Published online by Cambridge University Press: 11 May 2009
The digenetic trematode Proctoeces subtenuis (Linton, 1907) is recorded from the kidney of the lamellibranch Scrobicularia plana (da Costa). At Chalkwell in Essex all of nearly a thousand S. plana examined were found to be infected, as were three of approximately 150 S. plana at Whitstable in Kent. The average number of parasites per host was between four and five. No Proctoeces subtenuis were found in Scrobicularia plana examined from other localities in Essex, Devon, Wales and Suffolk. The environmental conditions of a parasite in the lamellibranch kidney are discussed. It was found that the kidney fluid surrounding the parasites varies in osmotic pressure.
The anatomy of the parasite is described. The excretory bladder has a cellular wall, thus disagreeing with the inclusion of Proctoeces subtenuis in La Rue's superorder Anepitheliocystidia. The red colour of the parasite is due to a native haem pigment. The egg capsules are hardened by a quinone-tanning mechanism, but incubation with catechol, protocatechuic acid, and dopa failed to reveal the presence of a phenol-oxidase.
The species of Proctoeces are reviewed, and some revisions suggested. P. magnorus Manter, 1940 is considered a synonym of P. subtenuis, and the synonymy of P. erythraeus Odhner, 1911 with P. subtenuis is confirmed. The differences between P. insolitus (Nicoll, 1915) and P. subtenuis, and between P. maculatus (Looss, 1901) and P. subtenuis, require re-examination. It is considered that P. macrovitellus Winter, 1954 should be excluded from the genus Proctoeces. A definitive host list of Proctoeces spp. is given.
The adult nature of P. subtenuis from Scrobicularia plana is discussed, and it is suggested that Proctoeces subtenuis in the Thames estuary shows an abbreviated life cycle restricted to invertebrate hosts.