A mussel has been captured on video flapping its mantle in an attempt to lure a fish to involuntarily serve as a host for its larvae.
The short clip, which was posted online by the West Virginia Division of Natural Resources (WVDNR), shows a plain pocketbook mussel demonstrating a strange reproductive strategy.
Plain pocketbook mussels spread their young by hitching a ride on fish, and they use aggressive mimicry to entice and deceive potential larval hosts.
They possess an enlarged and specially adapted mantle that resembles a small fish, which pregnant females display externally between their valves, and twitch repeatedly.
When a predatory fish notices the lure and, mistaking it for prey, takes a bite, they unwittingly puncture the marsupia chambers that contain the mussel’s microscopic larvae, called glochidia.
This releases the glochidia, which then attach themselves to the fish’s gills or fins.
A cyst will form around each glochidium, and they will continue to live there as parasites for weeks or months, before falling away to start the next stage of their lives.
“The larvae will harmlessly attach to the fish until they transform into juvenile mussels and drop off to live in a new area,” WVDNR explained on Facebook.
According to Animal Diversity, plain pocketbook mussels predominantly target centrarchids, such as largemouth bass, smallmouth bass, green sunfish and bluegill, as suitable hosts.
“Native freshwater mussels cannot swim or crawl, so hitching a ride on fish is the only way for them to spread throughout the watershed,” WVDNR said.
“If you’re lucky enough to find a mussel displaying her lure, look but don’t touch! If something other than a fish disturbs her, she could have to wait more than a year to successfully reproduce.”
The plain pocketbook mussel isn’t the only mollusc to rely on larval hosts for reproduction. In fact all unionidae, which is the family of freshwater mussels that the plain pocketbook belongs to, spread by means of a larval host.
However, rather than a fish, the salamander mussel uses salamanders as their larval hosts, with their glochidia attaching to the amphibian’s gills.
Perhaps even more extraordinary is the behavior of the northern riffleshell. Like plain pocketbook mussels, they lure in potential larval hosts by exposing their mantle tissue, albeit as part of a less spectacular display.
When a fish comes close enough, they close their shells around it, trapping and holding it for several minutes as they release their glochidia at their leisure, before eventually setting the fish free.