Distribution: Widespread in the Caribbean and tropical Eastern Pacific; subtidal in coral rubble (also reported from mangrove root mats); very common in Bocas. Characteristics: In this subgenus the longitudinal body wall musculature is organized in bands. In A. fischeri the bands are rather indistinct and anastomosing. It has a round anal shield with indistinct borders. Trunk up to 16 mm long. Although the species of this subgenus in Bocas del Toro are relatively easily distinguished, it may in some cases be necessary to study hook morphology by compound light microscopy.