On the Biology and Relationships of the LamellibranchXylophaga Dorsalis(Turton)

Abstract

The exhalant siphon ofXylophagais greatly reduced and its opening is situated within the burrow. Faeces accumulate in the posterior end of the burrow in a compact mass.The ctenidia and labial palps ofTeredo, BankiaandXylophagaare modified and reduced, unlike those of the Pholadidae. The ctenidia are flat and homorhabdic and possess no ciliary sorting mechanisms; they consist of the outer demibranch only.The ctenidia ofXylophagaare composed of a direct lamella; those ofTeredoandBankiaare divided into anterior and posterior portions connected by a branchial groove which is an extension of the marginal food groove of the gill. The number of filaments in the anterior portion of the gill varies according to the species, and is of assistance in identification.The labial palps ofTeredo norvegicaare least reduced; inXylophaga dorsaltsreduction is greater, though selection of food material is still exercised. The greatest reduction has occurred inTeredo megotaraand inT. navaliswhere there is no selection.The ciliated mantle tracts inTeredoand inXylophagaplay an important part in limiting the quantity of food particles passed from the ctenidia to the mouth.