An anatomically bizarre, fluid-feeding, galeommatoidean bivalve: Draculamya porobranchiata gen. et sp. nov. (Mollusca: Bivalvia)

For the first time we propose ectoparasitism, by piercing and fluid-feeding in the Bivalvia. Draculamya porobranchiata gen. et sp. nov. is described and the anatomy reveals a number of functional adaptations related to the feeding mode. Primary among these is a puncturing organ situated at the anterior end of the byssus groove. The ctenidia are reduced to a series of ciliated pores set ventrally within a suspensory membrane and the labial palps are not present, indicating that suspension feeding cannot take place. The alimentary tract is highly modifled; the oesophageal musculature is in the form of a suction pump. The fore stomach is greatly expanded, lacking sorting ridges and is presumed to store large volumes of ingested fluid. The central cavity of the stomach is poorly defined with a small gastric shield and style sac while the openings to the digestive diverticula are wide. The ovary is situated in the mantle and foreign sperm are stored in paired ctenidial seminal receptacles. No males were found. There are left and right pericardia and their failure to fuse as in other bivalves prevent the development of a heart. Oxygenation of the blood probably occurs across the thin walls separating the mantle cavity and the proportionally very large blood sinuses.
Comparisons are made with Kurtiella tumidula (=Mysella verrilli) the only other described galeommatoid with a suctorial habit.