Glass sponge
This image is of a dried skeleton of a deep sea glass sponge named Eupectella aspergillum, also known artistically as Venus' flower basket. The reason why they are called 'glass' sponges is because they are made from silica, the same material that comprises glass. Sponges of this type are found in areas of cold sea where there is a high concentration of silica, between 10 and 1000 metres.[1]
So where does this silica come from? Silica enters the ocean primarily through riverine runoff. Marine organisms other than sponges also comprise of silica, such as tiny diatoms (a major group of algae) and radiolarians (a phylum of protozoa), which use it in their cell walls.[2] The silica in glass sponges is found in its spicules; small needle-like structures that make up the skeleton of a sponge.[3] Spicules in glass sponges are composed of three perpendicular rays giving them six points.[1] The form strong, complex structures, which explains why the largest one found was three metres high![4]
Photograph: By Randolph Femmer (National Biological Information Infrastructure) [Public domain], via Wikimedia Commons
[1] Natural History Museum, (2014), Eupectella aspergillum (Venus' flower basket), [online], available at: http://www.nhm.ac.uk/nature-online/species-of-the-day/collections/our-collections/euplectella-aspergillum/ Accessed 1st February 2014.
[2] Encyclopaedia Britannica, (2014), [online], available at: http://www.oxforddictionaries.com/definition/english/spicule Accessed 1st February 2014.
[3] Oxford Dictionaries, (2014), Spicule, [online], available at: http://www.oxforddictionaries.com/definition/english/spicule Accessed 1st February 2014.
[4] Wang X, Schröder H. C, Müller W. E., (2009), Giant siliceous spicules from the deep-sea glass sponge Monorhaphis chuni, Int Rev Cell Mol Biol, 273:69-115. doi: 10.1016/S1937-6448(08)01803-0.
