Uncinial patterns and age determination in terebellid polychaetes

This work seeks morphological criteria for estimating age and hence for demographic population studies. Observations on 6 species of terebellid polychaetes revealed a continuous formation of uncinial plates throughout the individual's life. As the replacement proceeds, the size of uncinial plates increases and the torus bears larger and larger uncinial plates between the area where they appear and where they are shed. The rate of size increase is not constant: it is pronounced in young stages but progressively slows with age. Consequently, difference in size between uncinial plates of both extremes of a particular torus varies during the polychaete's life span. Uncinial distribution along the thoraxshows the effect of change from a single to a double row. There is either retention of the same number of uncini (Neoleprea), doubling of the number (Lanice) or a middle increase (Eupolymn~a).