More like centipedes that came in from the deep than mere worms, polychaetes have made the most out of a simple structure of repeated segments, each armed with biramous setae or bristles that help many species plough through the silt or a deliver a short, sharp lesson in pain management. Many families, however, have shunned a life of abandon for the security of burrows or tubes, creating the latter out of sandy grains or by secreting a protein that coagulates into a funnel resembling parchment or silk.
Onuphid worms in the genus Diopatra are among the most prominent yet elusive tube dwellers on local mudflats and unconsolidated beaches. The worms stick leaves, shells, algae and other debris to camouflage their hide, strengthen its walls and supplement their usual diet of hapless creatures or plants that stray too near the lair. The animals will leave their retreats to forage or flee diminishing returns, revealing a body lined by well-developed parapodia and a head region bearing grasping appendages and long sensory palps.
Other onuphids construct temporary dens or take the tube wherever they go, like marine caddisflies that never grow up. One probable representative of this group was barely evident as it crept about in a tidepool at Sembawang, where a broad strand of crumbly sand has formed near the mouth of a creek towards the eastern end. Feeding among fragments from nearby woods in pockets of still water were minute sea anemones, hermit crabs and even tinier worms. Secure in its tubular armour, the polychaete extended its cephalothoraicic segments to probe its surroundings before inching its way onward to fresh patches. Flashes of harsh light caused the worm to scoot back into its stiff but supple home, which is as neatly rolled as a homemade joint and has plenty of wriggle room for its inhabitant to slide lengthwise. For builders of both modest shelters as well as postmodern subways, it probably pays to ditch the bottom-line for systems with space to spare for growing scales and the means to buy time without breaking down.