Usually solitary or in loose ribbons. Cells can be found with or without pili on the valve. A. mammifer pili will be crossing on the valve. A. cornucervis pili do not cross and makes it easier to identify. Distribution is in temperate waters to subtropical waters. See Tomas in Taxonomic References.
This photo was taken by Walt Butler of MANTA, Maryland Dept. of Natural Resources. He has found it in samples from Tangier Sound, Fishing Bay, and the Wicomico and Nanticoke Rivers in the southern end of the Eastern Shore of the Chesapeake Bay.