A CAUTIONARY TALE: RAZOR SHELLS, ACORN BARNACLES AND PALAEOECOLOGY

Abstract:  The extant, introduced razor shell Ensis americanus (Binney) is a burrowing inhabitant of sandy, shallow-water substrates off the North Sea and Wadden Sea coasts of The Netherlands and adjacent areas. Three articulated shells with broken valves, collected from the strandline at Zandvoort, Noord-Holland, in April 2006 have dense skeletozoan infestations of the barnacle Balanus crenatus Brugière on the outer and inner surfaces of all valves. Such infestations must have occurred after death of the bivalve, decomposition of the soft tissues (but not the ligament) and disinterment of the shells. Larvae of B. crenatus settle in the spring, suggesting that these infestations are perhaps less than a year old, and testifying to the post-mortem persistence of the ligament and the density of skeletozoan infestation after a geologically brief duration. Such specimens would be a palaeoecological conundrum if fossilized; however, the ligament is likely to rot before final burial and the valves break further. Fossil specimens would probably be interpreted as valves that became encrusted on their inner and outer surfaces (balanuliths) during a long post-disarticulation residence on the sea floor.