Deep sea glass sponge
The sea sponge occupies a niche position in taxonomy – not quite an animal but also not a fungus or plant – and the glass sponge could be the weirdest of them all.
Sponges are considered the most simple of multicellular animals, and have physically changed very little over the 800 million years they’re estimated to have existed, according to Chris Battershill of the Australian Institute of Marine Science in Townsville, Queensland. But, “they have evolved a very clever biochemistry such that they can produce some of the most complex and medicinally potent molecules discovered,” he says.
These compounds, including powerful neurotoxins and anti-cancer agents, are likely used to deter would-be predators or protect themselves from infection. And the pharmaceutical potential of the sea sponge has captured researchers’ attention. Battershill says that an understanding of how these animals feed may even yield new biotechnologies for food industries.
Of all the sea sponges, the relatively uncommon glass sponge (class Hexactinellid) could be the weirdest of them all. Made up of a network of small spicules covered by a thin layer of living cells, glass sponges are heavily defended both inside and out.
They occur most frequently in the deep sea and resemble delicate vases more than they do living animals. Their rising stalks provide structure to an otherwise flat habitat, and allow a variety of fish and invertebrates to anchor themselves above the seafloor where ocean currents deliver more nutrients.
Spongicolid shrimp take the habitat provisioning of the glass sponges even further. Upon encountering a glass sponge (genus Euplectella), a pair of microscopic larvae will enter through the small pores in the lattice of spicules. One will develop into a female and the other into a male, and as they grow larger than the lattice pores, their glasshouse will become a glass prison. The couple will spend the rest of their lives in the sponge, mating and releasing larvae that will exit through small pores to find their own glasshouses.
Recently, hexactinellids have become the focus of technological research. Glass sponge spicules, made of silicon dioxide (like sand and glass), have excellent strength, flexibility and optical transmission properties, and can grow over two metres long in some species. Researchers are investigating their application to fibre optics and materials engineering.
Battershill says that by finding out how glass sponges manufacture these components and their spicules, “we will learn how to construct and design silicious nanoparticles with intricate detail for novel applications as biomaterials for industry.”
Despite their ecological and technological importance, glass sponges remain a mystery. Their mode of reproduction, feeding and habitat preferences are unknown for many species. But there is little doubt that these simple glass animals hold amazing and complex possibilities.