Sponges of the New Caledonian lagoon - IRD

Sponge
structure
s
ponge adults are generally incapable of locomotion, although we now
know of some remarkable exceptions to this rule. Survival largely
depends on the quality of the surrounding water and the loads of sediments
that rain down upon populations. The sponge animal obtains its
oxygen, nutrients and minerals for its skeleton from the ambient water column and
it excretes organic or mineral waste generated by its metabolism back into the
water. Since water moves continuously through the sponge its oxygen, mineral
salts and organic nutrient levels can change and vary qualitatively as well as quantitatively.
Each sponge species has a shape and an anatomy that is aptly suited to its
particular environment and prevailing hydrodynamic conditions. For example, in
shallow coastal waters with strong currents, surge and swell we find predominantly
soft-bodied species or flexible, whip-like growth forms that can literally bend with
the currents. In deeper waters where there is less dramatic movements of water
bodies hard-bodied, rigid sponges abound.
Porifera have a unique anatomy. Contrary to most other animals they have no
digestive tract, mouth or anus, nor any specialised organs or tissues. The sponge is
bounded on its exterior surface by a unicellular layer (exopinacoderm), composed
of special epithelial cells (pinacocytes). Some of these epithelial cells form small
external pores (ostia) through which water passes into the sponge, and others form
larger pores (oscules) through which water is expelled. Internally (the choanosome)
the sponge is excavated by water current canals, also lined by a single layer of
pinacocyte cells forming the endopinacoderm. The thin exterior layer of the
sponge, containing cells, the mineral and organic skeletons, is called the
ectosome. 'Water pumping stations' (choanocyte chambers) are found at certain
locations along the water canals, lined by special collar cells with a flagellum
(choanocytes), unique to the Porifera.
Sponges actively pump water into and out of their bodies using the differential
water pressures inside and outside the sponge. A water current is created by the
beating of many thousands of choanocyte f1agellae. Water is drawn in through the
multitude of small ostia or pores, with diameter less than a few tenths of a millimetre,
and pumped through the water filtration system with its series of sieves or
filters of diminishing size, which serve to extract larger particles from the seawater.
These water canals connect directly or indirectly to choanocyte chambers, in which
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Sponge
structure