A discrete but protracted breeding season, extending from October to April, was defined for Lingula anatina from Townsville, Australia, using gonad indices, sizes of developing ova, occurrence of planktonic larvae and analysis of size frequency distribution of an adult population. Comparison of temperate and tropical records suggests that the duration of the breeding season is regulated by temperature. The minimum age at which larvae achieve competence to settle is approximately the same in temperate and tropical waters, but in both regions development and growth occur at a very variable rate. A number of morphological features which can be considered precursors to settlement are closely associated in their development, which may proceed in response to settlement cues provided by proximity to the substratum. The varying intensity of such cues in different environments may be responsible for delays before some larvae realize competence to settle, accounting for much of the variability in the development process. Accordingly, differences between collections of Indo-West Pacific Lingula larvae can be rationalized; all records are now referred to L. anatina. Extension of pelagic larval life in lingulid larvae appears to involve a strategy different from that of most other marine invertebrates.