Poecilogony, defined as more than one mode of reproduction within a single species, has been reported in various invertebrates, including mollusks and polychaetes. Many cases that have been described involve planktotrophic and non-planktotrophic development in allopatric populations, or instances of planktonic larval stages and benthic juveniles being found together, but not associated with adults. There is always the possibility of mis-assignment of larvae to adults of the wrong species. Most cases that offer these kinds of evidence are now known to involve cryptic species, not poecilogony.

There are a few species in which release of young occurs both at metamorphosis and a day or so before. There may be cases in which extracellular yolk or nurse-egg production is variable and allows the release of larvae at different stages, but no actual instance is known. A few instances are known of allopatric populations with different modes of development and other differences in reproductive characters that lack reproductive isolation when brought into the laboratory. The polychaetes Streblospio benedicti, Cirriformia tentaculata, Boccardia proboscidea, and the opisthobranch Elysia chlorotica are in this category. All examples of poecilogony require further genetic substantiation.

Despite the scarcity of proven examples of poecilogony, the presence of more than one mode of reproduction within a genus is the rule in most invertebrate phyla. The evolutionary and ecological significance of these patterns is discussed.