The Curtis Pearlymussel (Epioblasma curtisii) is a small freshwater mussel that is endemic to the Ozark Highlands in Southern Missouri and Northern Arkansas. Historically it was found in transitional stream segments between headwater and lowlands of the White, St. Francis, and Black river basins. They spend most of their time filter feeding while partially burrowed in gravel and sand of shallow riffles and runs. Little is known about their specific diet, but presumably they feed mostly on planktonic algae suspended in the water column. The life cycle of most North American native mussels includes a brief parasitic stage on fish while they are microscopic larvae. With respect to this life cycle, species in the genus Epioblasma are referred to as “host trappers”. Females attract the fish host by moving to the surface, gaping the shell widely and exposing the soft tissue inside the shell. In some species, a small lure located just inside the margin of the shell is waved. If a fish swims in to investigate the lure (or presumably the soft mussel tissue) as a potential food source, the female mussel clamps down on its head and releases larvae, which are inhaled by the fish. The fish is released shortly thereafter with larvae attached to the gills. The larvae transform into juvenile mussels while on the fish, and after a few days, drop off to begin their life on the bottom of the stream. While female Curtis Pearlymussel specimens have been observed on the surface of the substrate with widley gaped shells, no lure is evident. The exact fish host species used by the Curtis Pearlymussel is unknown, but it is presumed to be a darter species as with other Epioblasma species.
The range of the Curtis Pearlymussel has declined significantly since the early 1900’s. By the time it was listed as federally endangered in 1976, only two small populations were known to occur in the Little Black and Castor rivers in Missouri. Unfortunately, mussel communities in these streams experienced a catastrophic decline in the late 1980’s. As a result, the Curtis Pearlymussel has not been seen alive since 1993 when the last living specimen was observed from the Little Black River. There has been extensive surveys to look for the species since the 1980’s. Currently, the Service is working with state partners to search for any populations that might have escaped detection in the past in more remote stream reaches. Loss of habitat is the primary cause of decline for the species. Impoundments and channelization have been largely responsible for the decline of the Curtis Pearlymussel as much of the original range where this species once occurred has been impounded or channelized. The cause of its disappearance from the last two known populations is unknown.
The Curtis Pearlymussel is known to occur in transitional stream segments between headwater and lowlands. They require stable substrates composed of a mixture of gravel and sand and sometimes with scattered cobble and boulders in riffles or runs where a diversity of other freshwater mussels are concentrated. More specifically, it has been associated with stream channels with emergent aquatic plants growing along shore such as Spadderdock (Nuphar advena) and Water Willow (Justicia americana) in quiet water at the edge of swift current or in moderate current.
A natural body of running water.
Little is known about the specific diet of the Curtis Pearlymussel, but they are believed filter feeders like other freshwater mussels, using their gills to remove small particles suspended in the water column. While the diet of mussels is a subject of debate, it is believed to include organic detritus, phytoplankton, zooplankton, diatoms, and other microorganisms. The extent of selectivity exhibited by mussels feeding on each of these food groups and species within these food groups is not completely understood and is likely to vary by species. Recent evidence suggests that bacteria, and possibly fungal spores, may be an important food source. Mussels filter feed by waving microscopic cilia on their gills, water is pumped into the shell cavity through an opening at the margin of the shell (incurrent aperture), through the gills, and moved out the excurrent apeture. They are also believed to bottom feed by using cilia on their muscular foot to draw in food particles.
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