Abstract
The various biometrical criteria used in the study of the population structure of the annelid polychaete Nereis virens (Sars) are reviewed. This type of study, which requires the examination of large numbers of specimens representing all size classes, is sometimes complicated by the occurrence of autotomy, a phenomenon quite frequent in this species, and by mechanical breaks during sampling and sieving. Measurements such as total length, width of an anterior segment, and total weight are not good criteria. We have used a new biometrical criterium developed at the Laboratoire maritime de Dinard (France). This criterium is based on a partial weight of animals that have been put in formaldehyde and wiped; the weight is determined from an histogram in which breaking points are "ranked". This ponderal measurement has been compared with the linear measurement of the jaw length. The new method allows the manipulation of a larger number of individuals and it is easier and faster to use than the method based on jaw measurements.[Journal translation]
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