Overview

Brief Summary

Biology

The unclosed side is turned up when burrowed into the substrate, mostly sand or muddy sand, in which it forms a hole. Goes up and down into the substrate with a respectable speed (disappears into sand within 15 seconds).
  • Leewis, R. (2002). Flora en fauna van de zee [Marine flora and fauna]. Veldgids, 16. KNNV Uitgeverij: Utrecht, The Netherlands. ISBN 90-5011-153-X. 320 pp.
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Distribution

A recent immigrant from America, this species is now very common along the European coasts. First discovered on German North Sea Coasts in 1979, it had reached NE Denmark and the Dutch Wadden Sea by 1982, and NE France by 1991.
  • Hayward, P.J.; Nelson-Smith, A.; Shields, C. (1996). Collins pocket guide: sea shore of Britain and Europe. Collins pocket guides. Harper-Collins Publishers: London, UK. ISBN 0-00-219955-6. 352 pp.
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Labrador to Florida
  • North-West Atlantic Ocean species (NWARMS)
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Geographic Range

Ensis directus is found along the Atlantic coast from Canada to South Carolina. It lives in the intertidal zone or subtidal zone in the sand or muddy bottoms.

(Jobin and Jobin 1997, Gosner 1978)

Biogeographic Regions: atlantic ocean (Native )

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Physical Description

Morphology

Physical Description

Ensis directus has a thin, elongated shell that is slightly curved. It ranges from yellowish to dark brown in color. The length of E. directus is about six times its width. It can grow to be about 10 in. It has a coating around its shell to protect it from eroding in the mud or sand. Ensis directus is a bivalve, which means that its shell has two parts. The body of Ensis directus is surrounded by the mantle and the mantle is seperated into two parts. Each part of the mantle secretes a shell. The two shells are connected by an elastic ligament that allows for it to open and close. Both parts are usually identical and are made up of calcium carbonate and protein. It has a huge foot that allows it to move through water or to burrow in the sand. When the foot is extended all the way, it is almost as long as the clam's body.

(Alexander 1979; Lippson 1984)

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Diagnostic Description

Morphology

Whitish-grey mollusc with brown drawings. Length six times as wide, slightly curved, and can attain at least 20 cm long. Both tips equally wide.With many growing bands and a scaly surface. As with all Ensis spp. one side is never completely closed.
  • Leewis, R. (2002). Flora en fauna van de zee [Marine flora and fauna]. Veldgids, 16. KNNV Uitgeverij: Utrecht, The Netherlands. ISBN 90-5011-153-X. 320 pp.
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Diagnosis

Conrad, 1843. Proc. Acad. nat. Sci. Philadelphia, 1: 325
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Ecology

Habitat

In sand or muddy sand.
  • Leewis, R. (2002). Flora en fauna van de zee [Marine flora and fauna]. Veldgids, 16. KNNV Uitgeverij: Utrecht, The Netherlands. ISBN 90-5011-153-X. 320 pp.
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infralittoral and circalittoral of the Gulf and estuary
  • North-West Atlantic Ocean species (NWARMS)
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Ensis directus lives in the sandy bottoms in the intertidal or subtidal zones along the Atlantic coast. It is usually found in colonies. It is not migratory and therefore it remains in its habitat year round.

(Gosner 1978)

Aquatic Biomes: coastal

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Depth range based on 1945 specimens in 1 taxon.
Water temperature and chemistry ranges based on 732 samples.

Environmental ranges
  Depth range (m): -99 - 260
  Temperature range (°C): 6.054 - 25.634
  Nitrate (umol/L): 0.289 - 13.639
  Salinity (PPS): 32.282 - 36.231
  Oxygen (ml/l): 4.099 - 6.764
  Phosphate (umol/l): 0.093 - 0.963
  Silicate (umol/l): 0.756 - 7.673

Graphical representation

Depth range (m): -99 - 260

Temperature range (°C): 6.054 - 25.634

Nitrate (umol/L): 0.289 - 13.639

Salinity (PPS): 32.282 - 36.231

Oxygen (ml/l): 4.099 - 6.764

Phosphate (umol/l): 0.093 - 0.963

Silicate (umol/l): 0.756 - 7.673
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Migration

Alien species

De Amerikaanse zwaardschede Ensis directus kwam oorspronkelijk enkel voor aan de Amerikaanse oostkust maar werd door transport (van larven) in het ballastwater van vrachtschepen naar Europa gebracht. In 1987 werden op het strand van Oostduinkerke de eerste schelpen van deze soort gevonden. Al gauw was de volledige kustlijn bevolkt. De Amerikaanse zwaardschede is een uitgesproken opportunist. De aanwezigheid van de soort heeft voor en nadelen. Enerzijds kan deze zwaardschede gevist en geconsumeerd worden en ook als voedsel dienen voor vogels en vissen, anderzijds kunnen ze vissersnetten beschadigen en mogelijk een negatief effect hebben op de biodiversiteit.
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Alien species

The American jack knife clam Ensis directus originates from the American east coast, and came to Europe through transport (of its larvae) in ballast water of cargo ships. In 1987, the first shells of the American jack knife clam were found on the beach of Oostduinkerke. Soon, the whole coastline was populated. The American jack knife clam is an opportunistic species. The impact on the ecosystem is twofold. Local economy can benefit from this species, as it can be fished and consumed, although the clam is also known to damage fishing nets. Although the species may serve as food for sea birds, its also feared that the American jack knife clam might negatively influence biodiversity.
  • VLIZ Alien Species Consortium
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Trophic Strategy

Food Habits

Ensis directus is a filter feeder that filters water through its shell in order to obtain food. When feeding, E. directus stays very close to the surface and its siphons are sticking up through the surface. The water is drawn into the shell through the mantle cavity by cilia. These cilia cover the ctenidia, or gills, in the clam. It passes along the gills and combines with mucous. The food is now trapped and the cilia drive the food into the digestive tract.

(Jobin and Jobin 1997)

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Life History and Behavior

Reproduction

There are separate male and female sexes in Ensis directus. The males release their sperm into the water and the sperm enters the female through openings. The eggs are fertilized in the interior of the gill by the sperm and these newly fertilized zygotes develop into larva. This larva is then released into the surrounding water. There are two larval stages. The first stage is the trocophore stage that has small larvae that are free swimming. They are pear shaped, translucent, and ciliated. The second stage is the veliger stage, which is also a free-swimming larval stage. It has a very long pelagic or plankton stage, which means that the larvae float freely within the water. This allows for the larvae to spread over large distances. This larva then settles onto the sand or mud and begins to develop into an adult. The body will develop as well as the mantle. The mantle will then secrete and line the shell.

(Kindersley 2001; Ogden 2001)

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Ensis directus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

Download FASTA File
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Statistics of barcoding coverage: Ensis directus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 6
Specimens with Barcodes: 7
Species With Barcodes: 1
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Genomic DNA is available from 1 specimen with morphological vouchers housed at British Antarctic Survey
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Conservation

Conservation Status

US Federal List: no special status

CITES: no special status

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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Unknown. The Jackknife clam burrows deep and surfaces only to obtain food and water. There does not seem to be any negative effect of the clam on humans.

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Economic Importance for Humans: Positive

Ensis directus is a very fast burrower and very difficult to catch while it is still alive. However, when it is caught it can be sold and eaten like many other types of clams. E. directus is in season during the months of July-September.

(Great Northern Products. 2001; Cooper 1960)

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Wikipedia

Atlantic jackknife clam

Jackknife clam, cooked, valves open

The Atlantic jackknife clam, Ensis directus, also known as the bamboo clam, American jackknife clam or razor clam (but note that "razor clam" sometimes refers to different species), is a large species of edible marine bivalve mollusc, found on the North American Atlantic coast, from Canada to South Carolina as well as in Europe.

This clam lives in sand and mud and is found in intertidal or subtidal zones in bays and estuaries. Because of its streamlined shell and strong foot, it can burrow in wet sand very quickly, and is also able to swim. It gets its name from the rim of the shell being extremely sharp (stepping on one can cause injury) and the shape of the clam overall bearing a strong resemblance to an old fashioned straight razor.

At low tide the position of the Atlantic jackknife clam is revealed by a keyhole-shaped opening in the sand; when the clam is disturbed, a small jet of water squirts from this opening as the clam starts to dig. This species' remarkable speed in digging can easily outstrip a human digger, making the clam difficult to catch. Thus the species is not often commercially fished, even though it is widely regarded as a delicacy: in coastal Massachusetts, they are sought after in the summer by locals to make home cooked clam strips and most towns insist upon regulations dictating how many can be taken at a time.[1] The easiest way to catch jackknives is to pour salt on the characteristic breathing holes. The clam will try to escape the salt by coming up out of its hole, at which point you can gently grab the shell and pull it out of the ground.

Predators of Ensis directus other than humans include birds, such as the ring-billed gull (Larus delawarensis) in North America and the Eurasian oystercatcher (Haematopus ostralegus) in Europe, and the nemertean worm Cerebratulus lacteus.[2]

The Atlantic jackknife clam is now also found in northwestern Europe, where it is regarded as a harmful exotic species. It was first recorded in Europe in 1978/79, in the Elbe estuary.

See also[edit]

References[edit]

  • The Long Island Shell Club, 1988. The Seashells of Long Island, the Long Island Shell Club Inc, New York State
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