 Prionodesmacea have a prismatic and nacreous shell structure , separated mantle lobes , poorly developed siphons , and hinge teeth that are lacking or unspecialized . Gills range from protobranch to eulamellibranch . Teleodesmacea on the other hand have a porcelanous and partly nacreous shell structure ; Mantle lobes that are generally connected , well developed siphons , and specialized hinge teeth . In most , gills are eulamellibranch . 
