Monkeyface, Alabama heelsplitter, treethorn wartyback, elephant ear, pistolgrip. Names of mussels hunkered down in the shoals or gravel of the Cahaba River make you want to laugh out loud! How about a Warrior pigtoe? A Southern purple lilliput? Mussel fisherman named them after the color or texture of the shell. Pigtoe mussels are wide like a cloven hoof, heelsplitters are sharp underfoot, and wartybacks have bumps on the shell resembling warts. The outer shell surface may be smooth or have humps, ridges, depressions, furrows, and wings; it may be shiny, dull, or brightly colored with rays. The shape of the shell can be round, elongate, oval, or like a teardrop. Mussels are bivalves, meaning both sides of their shells look the same.
These native freshwater pearly mussels with the funny names have a beautiful inner shell called nacre or mother-of-pearl. Nacre color varies from white to purple, pink, reddish, salmon, or pale orange. Buttons were made from this pearly layer until plastics replaced them in the 1940s.
In additional to their beautiful pearly interior, these animals have an intriguing life cycle – based on mucus, disguise, and hitchhiking. Females release brood larvae called glochidia (glock-kid-ia), which are parasitic, usually with a fish as the host. The larvae must come into contact and infest the fish host upon release. They attach to the gills or fins of the fish, which form cysts of scar tissue around the larvae – a safe place for the hitchhikers’ long journey upstream. Since adult mussels stay in one place, seldom moving more than a few feet during their lifetimes, the release of the larvae has been linked to spawning runs of the host fish. Each “hitchhiker” goes to a different part of the river, dispersing the mussels over a large area.
Some female mussels simply discharge the glochidia into the water column, some in sticky webs of mucus through which hosts may swim and become infested. Some mussels discharge larvae in small packets called conglutinates, which look like fish food. Super-conglutinates, a combination of small packets, can resemble a minnow. A super-conglutinate is discharged into a hollow tube of mucus, which trails in the water current behind the mussel and may be more than a yard long. When moving erratically in the water current behind the mussel, super-conglutinates look amazingly lifelike and have been observed to elicit strikes by predatory fish.
The most fascinating are the incredible lures disguised as fish used to tempt host fish to approach the shell. The modification of the mussel’s mantle flaps can look like small fish, crayfish, or insects, depending on the species. When the host tries to bite the lure, the mussel sprays the fish gills and fins with tiny “hitchhiker” larvae.
A few Elephant-ear mussels (Elliptio crassidenscan) can be found in the Little Cahaba River, but they are very old. The hosts for their glochidia are Skipjack herring (Alosa chrysochloris) and Alabama Shad (Alosa alabamae). In a dramatic act, the mussel grabs the host fish by tempting it with a lure, clamps onto the fish with its valves (bi-valve – two pieces), and holds the head while pumping larvae into its gills. These larvae travel with the fish for several days or weeks as they metamorphose into juvenile mussel and finally leave the host and drift into the gravel or mud to anchor. The primary threats to the Elephant-ear are the dams on the river that block the migratory path of the Skipjack herring. It is also threatened by the decline in habitat conditions associated with point and nonpoint source water (such as dirty stormwater from rain) and sediment pollution.
Just for fun – check out these fantastic videos of mussels in action from Missouri State University.
Play animated GIF and 1st video of Broken Rays Mussel (L. reeveiana) waving its fish lure!
The female broken-rays mussel displays a mantle flap lure that convincingly mimics a small fish. The host fishes include smallmouth bass and rock bass. These predators attack the lure, rupturing the marsupia that lie between the mantle flap and releasing the glochidia.
Video: In the first sequence the conglutinate is still attached to the female mussel. The other two sequences show conglutinates that were found suspended in submerged vegetation. The MPEG-1 file about 2MB. You need a suitable player, such as the Windows Media Player that comes with Windows.
Look at the pictures and then play the video at bottom of the page for the Orange-nacre Mucket (L. perovalis)