MULTIPLE PATTERNS OF DEVELOPMENT INSTREBLOSPIO BENEDICTIWEBSTER (SPIONIDAE) FROM THREE COASTS OF NORTH AMERICA

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Abstract
S. benedicti Webster, a small tube-dwelling polychaete common in Pacific, Gulf of Mexico and Atlantic estuaries of North America, exhibits both lecithotrophic and planktotrophic modes of larval development. In lecithotrophic forms females produce few (9-50) large ova (100-200 .mu.m diameter). These develop in dorsal pouches into 9-12 setiger larvae, competent to settle at release. Females of planktotrophic forms produce large broods (100-548) of small ova (70-90 .mu.m), brood larvae in dorsal pouches or beneath dorsal branchiae, and release 3-7 setiger larvae, which bear long swimming setae and feed in the plankton for 1-5 wk before settling. Lecithotrophy is reported for S. benedicti populations on all 3 coasts of North America, planktotrophy from the Atlantic and Gulf coasts only. Reproductive differences observed in the field are maintained by laboratory cultures reared under constant (20.degree. C) conditions, although individuals from planktotropic and lecithotrophic populations are interfertile. Developmental variations observed in the field are believed to generate different patterns of dispersal, recruitment, population growth and mortality. Poicilogony, the occurrence of multiple development modes, may account for the considerable success of S. benedicti in North America.

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