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Description:
The incongruous ark grows to approximately 2.5 inches.  It is typically white to gray in color, with shells being heavy and strongly ribbed.  There are 26-28 radial ribs, square in cross-section, with bar-like transverse beads.  The left valve overlaps the right valve considerably.  The shell is covered in a thin, brown periostracum.

Habitat:
Sandy subtidal zone to offshore coastal waters.  Also occurs in seagrass beds.

Similar Species:
Several members of this genus inhabit the IRL, but they may be easily distinguished.  The eared ark, Anadara notabilis grows to 3.5 inches and has prominent concentric markings on and between the radial ribs.  The blood ark, Anadara ovalis, is generally the same size as the incongruous ark, but has up to 35 radial ribs.   The transverse ark, Anadara transversa, is the smallest of the Atlantic arks, growing only to 1.5 inches, with 30-35 radial ribs. 

Range:
Incongruous arks may be found from North Carolina south to Brazil, including the west coast of Florida and the Texas coast.  The are fairly common throughout the Indian River Lagoon, especially around inlet areas. 

Anadara brasiliana, the incongruous ark, from the Indian River Lagoon.  The pattern of transverse beading on the radial ribs is visible in the upper right.   Photo courtesy of K. Hill, Smithsonian Marine Station.