Empirical evidence of planktotrophic life in Zygochlamys patagonica larvae.

SCHEJTER LAURA; BREMEC CLAUDIA; WALOSZEK DIETER

Halifax, Canada

Workshop; 16th. International Pectinid Workshop; 2007

 During 2006 sampling procedures, recently settled spat were found attached to adult scallop and hydroids during epibiosis studies. Photographs of nine specimens (482 – 2788 µm total shell height ) allowed us to make some measures in order to determine PI and P II sizes, and the PI / PII ratio. A brief description of the recently settled spat shell ornamentation is also given. Zygochlamys patagonica fits well with the planktotrophic larvae theoretical model, having a PI/PII ratio of 0,364 ± 0,025, with an average size of the P II of 242,4 µm ± 13,879 µm and an average size of the P I of 91,75µm ± 6,178 µm. Microsculpture of the pre-radial stage of Zygochlamys patagonica left valve is composed of radial and concentric riblets forming a grid. 21 primary ribs are evidenced from the biggest specimen (2,788 µm), sometimes with incipient secondary ribs between them. Primary ribs started at ~ 1,700 µm, which explained the lack of this ornamentation in the other studied spats (all of them ≤ 1,600 µm). Auricles are almost equal in size. The right valves are completely smooth, and only presented concentric growth lines. Anterior auricles of the right valves present a radial crest with protuberances.