Sponges build their skeletons using specialized cells that transport and assemble structural beams like construction workers — a novel way of producing a skeleton compared to other animals.

Sponge skeletons are made of rod-like silica structures called spicules that are cemented to rocks and to each other with collagen. To find out how the spicule assembly process works, Noriko Funayama at Kyoto University in Japan and her colleagues studied a freshwater sponge (Ephydatia fluviatilis) under a microscope and discovered 'transport cells' that move spicules inside the sponge. The cells then push the spicules through the animals' outer surface to raise them up and attach them together.

This process allows sponges to adopt a huge variety of shapes and sizes, the authors say.

Curr. Biol. http://doi.org/7sr (2015)