Amphioxus, Lancelet

The lancelet Branchiostoma lanceolatum is considered an invertebrate although the species bears quite some resemblance with ‘primitive fish’. It is possible to distinguish a head with a mouth surrounded by fine tentacles (used to gather food), a ‘body and a ‘tail’. The animal is covered with fins and manages to cover small distances by swimming; however, the lancelet is buried in coarse sediment most of the time.

In the 1976-1986 period Branchiostoma lanceolatum was widely spread outside the near-coastal zone and reached densities of 600 ind./m2 maximally in that area. In the 1994-2001 period the distribution of the species was remarkably more limited and lower densities were observed: B. lanceolatum was exclusively found near the Hinder Banks in densities of maximum 120 ind./m2.

Branchiostoma lanceolatum clearly prefers coarse sediments: the relative occurrence in sediments with a median grain size of 600-650 µm amounts to 20%. The mud content of the sediment is always less than 10%.