocyte's cell division cycle was a phenomenally short 5.4 hours.
In the calcareous sponge Sycon coactum, water enters through pores 10-20 [micro]m apart into long chambers lined by several thousand pumping choanocytes (Fig.
Pieces of fractured choanocyte chambers were surveyed for interactions between particles and choanocytes.
Choanocytes of all sponges fixed 5-10 min after being fed were already filled with phagosomes containing either beads or bacteria, suggesting that uptake occurs within only a few minutes of particles entering the animal.
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).
About 36 h after settlement, choanocytes are differentiated in the inner cell mass and formation of the choanocyte chamber begins.
Choanocytes. Choanocytes derive from the cells of an inner cell mass.
piceus: the adjacent
choanocyte chambers are destroyed, and some of the
choanocytes degenerate.
In this report, we show that larval flagellated cells transform into choanocytes during metamorphosis.
Minute ellipsoid granules in amoeboid cells and choanocytes
As in the present study, the development of sperm from archeocytes has been documented among other sponges as well, although spermatozoids are generally thought to develop from choanocytes (Reiswig, 1983).
In addition, the absence of a periflagellar sleeve from around the base of the choanocyte's flagellum, which is typical of hadromerid sponges (Vos et al., 1991), also strengthens this view.
