The shells are long, narrow, and parallel-sided. This shape resembles a closed, old-fashioned straight razor (a cut-throat razor), or a closed jackknife (pocket knife) and sometimes these clams are known as razor shells or jackknives. The shells in these species are fragile and can easily be damaged when digging for these clams.
Ensis species live in clean sand on exposed beaches. They are capable of digging very rapidly; see the description under the Atlantic jackknife clam. Some clammers catch jackknives by pouring salt on the characteristic keyhole-shaped breathing holes. The clam then tries to escape the salt by coming up out of its hole, and at this point it is possible to gently grab the shell and pull it out of the ground.
Thirteen species are currently recognised:
- Ensis arcuatus (Jeffreys, 1865) – razor shell
- Ensis californicus Dall, 1899
- Ensis directus (Conrad, 1843) – Atlantic jackknife clam
- Ensis ensis (Linnaeus, 1758)
- Ensis goreensis (Clessin, 1888)
- Ensis macha (Molina, 1782)
- Ensis magnus Schumacher, 1817
- Ensis megistus Pilsbry & McGinty, 1943
- Ensis minor (Chenu, 1843) – jackknife clam
- Ensis myrae Berry, 1954
- Ensis nitidus (Clessin, 1888)
- Ensis siliqua (Linnaeus, 1758) – pod razor
- Ensis tropicalis Hertlein & Strong, 1955
- S. Gofas (2010). "Ensis Schumacher, 1817". In P. Bouchet, S. Gofas & G. Rosenberg. World Marine Mollusca database. World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=138333. Retrieved April 26, 2010.