8. Apr, 2016

Two Swords

The razor shell, officially called Ensis Ensis  (latin for  sword sword) is a  common burrowing mollusk containing two parallel and elongated fragile valves. They open or shut by an elastic ligament.  Ensis is found at sandy beaches off the coasts of northwest Europe. Its taxonomy  is  still a matter of debate: whether it belongs to the bivalve  moluscs family of  Pharidae or Solenidae.  Related species (or synonyms) are E. directus, E. magnus, E. minor ans E. siliqua . Some of these species may differ in size and geographical location.

You can often find  empty razor shells on our beaches at low tide, the two shells often still connected with their hinges.  The adult shell  can become 10 cm in length. Most of the time  it  is hidden under sand, with its two siphons,  two parallel tubes at the upward side of the shell. One opening  is used  to take in water and  other opening to expel the water. The bottom side of the shell (its foot)  contains  a long muscle  used for  digging into the sand (see picture, upper part: c and d at left =siphon, b in midde =shell, a at right=foot) 

 At high tide the razor shell comes out from the sand and filter feeds, but at low tide it  burrows into sand for  safety. This is a reason why  they are not often seen alive.  With their gills they filter out phytoplankton  from the seawater. Like other bivalves they also collect heavy metals and other pollutants that build up  in their tissues.  The reason why  they are often used for  measuring the degree of pollution in certain areas.  A razor shell can bury  itself  rapidly in the bottom when needed, by taking a vertical position and using its ‘tail’ muscle to dig in.  see: https://www.facebook.com/staatsbosbeheerwadden/videos/1020223211366825/

At low tide, a keyhole-shaped depression in the sand is often the only visible sign that the bivalve is present (see picture, lower part)

Reference

Cosel, R. von, 2009. The razor shells of the eastern Atlantic, part 2. Pharidae II: the genus Ensis Schumacher, 1817 (Bivalvia, Solenoidea). Basteria, 73: 9-56