Abstract
Abstract A comparison of specimens of Nephtys caeca and N. longosetosa from the north east coast of England has shown that these two species can be reliably distinguished by examining:(a) the first setiger to bear mter-ramal cirri, (b) the pharyngeal papillae, and (c) the number of setigers in large specimens. Differences in parapodial morphology are also useful, though more variable. A long chaetal form of N. caeca, the var. ciliata of McIntosh (1908), has been shown to be present for only part of the year in the population at the mouth of the R. Tyne, and specimens belonging to this form were found to represent only a small part of the total size range of N. caeca. The length of the chaetae, relative to body size, shows a gradual transition from the var. ciliata condition to the condition characteristic of N. caeca non ciliata. It is suggested that this evidence indicates that the long chaetal form is a stage in the life history of N. caeca, possibly representing a pre-reproductive dispersive/migratory ...
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