The blastopore and archenteron
were visible in the diminished vegetal half of chlorpyrifos-treated larvae.
erythrogramma, the gastrula forms a short archenteron
, and the gut remains incomplete and nonfunctional (Williams and Anderson 1975).
1F) may impede fusion of the tip of the archenteron
with the ectoderm and delay formation of the mouth in each species.
Our conclusion, based on the location of the chaetal sac, the folding of the archenteron
, and the relative locations of the stomodeum, anus, and chaetal sac in the earliest swimming larval stage, is that the blastopore becomes the opening immediately adjacent to the chaetal sac in the larva and thus forms the anus.
A "gastrula" would be of no functional importance, because the sponges lack sealed epithelia and extracellular digestion in an "archenteron
" would not be possible (Nielsen, 2008b).
In this type, the stomodeum fused to the anterior tip of the archenteron
and then the archenteron
differentiated into intestine, stomach, and esophagus.
During gastrulation, it appeared that one side of the embryo contributed more dark cells to the developing archenteron
than the other.
After secondary invagination, the gut rudiment results in a slender tube-like archenteron
However, the expression is not detected in the extending tip of the invaginating archenteron
, but remains at the blastopore region.
During reformation of the secondary pluteus, the epidermis covering the arms appears to be pulled towards the inner vee of the arms, presumably providing the cells for invagination and formation of the archenteron
. The epidermis appears buckled along the length of the arms and is pulled away from the ends of the skeletal rods.
The vegetal part of this gastrular epithelium invaginates to form the archenteron
[ILLUSTRATION FOR FIGURE 5D OMITTED], while the animal part of the epithelium becomes thinner [ILLUSTRATION FOR FIGURE 5B AND E OMITTED].
Gastrulae (24 h) have a spacious archenteron
and the blastocoel is a narrow space in which mesenchyme cells are evident [ILLUSTRATION FOR FIGURE 3A OMITTED].