The family Architectonicidae (sun dials) are marine heterobranchs that share some characteristics of the protoconch, operculum, etc. with opisthobranchs. Most have helical shells and feed on zoanthids. Species of several related families (such as Orbitestellidae, Omalogyridae and Rissoellidae) are also found in Hawaii but are seldom noticed due to their small size. Representative Hawaiian species:

Heliacus mighelsi CP: Maui, Nov. 2002

Psilaxis radiatus CP: Hekili Point, Maui; Nov. 2004

Heliacus sterkii (underside) CP: Airport Beach, Maui; Oct. 31, 2007

For more information see:   The lower heterobranch addendum on this site Kwajalein marginellids & cysticids by Scott & Jeanette Johnson