Venus' flower basket

Meet a relative you would never pick as family. Venus' flower basket is a true animal, a distant relative of jellyfish and corals and of two-sided animals. It is a deep-sea sponge with a lace skeleton of glass, yet it has no brain, nerves, muscles, gut or eyes. It lives fixed to the deep, dark seafloor, drawing in seawater and filtering out tiny bits of food.

Its body is a thin-walled curved tube of lace, usually about as long as a school ruler. The wall is built around glass, a square mesh with diagonal threads, only a few millimetres thick. The top has a wide opening covered by a fine sieve. The base narrows to a fluffy beard of glass hairs that anchor it on rock or in mud. It builds all this glass from seawater in the cold deep sea, with no furnace heat.

Inside many baskets lives a pair of small shrimp, one male and one female. They swim in young for shelter, then grow too large to leave. They help keep the sponge clean while they feed on scraps the sponge releases. In Japan, dried baskets with the pair still inside were given as wedding gifts, a sign of staying together for life.