Runcinida (= Runcinacea) includes small animals that have a gill
located between the mantle and foot at the posterior margin of the body.
They lack shells or have small, plate-like
shells concealed below the posterior edge of the mantle. They were
previously considered to be a family within Cephelaspidea but
were moved to their own order in Malaquias, et. al. (2009). One family
known from Hawaii.