In september 1998 empty bivalve shells, often with dryed remnants of flesh, of the tellinid Abra tenuis were found on a tidal flat and in the tidemark of the outer harbour of Zeebrugge. This is probably the first 'recent' (in it's two senses) record for the Belgian coast, although finds of subfossil specimens in 'modem' coastal plain deposits prove that she must have lived here in historical times. Identification features of the species are compared with these of Scrobicularia plana in order to give a tool for easier distinguishing juveniles of the latter from A. tenuis >. Regarding its distribution along tbe continental coast of the North Sea, life occurrence in the sea area boundery S51 (after Seaward, 1990) is demonstrated and bas now to be indicated with status † = live record, post-1950 (in Seaward's atlas). Furthermore, some data from the French channel coast (Brittany), zones S17F and S55, must be amended to status † on the basis of Rullier (1959) and field-observations from Ile des Hébihens (Côte d'Émeraude; 1983) and the Grève de Goulven (Finistère Nord; 1991) (pers. comm. J.-P. Kreps). Tbe northernmost distribution limit of A. tenuis is discussed. So far the coast of Northumberland (East England) is the most likely northern border area of its appearance. Literature data from more northern find-spots: Norway, Lofoten, West-Finmark, Faeroer are considered as rather doubtful. Concerning the ecology of the species we know that the substrate she prefers is fine sand or a mixture of this with soft mud, where she lives burrowed at maximum 2-3 cm depth. Being a small shell and 'deposit feeder' A. tenuis needs the presence of fine sediment. Densities per m 2 are given according to Gibbs (1984) and Bachelet (1989). Further, A. tenuis tolerates reduced salinities and fully immersion for a long period. I presume she does not tolerate high energetic environments. One reason may be that the species is not a deep burrower and could easeIy be washed out. She most probably only lives at places where the bottom ...