Among the Grant Museum’s collection of glass sponges, there are a few specimens that really demand attention. One is the Venus’ flower basket, Euplectella aspergillum, an intricate weave of spicules in the shape of a sealed cone. Its romantic name comes from the behaviour of a species of Spongicolidae shrimp who make their home inside the sponge’s glass cage, where they feed off creatures filtered through the sponge’s walls. Having entered the sponge at the larvae stage, the shrimps grow too big to ever leave and remained trapped inside for life. In parts of Japan, dried specimens of the Venus’ flower basket are given as a wedding present, with the two shrimp preserved inside.
The other show-stopping specimen is harder to see, as it sits in the dark in an out-of-reach cupboard: the glorious glass rope sponge, Hyalonema sieboldi. Formed of a bulbous top of interlocking spicules, this animal roots itself into the sea floor using a long twisting rope of glass, which resembles a bundle of optical glass fibres. The Museum’s specimen has been mounted within an unsteadily tall and thin glass jar, and visitors can only spot it up in the rafters using the binoculars provided. However, it is not alone. While it was alive, a cluster of zoanthids, colonizing creatures resembling brightly coloured miniature anemones, made their home on its ropey root. And it has one other attachment: a shark’s egg case, commonly known as a ‘mermaid’s purse’. Clearly, the glass rope sponge is an attractive settlement.
Glass rope sponge, Hyalonema sieboldi. Photo courtesy of the Natural History Museum, London