The Hexactinellida are commonly known as the glass sponges and include the Venus' flower basket (Euplectella spp.) which can be seen below, and Regardrella okinoseana, a lacy basket sponge below. They are often radially symmetrical and vase- or funnel-shaped and can be up to 1 m across and 1 m high, and are very beautiful. Their distinguishing feature is the network formed by the six-rayed siliceous spicules. There are about 500 species. They occur mainly in deep, cold waters between 200 - 2000 m, although some can be found below 6000.
Euplectella sp. is rather atypical as it is found in tropical waters at around 150 m, and is rarely taller than 30 cm. Some species of Euplectella have a commensal relationship with a shrimp, Spongicola venusta. A young male and female shrimp enter the central cavity and live there. As they grow they become too large to escape through the sieve-like covering of the osculum, and so spend their entire life inside the sponge. Synconoid and leuconoid canal systems occur in this class.
The Glass rope sponge, Hyalonema sp. above is found worldwide in deep waters. It ranges in length from 18 - 50 cm - most of this being the stem. The body averages 5 - 8 cm long with a diameter of 3 - 6 cm. The long stalk of the sponge anchors in soft sediments on the sea floor.
Hyalonema sieboldi, below, shows where the "glass rope" of the common name comes from. This sponge is found off the coast of Japan.