They are usually classified in the Class Hexactinellida along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma.
Hexactinellids are relatively uncommon and are mostly found at substantial depths, although the species Oopsacas minuta has been found in shallow water. There are big differences between hexactinellids and other sponges. They are often cup-shaped animals with sturdy internal skeletons made up of fused spicules. Much of their body tissues are syncitia, extensive regions of multinucleate cytoplasm. They are fairly common relative to Demosponges as fossils, but this is thought to be, at least in part, because their spicules are sturdier than spongin and fossilize better. Unlike other sponges, they do not possess the ability to contract.
One ability they do possess is a unique system for rapidly conducting electrical impulses across their bodies, making it possible for them to respond quickly to external stimuli. Hexactinellids like "Venus' Flower Basket" have a tuft of fibres that extends outward like an inverted crown at the base of their skeleton. These fibres are between 50 and 175 mm long and about the thickness of a human hair. They work as optical fibres that are surprisingly similar to those used in modern telecommunication networks and could even be more handy than the artificial versions. The biological fibres of the sponge conduct light beautifully when they are illuminated, and use the same optical principles that modern engineers use to design industrial fibre optics.
Despite not having the ultra-high transparency needed for telecommunication networks, they do have other advantages; unlike commercial fibre, it is possible to tie them in tight knots without them cracking or breaking. Another advantage is the fact that these biological fibres are produced by chemical deposition at the temperature of seawater. For the moment, human fibre optics can only be produced with a high-temperature furnace and expensive equipment. The earliest known hexactinellids are from the earliest Cambrian or late Neoproterozoic.
These creatures also have the longest lifespans of all creatures (up to 15.000 years) according to AnAge Database.