ARCIDAE (Ark Cockles)

Seashells

Anadara trapezia (Mud Ark, Ark Cockle)

Ark cockles (Ark Shells) are both marine and estuarine, preferring estuarine tidal flats and seagrass beds. They range from Fraser Island on the southern Queensland coastline, southward through southern coastal waters. They grow to about 7cm and have thick, oblique shells with predominant ridges. Also known as Mangrove Cockles. It has been used as a bioindicator/indicator species to study levels of the metals selenium, copper and cadmium.

Ark clams are easily recognizable by their distinct ark-shape, and clear muscle scars on the inside. Generally white, brown, or tan shades on the outside, they tend to have whitish insides.

Ark shells frequently have a byssus by which they attach themselves to rocks or other substrata.

In Ark Shells the pigments hemoglobin and myoglobin are found dissolved in both the blood and tissues, coloring the muscle red (not typical of bivalves, which generally absorb oxygen from water into the tissues directly, without the aid of oxygen transport pigments). Where the water is very muddy, oxygen may be deficient, in which case these pigments facilitate oxygen transport into the tissue.

Photo: Robert Whyte