Figure 17.5 Formation of primmorph
from Stylissa massa cells after 3 hours
(A), 5 days (B) and 11 days (C)
aggregation.
particles are obtained (Figure 17.5C), the primmorphs. Primmorphs were observed more
closely with electron microscopy. Figure 17.6A shows the very smooth surface of such a
primmorph. Figure 17.6B shows a cross section, it can clearly be seen that the smooth
surface is like a skin around the reaggregated sponge cells. Primmorphs are usually a few
mm in size. Custodio et al. (1998) showed that cells inside the primmorphs showed a
high telomerase activity. This means that cells should be able to continue their cell
divisions.
The morphology of primmorphs resembles that of gemmules and buds, structures
found in many sponges in nature. Gemmules and buds are asexually-produced
reproductional stages that can be released by the parent sponge. The densely packed and
well-protected cells in gemmules and buds can survive long periods of starvation and low
temperature. When conditions are favourable again, the released gemmules and buds will
hatch; they attach to a solid surface and start to develop into functional sponges. The
striking morphological similarity between primmorphs and gemmules/buds, together with
the ability of primmorphs to be maintained under conditions of complete starvation for
long periods, has given rise to the idea that primmorphs are artificially created, axenic
resting stages. Although DNA replication in primmorphs has been demonstrated, growth
(of new biomass) has not yet been observed. Long term experiments with growth media
have not been conducted so far. Another important lesson about the development of cells
or primmorphs into functional sponges can be learned from older experimental sponge
embryology. By removing specific areas from larval tissue, it was demonstrated that at
least two cell types have to be present in sufficient amounts to allow further development:
Marine sponges as biocatalysts 517