in
Lampsilis fasciola Unionidae are distinguished by a unique and complex lifecycle. Most unionids are of separate sex, although some species, such as
Elliptio complanata, are known to be
hermaphroditic. The sperm is ejected from the
mantle cavity through the male's excurrent aperture and taken into the female's mantle cavity through the incurrent aperture. Fertilised eggs move from the gonads to the gills (
marsupia) where they further ripen and metamorph into
glochidia, the first larval stage. Mature glochidia are released by the female and then attach to the
gills, fins, or skin of a host
fish. A cyst is quickly formed around the glochidia, and they stay on the fish for several weeks or months before they fall off as
juvenile mussels, which then bury themselves in the sediment. Some of the species in the Unionidae, notably in the
Lampsilini tribe, have evolved a remarkable reproductive strategy. The edge of the female's body that protrudes from the valves of the shell develops into an imitation of a small fish complete with markings and false eyes. This decoy moves in the current and attracts the attention of real fish. Some fish see the decoy as prey, while others see a
conspecific, i.e. a member of their own species. Whatever they see, they approach for a closer look and the mussel releases huge numbers of larvae from her gills, dousing the inquisitive fish with her tiny, parasitic young. These glochidial larvae are drawn into the fish's gills, where they attach and trigger a tissue response that forms a small
cyst in which the young mussel resides. It feeds by breaking down and digesting the tissue of the fish within the cyst. Sex is determined by a region located on the mitochondrial DNA, the male
open reading frame (M-ORF) and female open-reading frame (F-ORF). Hermaphroditic mussels lack these regions and contain a female-like open-reading frame dubbed hermaphroditic open-reading frame (H-ORF). In many mussels, the hermaphroditic state is ancestral and the male sex evolved later. This region of the mitochondria also may be responsible for the evolution of doubly uniparental inheritance seen in freshwater mussels. ==Taxonomy==