The shell and internal anatomy of the montacutid bivalve Mysella verrilli is described for the first time. The species is remarkable in that the oesophagus has developed into a suctorial proboscis. This has been accompanied by the loss of the palps. In addition the gonads have been extended from the dorsal part of the body to form two gill-like extensions to which the reduced inner demibranchs attach along the postero–ventral margin. Mysella verrilli broods its young in the mantle cavity to the late veliger stage before releasing them. It is believed that the species is probably a suctorial ectoparasite on a soft-bodied benthic invertebrate.