The Development and External Morphology of Pelagic Larval and Post-Larval Stages of the Bay Scallop, Aequipecten irradians concentricus Say, Reared in the Laboratory
Abstract:Bay scallops, Aequipecten irradians concentricus Say, are reared from fertilized eggs to preadults in the laboratory at 24.0 ± 1.0°C. The external morphology of veliger larval and post-larval stages are described. After ten days of pelagic life the larvae settle and crawl on the bottom before metamorphosis and attachment on the thirteenth day. The metamorphosis of scallop larvae involves: complete loss of velum; movement of mouth through 90° to an anterior and dorsal position; loss of anterior adductor muscle and the development of posterior adductor muscle; and development of gills. The larvae after metamorphosis attach to the substratum with byssus threads.
After attachment, the post-larval (dissoconch) shell rapidly grows to reach the adult form by the 29th day. During post-larval development, the gill filaments increase in number and size. The long tentacles and the eyes are developed on the mantle by the 23rd day and the 27th day respectively. The posterior adductor muscle and the heart enlarge by the 25th day. The post-larval scallops can free and reattach to the substratum and also show crawling movements when free on the bottom. The plicacations (ribs) appear on the 29th day and extend over the entire shell by the 35th day. The plicated scallops crawl on the vertical sides and attach at the level of water surface. The swimming ability in adult manner is developed in the plicated scallops. The young scallops also float on the water surface with extended foot and tentacles held by surface tension. The sequence of developmental changes and the functional morphology of larval and post-larval organs appear to have preadapted to the habits of young scallops.
Document Type: Research Article
Publication date: June 1, 1965
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