Although many uncertainties still exist about sponge cell biology, the general view is that
sponge cells can reversibly alter their function, with only a few cell types being
terminally differentiated. For example, a pinacocyte can become an archaeocyte and vice
versa. This feature and the low organisational level of the sponge body are responsible
for another important property of sponges: their strong regenerative power. It was
discovered a long time ago that cuttings of mature sponges can regenerate into full-
grown, functional sponges. This property is important for biotechnology: cloning of
sponges is much easier than cloning of higher animals.
In addition to their ability to reproduce asexually, sponges also have sex. Formation
and release of eggs and sperm cells occurs. Some sponge species are hermaphrodite, egg
and sperm production taking place within the same individual. Other species have male
and female individuals, which both release their gametes into the surrounding water so
that fertilisation takes place outside the sponge body.
Sponges are filterfeeders: they filter small organic particles (microalgae, bacteria, dead
organic particles) out of the surrounding water. It is generally assumed that the upper size
limit of particles that can be taken up (i.e. the size of the inflowing pores) is around 50
μm. Larger particles are trapped where the inflowing channels become narrower. The
particle is then ingested by an archaeocyte cell via phagocytosis. After taking up the
particle, the archaeocytes move through the mesohyl matrix towards an outflowing
Figure 17.3 Body structure of a
sponge. A. Macroscopic observation.
B. Cross-section, showing a canal
system through which media is
Multiphase bioreactor design 510