Balanus crenatus

The oval shaped dome with a slit down the middle characterizes the juvenile barnacle.  The aperture (middle slit opening) is easily visible and the body of the organism can be seen inside.  The back and forth movements of the organism within its shell are apparent under a dissecting microscope.  Barnacles seem to prefer roughened surfaces.  Multiple barnacles settled in the corners of the petri dishes (where they were not photographed) and this one settled near a small crack in the plate (visible as the curved line running through the photographs).  Small spines can be seen around the edge of the shell.  As the juvenile grows older, its shell will differentiate into multiple plates, which can be used for identification.  

Anatomy of Balanus crenatus

Aperture- a ventral, slit-like opening in the shell
Capitulum- the body of the organism enclosed by a shell
Eye spots- remnants of the compound eyes of the larval stage of the barnacle

Adult morphology of Balanus crenatus