Fossils of Virginia       Click the physiographic map to the
right for fossils in other parts of Virginia  Virginia geologic
cross-section Appalachian Plateau Appalachian Plateau Valley and
Ridge Blue Ridge Piedmont Coastal Plain Coastal Plain Coastal
Plain Untitled Document Untitled Document Balanus concavus
'Acorn barnacle' Calvert, Eastover, Yorktown, and Tabb
Formations; Present  Untitled Document  Barnacles are sessile
crustaceans, which means they do not move around. Larvae are
free-swimming for a short time, and then they attach their heads
to a hard surface (shell, log, or rock). They then build a
protective shell around themselves out of calcite, a mineral
composed of calcium carbonate. Barnacles feed when covered by
water by extending feathery legs to trap food particles, and can
close off their shell entirely when water levels drop during low
tide. They retain sufficent moisture inside the shell to last
until water covers them again at high tide. This adaptation
allows barnacles to live successfull