|The Sponge -
enigma of nature First published in the 'Nassau
With the exception of
the single - celled animals, the Protozoa, the sponges
are the simplest animals in existence today. In fact,
they are so unusual that scientists for hundreds of
years were uncertain exactly what they were.
As long as 2,000 years ago Aristotle recognised the
nature of sponges, but only in the last 200 years have
all scientists come to accept this view. Like sea fans
and other soft corals, sponges were thought to be plants
by most people, a few even thought that they were
solidified sea foam or the homes of marine worms!
In 1766 John Ellis discovered
that they eject currents of water and must therefore be animals,
however, as recently as 1841 some scientists were still arguing
before the Royal Society that sponges were plants. Even today,
in this age of enlightenment, many people do not really know
what sponges are, considering them only in the context of the
Much early misconception arose from the fact that studies were
carried out on freshwater sponges, many of which have within
their tissues single celled plants giving them a green
colouration. Their shape is also, in many cases, plant-like.
Despite the fact that sponges have in some cases muscle 'fibres'
and even nerve cells, some scientists still do not think of them
as true animals but place them in a separate sub-kingdom, the
|Whatever their true
relationship with the rest of the Animal Kingdom,
sponges are nonetheless successful in their own right.
In the Bahamian seas, sponges are one of the most
dominant groups in terms of total mass (Biomass),
probably running a close second to the corals.
All animals in the sea are ultimately dependant upon
plants, for only plants can make organic food from
simple substances like carbon dioxide and water by using
the energy of the sun. The majority of such plants in
the sea are the tiny single-celled members of the
plankton, drifting by their countless millions in the
upper layers of the sea. These provide food for the
filter feeders like the corals and the sponges.
Sponges vary greatly in size,
shape and structure. The largest sponge is the Loggerhead
sponge, Spheciospongia vesparium, which may grow to the size of
a small barrel. Such a large sponge may contain hundreds of tiny
animals living within its tubes and chambers, including worms,
shrimps, molluscs, starfish and even small fish.
Structurally, the simplest sponge is a tube with its upper end
open. Hundreds of small pores in the walls of this tube lead in
to what are known as flagellated chambers. Each of these
chambers is lined by numerous tiny cells, each bearing a long
whip which beats and creates the water current passing in toward
the central chamber of the sponge. These cells also remove small
food particles from the water, which are passed on to other
||Many of the cells
within a sponge are capable of surviving independently.
One classic experiment involves forcing a sponge through
a fine silk, so breaking it up into the smallest parts.
After this was done the sponge cells re-aggregated on
the other side of the silk to produce new colonies.
Reproduction, as in other simple organisms, is by
various methods. Usually a larva is released which swims
for some 24 hours before settling on the bottom to begin
the formation of a new sponge colony.
The skeleton of a sponge may consist of a complicated
network of fibres, as in the commercial sponges, or of
many small spicules embedded in the tissues. These
spicules may be made of silica or of calcium carbonate,
and may assume the form of forks, anchors, needles stars
or a variety of other shapes.
Frequently the identity of
the sponge may only be determined by microscopic examination of
these spicules. The common names of sponges are usually fairly
For instance, there
is the bleeding sponge which gives off a blood red
liquid when squeezed, the stinker sponge, which has a
strong unpleasant odour; and the Do-Not-Touch-Me Sponge
whose Latin specific name 'nonlitangere' means precisely
that, on account of the fact that when handled it may
cause severe burning and blistering. Sponges have a
worldwide distribution, being found in both fresh and
salt water, and even in lakes in the craters of extinct
volcanoes. Nowhere, however,
do the sponges attain the number and variety that they
do here in the shallow warm waters of the Bahamas.