Tusk Shells (Scaphopoda)

The Scaphopoda, or tusk shells, are a basal form of mollusk which filter feed on detritus and foraminifera from the surface of soft sediments.  The muscular foot (1P) anchors the anterior end of the body in the sediment while the apical (narrow) end protrudes the surface.  Water is drawn into the mantle cavity, which has no gills, via the apical opening using cillia.  Food particles are sorted from sediment before a muscular contraction ejects  the water back out the same opening.  This diagram shows an adult laterally within its shell (1) and ventrally without a shell (2) where blue represents nervous tissue, red is blood vessels, green is gonad and yellow is the digestive system which is shown isolated in higher magnification (3).  Further illustrations show a detailed progression of development (4-11).