Invertebrate of Your Choice - Hexactinellid

The glass sponge, or known as the Hexactenllid, is a sponge that is classified in the phylum Porifera. Some researchers think that this sponge should have their own phylum, called the Symplasma. This class is divided into six orders, which are Amphidiscosida, Amphidiscosa, Aulocalycoida, Hexactinosa, Lychniscosa, and Lyssacinosa. The glass sponge is not like other sponges. Actually, glass sponges are uncommon because of the fact that they live 450 to 900 meters deep in the ocean. They are found in every ocean, but they are most common in the Antarctic and the north portion of the Pacific Ocean. One unique thing that these sponges have is that they contain a system for conducting electrical impulses across their body. This allows them to respond rapidly to stimuli outside their body. Another cool thing about this species is that some are capable of fusing to form coral reefs and they are not able to contract. One question that I have is, why are they not able to contract like other sponges?

http://lifestyleinterests.com/wp-content/uploads/2015/01/big-sponge-990x556.jpg

https://en.wikipedia.org/wiki/Hexactinellid