Glass sponges, or sponges in Class Hexactinellida, are a unique group of deep-sea sponges that provide a window into the evolution of sensory systems. Instead of having individual cell types, glass sponges are syncytial (pronounced sin-SISH-el) with one giant cells and nuclei that migrate around along long trackways throughout the sponge. Syncytial tissues generally allow communication between regions of an embryo or, for example, muscle. Syncytia allow action potentials to travel across the sponge body and these cause flagella arrest, stopping the filtration of water. Why glass sponges alone among Porifera have electrical signalling is one of our group's areas of study. The route to answering this question is a little circuitous, but may lie in the low food habitat of the deep sea.
Glass sponges also hold our interest because of the unique habitats they created up until the Cretaceous Period. Today, glass sponge reefs are present in the shelf waters of Western Canada and the USA and have been found to serve important ecosystem functions as habitat for other animals and through local silica and carbon cycling.