OutdoorNebraska

58 Pimpleback, Amphinaias pustulosa Description: The Pimpleback is a medium-sized shell (80mm) that is mostly round with a squared off posterior margin. In Nebraska the shell is moderately inflated and usually smooth though individuals with pustules have been found. They are a light yellowish tan and some, especially young ones, have a bright green stripe. There is a vague hint of a sulcus ahead of a gently rounded posterior ridge. The pseudocardinal teeth are fairly large while the lateral teeth are short and straight. The beaks are slightly raised above the dorsal margin. Beak sculpture, if any, is a couple of ridges. Similar species: The Mapleleaf and Pimpleback are often found together and are quite similar. The Mapleleaf tends to be more squarish, has a deeper sulcus, has rows of pustules on both sides of the sulcus and is a bit more compressed. The Pimpleback is rounder, has a barely visible sulcus, is more inflated and seldom has pustules. If pustules are present, they tend to run right down the middle of the sulcus. Young Pimplebacks have a single broad green stripe down the middle of the sulcus which is sometimes visible in adults. Conservation status: G5, N5, S2. While live Pimplebacks have been found in four watersheds, they are most common in the West Fork Big Blue River. A catastrophic event here could wipe out the single best population Hosts: Black bullhead, brown bullhead, channel catfish, flathead catfish, shovelnose sturgeon, white crappie. Habitats used: Medium to large rivers in mud, sand or gravel (Cummings and Mayer 1992). Small streams to large rivers on most any stream bottom except shifting sand (Oesch 1995). Large reservoirs, small to medium rivers, on gravel, sand, and silt (Parmalee and Bogan 1998). Moving water in muddy sand and cobble in large creeks and rivers (Watters et.al. 2009). Native range: Pretty much the entire Mississippi River basin as far north as North Dakota and Minnesota. Nebraska collection notes: Relict and dead shell are particularly common in the Big Blue River basin. Also found in the Nemaha, Lower Platte, and Elkhorn River basins. Live pimplebacks have been found in Walnut Creek (Nemaha basin), West Fork Big Blue and Lincoln Creek (Big Blue basin), and North Fork Elkhorn (Elkhorn basin). Archeologically, this species has also been found in the Republican basin. Comments: The Pimpleback was so named because, in most of its range, the shells are covered in pimples. However, in Nebraska, Pimplebacks with pimples are rare.

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