Dwarfism in a sabellid polychaete, a study of an interstitial species

The anatomy and behavior of a species of the sabellid polychaete subfamily Fabricinae, is described. Mature individuals are virtually microscopic and represent the extreme degree of dwarfism apparently possible for a sabellid. Eggs are matured and liberated unilaterally, one at a time, from a single thoracic segment. Dwarfism in this species is essentially a cessation of body growth at a juvenile stage, accompanied by precocious sexual maturity, as an adaptation to persistent occupation of an interstitial detrital habitat.