The Poriferan Skeletal System:
Sponges and Endoskeletons
Poriferans use a thin, porous, multi-cellular exoskeleton that provides them with both a form of protection as well as a means of allowing nutrients and wastes to move easily into-or-out of the inner body. Sponges make up this phylum and their exoskeletons are classified into 3 distinct patterns:
The honey-combed design of this species, Clathrina clathrus, is a pattern of exoskeleton formation found only in the class calcarea, which are found mostly in shallow tropical waters.
The barrel sponge is one of the many poriferan species belonging to the class demospongiae, with its skeleton made up of either the protein spongin or silica. Most poriferans belong to this class, about 90% in total.
This is Ceratoporella nicholsoni, a species belonging to the Sclerospongiae class, has a hard skeleton made of calcium carbonate. Members of this class are some of the oldest organisms, with some living to up to 1,000 years old.