Planktonic larvae ofSpiochaetopterusin the Gulf of California: New evidence that the geographic distribution of species with a long planktonic larval life is relatively restricted

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Abstract
Polychaete larvae were sorted from a collection of 116 zooplankton samples taken in 76 localities during the GOLCA 84-04 cruise in March-April 1984. Two morphologies were identified in the Chaetopteridae genus Spiochaetoplerus: larval types I and II. The morphology of A4 setae dissected from the larvae is compared with A4 setae of erected species from the Pacific. Larvae of Spio-chaetopterus type I could belong to S. monroi. From local observation of adults and larvae, and comparison with the first species described in the genus: S. costarum, it appears that this species is not present in the Gulf of California. Although S. costarum was for a long time credited with a widespread distribution throughout the world because of its long planktonic larval development, it is now acknowledged that many reported occurrences were incorrectly attributed to S. costarum, and in consequence its specific area has been restricted in recent years. This paper confirms that the setal morphology of larvae and adults is very helpful in the identification of planktonic larval stages.