六放海绵纲为多孔动物门的一个纲。该纲动物具有硅质骨针，有些骨针能聚合成网状的骨架。骨骼中无海绵质。本纲又称为玻璃海绵。六放海绵纲动物大多数生活在200～8500米的海底。

六放海绵纲分为两个亚纲：

• 六放海绵亚纲
• 双盘海绵亚纲

Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma.