Behavioral State Score (BSS)
(modified from Adamo & Chase, 1991)

BSS 0:

Body completely withdrawn into shell, foot not attached   to substrate.

 

 BSS 3:

Body partially extended from shell,  tentacles extended to any degree.
: 
BSS 1:

Body not visibly extended 
beyond shell, but foot attached  to substrate (to any degree).

 

 BSS 4:

Body fully extended from shell.
BSS 2:

Body partially extended     from shell, tentacles unextended.

 BSS 5:

Body fully extended from shell, whole body movement (locomotion).