This object, which I was shown recently, was found by Grant Nicoll of Nedd on the small beach at Torgawn (NC2032) in 2017. It brought to mind the phrase ‘something of a novelty’, beloved of my maternal grandmother.
This calcareous tube is 32 cm long, 2cm in diameter at the broader end and 1mm thick (picture 1). It has been rolling around on the bottom of the sea for some time, since it bears the smaller tubes of the keelworm Pomatoceros triqueter and some barnacles.
Paging through illustrations in my books on marine life, I found two possible candidates: the tubes of the free-living polychaete worm Serpula vermicularis and the burrow-linings of one of the shipworms Teredo spp., which are unusual bivalve molluscs. The relative straightness of the tube and its size fit the latter.
Shipworms were a scourge of wooden structures immersed in sea water, including wooden-hulled ships. They have specialised shells with which they bore holes in timber, digesting the cellulose in the wood with the help of an endosymbiotic bacterium Teredinibacter turnerae. Their tunnels are lined with shell-like material and can be closed at the outer end by two plates called pallets (picture 2). Although individuals are said to live for only a year, the largest can construct a burrow up to 60cm long. Therefore, since they live colonially, they can convert solid timber into something like a sponge (pictures 3 and 4).
Some eleven species of shipworm have been reported from British waters, mostly in driftwood. From its large size, this tube is almost certainly that of the Norway Shipworm Nototeredo norvegica, which has survived the complete erosion of the wood it was consuming. An excellent on-line catalogue and atlas The Marine Mollusca of West Scotland and the North Coast of Ireland, by Shelagh Smith and Julia Nunn, maps only one record from North West Scotland, at Loch Ewe in 1990. So, a very interesting find.
Christensen, J.M. and Dance, S.P., 1980. Sea Shells: Bivalves of the British and Northern European Seas. Penguin Nature Guides. See the striking pair of photographs of wood bored by shipworms and an x-ray of the damage caused in two years on pp. 110-111.
Yonge, C.M., 1949. The Sea Shore. Collins New Naturalist. There is a good account of the natural history of shipworms on pp. 180-184.
Ian M. Evans