Comportement exp�rimental de Lingula anatina (Brachiopoda: Inarticulata) dans divers substrats meubles (Baie de Mutsu, Japon)

Abstract

Lingula anatina Lamarck was collected from the vicinity of Asamushi, Japan, in May 1982. Burrowing up to the surface by this brachiopod compensates for natural sedimentation above its burrows and is essential to its survival. Its speed of ascent was measured during experiments using various soft substrates in aquaria (coarse >2 mm and fine 2 mm in situ sediment). In all experiments, L. anatina was able to move up through the sediment, but ascent speed differed between the substrates. Ascent through the in situ sediment was much faster, since the sediment layer was deeper (up to 30 cm), and was achieved without autotomy of its pedicle which can attain a length 20 times greater that of its shell. Ascent is also rapid in brachiopods without pedicles,but such individuals maintain their filtering position with difficulty and generally emerge onto the sediment surface. In coarse-grained substrate (>2 mm) lacking fine-grained particles, L. anatina moves up but is unable to construct a burrow, and finally emerges onto the sediment surface, often after complete autotomy of its pedicle. In very fine sediment (<50 μm), L. anatina is able to burrow without clogging its pallial cavity with the very fine particles, but its valves are inadequately supported by the soft burrow walls in such fluid sediment, and maintenance of its filtering position is not possible. Our results invalidate some general concepts about suspension-feeders. The role of the pedicle is limited to anchorage at the bottom of the burrow and to retraction into the burrow; in certain cases it appears to be a handicap to ascent to the sediment surface.