Cover the sponges of the sea
Serving so many purposes
Besides looking rather bristly
are the skeletons of porifera. With multitudes of spicules covering
an average porifera, these needle-like projections facilitate the
purposes of protection and preservation. If spicules did not exist,
not only would sponges not possess a fossil record, but they would
be more susceptible to consumption by superior animals. Not to mention,
they would have no structure at all.
In order to be a sufficient
skeleton, spicules, extending from the interior to the exterior,
beyond the pinacocytes, need to be of a durable composition. These
fierce bristles also leave predators with a rather spiny problem.
Spicules are composed of an array of substances. The following are
Silica crystals can produce rather sharp spicules. However, in
a chlorine and bleach solution, and with other materials affecting
their composition, these spicules can actually dissolve. Such
is only observed with demosponges. Despite this, silica spicules
are extremely sturdy.
carbonate-Such spicules are theorized to only be characteristic
of the calcareous porifera, hence the name. It is extremely
hard and durable, so calcareous sponges form a more developed
fossil history. This material is also evident within pearls.
A pearl is formed when a grain of sand or other foreign object
ends up in the interior of an oyster. To end the irritation,
the oyster secretes a liquid of calcium carbonate. Slowly, layer
upon layer, a pearl is generated.
This is probably the most obvious of all the materials when
it comes to definition. Spongin in a fine fiber which circulates
water with facility. Usually, it is not found in nature as a
single constituent of spicules. Instead, it may be a component
of the inner layers of a spicule. Compounded forms of spongin
and silica are common substances in demosponge spicules.
Not only are spicules
practical for defense against predators, but when they are microscopically
viewed, they glisten and shine with an array of light. Silica spicules
have earned hexactinellids the name of glass sponges.