Invertebrates
Venus's Flower Basket
Euplectella aspergillum · also called venus flower basket, venus's flower basket, glass sponge
Venus’s flower basket is a deep-sea sponge that builds itself a home out of glass. Its skeleton is a fused lattice of silica — the same stuff as window panes and optical fibre — woven into a slender, curved tube so regular and so strong for its weight that engineers study its geometry. And more often than not, a pair of shrimp lives sealed inside it, unable to leave, for the rest of their lives.
Overview
Venus’s flower basket grows on the soft sediment of the deep seafloor in the western Pacific, especially around the Philippines and Japan, usually hundreds of metres down in cold, still, food-poor water. The glassy tube is typically 10–30 cm long, thin-walled, open at the top, and anchored to the bottom by a tuft of fine glass fibres.
A skeleton of glass
Special cells pull dissolved silica from seawater and lay it down as tiny spicules, which in this sponge are fused and cross-braced into one rigid framework. The openings sit in a strikingly regular grid, reinforced along the diagonals — a structure that is mostly empty space yet resists bending far better than its weight suggests. The anchoring fibres also carry light along their length, much like manufactured optical fibre.
The shrimp within
A male and a female shrimp usually enter the sponge as tiny larvae, then grow too large to escape through the lattice. The pair lives out its life inside, breeding, with only their minute offspring small enough to slip back out. In Japan the sponge has been given to newlyweds as a symbol of a bond that lasts until death.
How it feeds
Like all sponges, it has no organs or nervous system. Countless microscopic flagellated chambers beat in unison to draw seawater slowly through the body wall, straining out bacteria and fine organic particles.
Status
The species has not been formally assessed. It is known from scattered deep-water sites, where bottom trawling and seabed disturbance are the main threats to glass sponge grounds.
Venus's Flower Basket: common questions
Is Venus's flower basket a single animal or a colony?
It is a single animal, a sponge, though sponges are so unlike familiar animals that the question is reasonable. A sponge has no organs, no nervous system, no muscles, and no true tissues in the usual sense. Instead it is a coordinated community of cells that together pump water through a body wall riddled with channels, filtering out food as they go. Venus's flower basket is one individual of the glass sponge group, and what we usually see, the beautiful latticed tube, is the mineral skeleton that its living cells built and lived within. When the sponge dies, that glass skeleton can persist on the seabed or be collected intact.
How does a sponge build a skeleton out of glass?
Specialised cells take dissolved silica out of seawater and lay it down around a protein thread to form spicules, tiny glass rods and stars. In most sponges the spicules stay loose or lightly bound, but in Venus's flower basket they are cemented and welded together into a single rigid framework, with the openings arranged in a strikingly regular grid and reinforced along the diagonals. The result is a structure that is mostly empty space yet resists bending and buckling remarkably well for its weight, which is why materials engineers have analysed its geometry as a model for lightweight construction.
What is the story of the shrimp inside?
Small shrimp of the genus Spongicola, usually a male and a female, enter the sponge's central cavity while they are still tiny larvae. Inside they are safe from predators and bathed in the steady current of food-bearing water the sponge pumps. But as they grow, they become too big to squeeze back out through the glass lattice, so the pair is effectively imprisoned together for the rest of their lives. They breed within the sponge, and only their minute young can pass out through the mesh to find sponges of their own. This lifelong confinement of a shrimp couple is the source of the sponge's use as a wedding gift in Japan.
Why is it called Venus's flower basket?
The name is old and admiring. The delicate, white, woven appearance of the glass skeleton reminded nineteenth-century naturalists and collectors of a finely made basket, and attaching the name of Venus, the Roman goddess of love and beauty, marked it as something especially lovely, an association reinforced later by the romantic tale of the shrimp pair within. Dried skeletons became prized curiosities in Victorian collections and remain popular museum specimens today, valued both for their beauty and as an example of biological engineering.