Sizes of intramarsupial unionacean glochidia in Finland

Abstract

Glochidial shells of five species were measured. The glochidia of Anodonta anatina, Pseudanodonta complanata and Anodonta cygnea were the largest. The glochidia of P. complanata could be distinguished from those of A. anatina and A. cygnea by their clearly greater length in proportion to the height. Paired glochidia of A. anatina and A. cygnea, and Unio pictorum and Unio tumidus could not always be separated from each other with certainty solely by measurements. The glochidial sizes varied geographically and interannually, and, in P. complanata, sometimes also seasonally during the incubation. The glochidial sizes of A. anatina, A. cygnea and P. complanata were not dependent on the mothers' shell lengths. In those broods of P. complanata where the mean glochidial size (length x height/2) was large, the mean length/height ratio was also great.