PERNET, B.; California State University, Long Beach: Feeding by larvae of two different developmental modes in the annelid Streblospio benedicti

Females of the spionid polychaete Streblospio benedicti produce either small eggs that develop into planktotrophic larvae, or large eggs that reportedly develop into nonfeeding, lecithotrophic larvae. This apparent polymorphism is potentially useful for testing hypotheses on the ecology and evolution of maternal investment and larval development, but critical basic information on the morphology and functional biology of both types of larvae are lacking. Here I report on the nutritional biology of larvae of S. benedicti. Immediately after release from the maternal brood pouch, both types of larvae were able to use opposed bands of cilia to capture suspended food particles and transport them to the mouth. This particle capture mechanism has not previously been reported from spionids. In laboratory cultures, both planktotrophic and lecithotrophic larvae regularly ingested captured particles. Laboratory experiments showed that lecithotrophic larvae reared with suspended food grew more rapidly than did sibling larvae reared without food, indicating that these larvae can also digest and assimilate ingested food. Larvae of S. benedicti that develop from large eggs are best regarded as facultative planktotrophs rather than obligately nonfeeding lecithotrophs, a result that has important consequences for the interpretation of comparative studies of the ecology and evolution of maternal investment and larval form in Streblospio.