10.1016/s0967-0653(97)83031-1

Poecilogony is a polymorphism of sexual development in some marine invertebrates, in which both feeding and non-feeding or planktonic and benthic larvae are produced. Since the original report on poecilogony by Gaird in 1905, a good number of such species have been recognized. Upon close examination, however, Hoagland and Roberston (1988) have found that almost all the 64 species reported to be poecilogonous are in fact a result of miss-identification of species or due to laboratory disturbance. To be a poecilogonous species, a different mode of development has to be found from sibling offspring of a single female, or from different individuals of a single biological species, and the different modes of development cannot be altered by disturbance in laboratory handling. This being the case, there are only a few known species which are poecilogonous. As a reproductive strategy poecilogony appears to have the advantages of both the commonly recognized patterns of development, short planktonic or benthic development (without planktonic larvae) and long planktonic development (broadcaster, with planktonic larvae). The former allows immediate recruitment to the parental habitats for fast population growth and the latter provides some degree of dispersal and gene flow. In this paper, we briefly review the reproduction and larval development of three poecilogonous species (Haminaea callidegenita, Streblospio benedicti and Capitella sp.) and pose the following questions: 1) Why are the currently known examples of poecilogonous species found only in polychaetes and opisthobranchs? 2) Why are poecilogonous animals predominately located on mud flats? 3) If poecilogony is such a good reproductive strategy, why don't we see it in more species? We reasoned that polychaetes and opisthobranchs may be genetically predisposed for more flexible reproduction, and that the mud flat is among the most dynamic marine habitat, exerting greater selective pressure favoring polymorphism of reproduction than that of other habitats. We reasoned also that there may be more such species which can only be discovered through intensive and long term research on the reproductive biology of invertebrates on mud flats.