Glass Sponges

Sponges occupy an “intermediate position” in the classification of living things. They are not quite an animal but also not a fungus nor a plant.

 Although sponges are multicellular, they have no organs. They lack mouths, intestines, and respiratory and circulatory systems. They are made of two layers of cells; between the layers is a gelatinous layer, which contains amoebid cells and spicules (skeletal needles) or fibers. Glass sponges (also referred to as hexactinellids or siliceous sponges) are made of four- and/or six-pointed spicules made of silica (hence the name). 

In some genera of glass sponges, the spicules fuse to form rigid skeletons, which can be anchored in mud by ropy root tuffs (as long as 7 inches) or mats of spicules. The recent Euplectella ("Venus’s flower-basket") is an example of one of these glass sponges. It displays an interesting commensal relation with certain species of spongicolid shrimp-like creatures, closely related to lobsters and crabs. A young male and a young female shrimp enter the central cavity of the sponge, and after growth, are unable to escape. Their entire life is spent inside the sponge, where they feed on plankton brought in by water currents. 

Euplectella aspergillum, 21 cm length, western Pacific.

Glass sponges are common only in the deep sea, especially below 500 m. They can live, however, in relatively shallow waters (35 m depth) in cold waters in Antarctica.

Glass sponges have a long geologic history, ranging from the latest Precambrian and earliest Cambrian to modern day. 

Devonian glass sponge, 10 cm length, Early Paleozoic.