Overview

Brief Summary

Living Material

Little is known of the breeding season of this species, but according to Just (1939), mature animals are found at Woods Hole during July. It is probable that spawning begins before this, since in the colder waters at Prince Edward Island, larvae have been found in the plankton throughout June (Sullivan, 1948).

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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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).
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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).
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Living Material

Little is known of the breeding season of this species, but according to Just (1939), mature animals are found at Woods Hole during July. It is probable that spawning begins before this, since in the colder waters at Prince Edward Island, larvae have been found in the plankton throughout June (Sullivan, 1948).

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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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.
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Labrador to Florida
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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.
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Labrador to Florida
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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

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)

Other Physical Features: ectothermic ; bilateral symmetry

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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.
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Diagnosis

Conrad, 1843. Proc. Acad. nat. Sci. Philadelphia, 1: 325
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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.
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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.
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infralittoral and circalittoral of the Gulf and estuary
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In sand or muddy sand.
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infralittoral and circalittoral of the Gulf and estuary
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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.
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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.
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Trophic Strategy

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

Life Cycle

Later Stages of Development

The following schedule represents a range of times observed in cultures developing at laboratory temperatures ranging from 27 to 30° C. Times are recorded from insemination.

StageTime
Germinal vesicle breakdown< d>3 to 5 minutes
First polar body< d>15 to 20 minutes
Second polar body< d>25 to 30 minutes
First polar lobe< d>30 to 35 minutes
First cleavage< d>42 to 46 minutes
Second polar lobe< d>50 to 60 minutes
Second cleavage< d>58 to 65 minutes
Third cleavage< d>75 to 85 minutes
Morula< d>2-1/2 hours
Free-swimming blastula< d>3-3/4 to 4 hours
Gastrula< d>10 hours
Early trochophore< d>11 hours
Early veliger< d>27 hours

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Later Stages of Development

Razor clams are found burrowing in muddy sand habitats, which are also suitable for collecting Mya. They are procured by rapid digging at low tide. One of the best collecting grounds in the Woods Hole region is Barnstable Harbor, Mass., and another is Rand's Harbor, Mass. The sexes are separate, but cannot be distinguished externally.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Later Stages of Development

The following schedule represents a range of times observed in cultures developing at laboratory temperatures ranging from 27 to 30° C. Times are recorded from insemination.

StageTime
Germinal vesicle breakdown< d>3 to 5 minutes
First polar body< d>15 to 20 minutes
Second polar body< d>25 to 30 minutes
First polar lobe< d>30 to 35 minutes
First cleavage< d>42 to 46 minutes
Second polar lobe< d>50 to 60 minutes
Second cleavage< d>58 to 65 minutes
Third cleavage< d>75 to 85 minutes
Morula< d>2-1/2 hours
Free-swimming blastula< d>3-3/4 to 4 hours
Gastrula< d>10 hours
Early trochophore< d>11 hours
Early veliger< d>27 hours

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Later Stages of Development

Razor clams are found burrowing in muddy sand habitats, which are also suitable for collecting Mya. They are procured by rapid digging at low tide. One of the best collecting grounds in the Woods Hole region is Barnstable Harbor, Mass., and another is Rand's Harbor, Mass. The sexes are separate, but cannot be distinguished externally.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Reproduction

Fertilization and Cleavage

The ciliated gastrula is bell-shaped, with a prominent flagellum. It transforms rapidly into a typical trochophore, oval in shape. At the end of one day, the shell gland can be seen and the early veliger soon develops. The shell increases in size and has a long straight hinge. By the end of the second day, many of the veligers have lost their flagella. The velums are reduced in size. The viscera appear as an amorphous, coarse, granulated mass. The larvae are pale yellow throughout their development, darkening only just before settling to the bottom. The larval life seems to be of relatively short duration (Sullivan, 1948).

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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The Spermatozoon

Shortly after insemination, the egg rounds up and the germinal vesicle breaks down. The egg now measures 65 to 67 microns in diameter. Two polar bodies are given off, and prominent polar lobes are formed prior to each of the first two cleavages. Since the eggs are relatively transparent, the phases of spindle formation in cell division are readily distinguished. Cleavage is unequal and spiral. A ciliated blastula is formed, which hatches and swims in a clockwise circular manner at the surface. Gastrulation is by epiboly and invagination.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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The Unfertilized Ovum

The sperm are green in color, and relatively large, the head measuring 2.8 microns in width and 5.6 microns in length. They have a very long tail.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Breeding Season

In the laboratory, the animals should be kept in wet sand in an aquarium, protected from increases in temperature.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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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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Fertilization and Cleavage

The ciliated gastrula is bell-shaped, with a prominent flagellum. It transforms rapidly into a typical trochophore, oval in shape. At the end of one day, the shell gland can be seen and the early veliger soon develops. The shell increases in size and has a long straight hinge. By the end of the second day, many of the veligers have lost their flagella. The velums are reduced in size. The viscera appear as an amorphous, coarse, granulated mass. The larvae are pale yellow throughout their development, darkening only just before settling to the bottom. The larval life seems to be of relatively short duration (Sullivan, 1948).

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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The Spermatozoon

Shortly after insemination, the egg rounds up and the germinal vesicle breaks down. The egg now measures 65 to 67 microns in diameter. Two polar bodies are given off, and prominent polar lobes are formed prior to each of the first two cleavages. Since the eggs are relatively transparent, the phases of spindle formation in cell division are readily distinguished. Cleavage is unequal and spiral. A ciliated blastula is formed, which hatches and swims in a clockwise circular manner at the surface. Gastrulation is by epiboly and invagination.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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The Unfertilized Ovum

The sperm are green in color, and relatively large, the head measuring 2.8 microns in width and 5.6 microns in length. They have a very long tail.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Breeding Season

In the laboratory, the animals should be kept in wet sand in an aquarium, protected from increases in temperature.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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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.

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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

Preparation of Cultures

The egg of Ensis may be quite irregular in shape; it is enclosed in a thin vitelline membrane and surrounded by a narrow perivitelline space. The ovum is light yellowish-brown in color. It is rather granular, but moderately transparent, and has a large germinal vesicle.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Procuring Gametes

If fertilization has already taken place, eggs may be found in various stages of development. Unfertilized eggs may be inseminated by adding several pipettes-fur of sperm suspension. After a short time, change the sea water, in order to remove excess sperm. The cultures should be kept in a large amount of water and stored on a water table. The sea water in the cultures should be changed at least once a day. Loosanoff (1954) describes a method for culturing older larvae of this form.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Care of Adults

Fertilization is internal, but it is possible to obtain fully mature, unfertilized eggs. Best results are obtained with adults over five inches long. Such animals isolated in large fingerbowls will, according to Just (1939), shed naturally. Gametes may also be obtained directly from the gonads. To do this, remove one valve, exposing the gonads (white irregular masses) which lie on and around the dark brown digestive gland, just anterior to the heart. Remove the gonads with forceps or a pipette, and isolate in a watch glass. The gametes will ooze out, and when this extrusion has ceased, the gonads should be removed. The eggs are relatively clean, and require little washing. They remain fertilizable for five hours, but with a decreasing percentage of fertilization.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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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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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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Preparation of Cultures

The egg of Ensis may be quite irregular in shape; it is enclosed in a thin vitelline membrane and surrounded by a narrow perivitelline space. The ovum is light yellowish-brown in color. It is rather granular, but moderately transparent, and has a large germinal vesicle.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Source: Egg Characteristics and Breeding Season for Woods Hole Species

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Procuring Gametes

If fertilization has already taken place, eggs may be found in various stages of development. Unfertilized eggs may be inseminated by adding several pipettes-fur of sperm suspension. After a short time, change the sea water, in order to remove excess sperm. The cultures should be kept in a large amount of water and stored on a water table. The sea water in the cultures should be changed at least once a day. Loosanoff (1954) describes a method for culturing older larvae of this form.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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Source: Egg Characteristics and Breeding Season for Woods Hole Species

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Care of Adults

Fertilization is internal, but it is possible to obtain fully mature, unfertilized eggs. Best results are obtained with adults over five inches long. Such animals isolated in large fingerbowls will, according to Just (1939), shed naturally. Gametes may also be obtained directly from the gonads. To do this, remove one valve, exposing the gonads (white irregular masses) which lie on and around the dark brown digestive gland, just anterior to the heart. Remove the gonads with forceps or a pipette, and isolate in a watch glass. The gametes will ooze out, and when this extrusion has ceased, the gonads should be removed. The eggs are relatively clean, and require little washing. They remain fertilizable for five hours, but with a decreasing percentage of fertilization.

  • Just, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.
  • Loosanoff, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci., 42: 607-624.
  • Sullivan, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd. Canada, no. 77, pp. 1-36.
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© Donald P. Costello and Catherine Henley

Source: Egg Characteristics and Breeding Season for Woods Hole Species

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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. It has also been introduced to 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.

The Atlantic jackknife clam has inspired a kind of biomimetic anchor in development by a team at the Massachusetts Institute of Technology, adapting the clam's digging method for use in keeping undersea cables and potentially watercraft anchored securely.[3]

See also[edit]

References[edit]

  1. ^ "Town of Ipswich Massachusetts : Shellfish Rules & Regulations". Town.ipswich.ma.us. Retrieved 2014-02-24. 
  2. ^ "Predation of the Razor Clam Ensis directus by the Nemertean Worm Cerebratulus lacteus". Links.jstor.org. Retrieved 2014-02-24. 
  3. ^ Morgan, James. "'RoboClam' could anchor submarines". BBC News. Retrieved 17 April 2014. 
  • The Long Island Shell Club, 1988. The Seashells of Long Island, the Long Island Shell Club Inc, New York State
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