Introduction - Porifera
Poriferans are commonly referred to as sponges. An early
branching event in the history of animals separated the sponges from other
metazoans. As one would expect based on their phylogenetic position, fossil
sponges are among the oldest known animal fossils, dating from the Late
Precambrian. Since then, sponges have been conspicuous members of many fossil communities; the number of described fossil genera exceeds 900. The
approximately 5,000 living sponge species are classified in the phylum Porifera, which is composed of four distinct groups or classes, the Hexactinellida (glass sponges), the Demospongiae, the Calcarea (calcareous sponges), and the Sclerospongiae (smallest kind).
Nervous System - Porifera
The nervous system of the Porifera is very simple. There is no nervous system of the Porifera. For other non spongey porifera there are elaborate nervous systems, but in sponges the vital nervous system for many other animals is not present.
The living sponges of today are grouped into four different classes, according to their skeletal structure, which serves for protection, stiffening, and support:
Class Calcarea
![Picture](/uploads/1/1/5/0/11508385/1336084702.jpg)
The skeleton consists of individual spicules of calcium carbonate .
Class Hexactinellida
![Picture](/uploads/1/1/5/0/11508385/9601957.jpg?373)
These members have spicules of silica fused in a continuous and often very beautiful latticework. There are also known as the glass sponge.
Class Demospongiae
![Picture](/uploads/1/1/5/0/11508385/9864599.gif?319)
This Porifera is the largest class, which has unfused silica
spicules, OR a tough, keratin-like protein called spongin, or a
combination of the two
spicules, OR a tough, keratin-like protein called spongin, or a
combination of the two
Class Sclerospongiae
![Picture](/uploads/1/1/5/0/11508385/6923055.jpg?401)
This is the smallest class of Porifera, which have skeletons that
contain all three kinds of material: calcium carbonate, silica, and
spongin.
contain all three kinds of material: calcium carbonate, silica, and
spongin.