Ouachita creekshell facts for kids

The Villosa arkansasensis, also known as the Ouachita creekshell, is a special kind of freshwater mussel. It is an aquatic animal, like a clam, that lives in rivers. This mussel is a bivalve mollusc, meaning it has two shells that hinge together. It belongs to the river mussel family.

You can only find the Ouachita creekshell in certain rivers and streams within the Ouachita Mountains in Arkansas. It has a unique life cycle where its tiny babies (larvae) temporarily attach to a fish.

What it Looks Like

The Ouachita creekshell can grow to about 5 centimetres (2.0 in) (2 inches) long. Its shell is thin but has strong "teeth" near the hinge, especially at the front. Sometimes, you might see a few faint lines on the back part of the shell. The outer layer of the shell is usually olive or yellowish-brown.

Males and females of this mussel look a bit different. This is called being dimorphic. Male mussels usually have a more oval shape. Female mussels are less flat from side to side. Their back end is shorter and sometimes has a small notch.

The Ouachita creekshell looks a lot like another mussel called Obovaria jacksoniana. However, their shell shapes and life cycles are different. They also use different types of host fish.

Where it Lives

The Ouachita creekshell is found in about 30 locations. These are small and medium-sized streams in the Ouachita Mountains of southwest Arkansas. It lives only in the upper parts (called headwaters) of the Ouachita River and the Saline River drainage systems. This includes rivers like the Caddo River and the Little Missouri River.

You can find these mussels buried in sand or gravel at the bottom of fast-moving parts of streams called riffles. They also live in slower-moving areas, but not in lakes.

Life Cycle and How it Eats

Ouachita creekshells are filter feeders. This means they eat tiny bits of food from the water. They position themselves with their siphons (tube-like parts) facing upstream. They usually stay buried in the sand or gravel, sometimes with their back ends sticking out. When the weather gets warmer in spring, the female mussels come closer to the surface to release their babies.

Like other freshwater mussels in the Unionidae family, the Ouachita creekshell has a complex life cycle. It includes a larval stage called a glochidium. These tiny larvae attach themselves to the gill, fin, or skin of a suitable host fish.

Scientists are still learning which fish are the main hosts for the Ouachita creekshell. Lab tests showed that the shadow bass (Ambloplites ariommus) might be the most important host. Other possible hosts include the Creole darter (Etheostoma collettei), the greenside darter (Etheostoma blennioides), and the green sunfish (Lepomis cyanellus).

The female Ouachita creekshell creates a special "lure" to attract host fish. It moves small parts on its foot, making the edge of its mantle (the soft body part inside the shell) wave. When a fish comes to investigate, it gets showered with glochidia. These glochidia have been growing inside the mother mussel's mantle cavity all winter.

The glochidia then attach to the fish's surface and form a small cyst. They feed on tiny amounts of fish tissue for several weeks. While attached, they change and grow (this is called metamorphosis). After they are developed enough, they drop off the fish and settle onto the stream bed as tiny juvenile mussels. The fish are not harmed by this process.

Status and Protection

The Ouachita creekshell is only found in Arkansas, making it an endemic species. It is classified as an S2 species. This means it is a species of special concern because it is very rare. There might be fewer than 20 places where it lives, or only a small number of mussels in a few spots. Because of this, it is in danger of disappearing.

To help protect these mussels, it's important to also manage and protect the fish they depend on. The biggest threats to both the mussels and their host fish are damage to their habitat. When streams are blocked by dams, it stops fish from moving freely. It also causes too much mud and sand to build up below the dam, which harms mussel populations. Another concern is competition from an introduced mussel species, Corbicula fluminea.