The flagellar axoneme observed in the amoeboid cells is evidently the one that was retracted in the cell body of the flagellated cells. The alternative possibility - that it may represent a flagellated cell phagocytosed by other larval cells or archeocytes - is excluded for the following reasons.
In calcareous sponges, larval flagellated cells are transformed into the choanocytes of a juvenile during metamorphosis (Duboscq and Tuzet, 1937; Amano and Hori, 1992, 1993).
Because larval flagellated cells change radically in morphology in the early stages of metamorphosis, it is almost impossible to follow their developmental fates unless the cells have some identification markers.
Returning to motile cells, the flagellated cells
of charophytes have a unilateral (asymmetrical) flagellar rootlet system.
The more derived groups of fungi--zygomycetes, ascomycetes, and basidiomycetes--are all predominantly filamentous and terrestrial, and lack flagellated cells
at any stage of the life cycle.
These pores open into chambers that are lined with layers of flagellated cells
that are constantly in motion.
Detailed electron microscopic studies on the metamorphosis of the coeloblastula revealed that the larva consists of four types of cells: flagellated cells, bottle cells, vesicular cells, and free cells in a central cavity.
The layer of flagellated cells is a larval organ for swimming, therefore those cells disappear soon after settlement.
After settlement, the larval flagellated cells dedifferentiate into a simple cell mass on the substratum; thereafter they differentiate again into the three principal cell types of a juvenile sponge.
The fate of the flagellated cells has long been discussed.
Peripheral flagellated cells showed an intense brown stain with the con A probe for mannose [ILLUSTRATION FOR FIGURES 1A,B OMITTED], but only a weak stain with GlcNAc [ILLUSTRATION FOR FIGURE 1C OMITTED], and no stain at all with the other lectins tested (SBA, DBA, PNA, UEA-1) (not shown).
The brown staining of fragmented DNA produced by the TUNEL assay indicated that apoptosis was only located in the peripheral region of flagellated cells. However, brown staining was sometimes seen within large cells adjacent to the peripheral region [ILLUSTRATION FOR FIGURE 1D OMITTED], suggesting that apoptotic cells or fragments had been engulfed by large phagocytic cells (probably archaeocytes).