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Razor clam

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Razor clam
Razorpile.jpg
Scientific Classification
Species

Genus Ensis

Genus Siliqua

  • S. albida
  • S. allida
  • S. alta
  • S. costata
  • S. fasciata
  • S. japonica
  • S. lucida
  • S. media
  • S. nuttallii
  • S. patula
  • S. polita
  • S. pulcella
  • S. radiata
  • S. sloati
  • S. squamata
  • s. winteriana

The Razor clams (a.k.a. jackknife clam) are any of the species of clams that belong to the taxonomic family Solenidae. The razor clams are extensively harvested throughout their range by both commercial and recreational fisheries. It has a long, slender body and can dig quickly under the sand. This interesting mollusk as a diverse number of species, and its amazing abilities and complex means of survival make it an intriguing creature to observe.

Contents

Anatomy

Unidentified razor clam

The razor clam has a slender, lengthy, [1] slightly curved shell. [2] This shell has an outer tissue-like layer called the periostracum that changes color as the bicuspid grows. When the clam is very young this layer is brown. In adolescence and adult life it is a brownish-yellow, and brown again with old age. The periostracum in large and older razorclams are usually eroded. The inner part of the shell is normally a glossy white. Occasionally, purple areas may show through this layer. A prominent rib extending from the upper part of the shell to the shell edge is also evident. [3] This shell is created by the mantle. The mantle has two parts and each part of the mantle secretes a shell. These two layers are connected by an elastic ligament that allows the shell to open and close. [4] The clam will grow about 6 cm by it's first winter and can grow up to 17 cm. [5]

Reproduction

Most jackknife clams will be sexually mature within the third and seventh growing season. Mating can occur between May and September and depends greatly on water temperature, 55°F is believed to be the perfect temperature for mating. Razor clams have two separate genders. In the species Ensis directus, the male will release sperm into the water which will enter the female through openings and are implanted in the gill with the eggs. These fertilized eggs will remain in the gills until they are larva. They are released into the surrounding water as first stage larva. The first-stage larva are free-swimming, pear-shaped, translucent, and ciliated. The first stage is considered the trocophore stage. They also go through a second larval stage called the veliger stage, which is also a free-swimming stage. This long pelagic stage allows the larvae to be scattered. Once it is done with this[6] 5 to 16 week long[7] larval stage it will settle in the sand or mud and start to develop. The body, as well as the mantle, will develop creating the shell. [8]For the species Siliqua patulaf, the eggs and sperm are released into wet sand and in the sea water. This is not an efficient method of reproduction, but the razor clam makes up for that with quantity. A female razor clam may hold anywhere from 300 thousand to 118.5 million eggs at a time. The larger the female, the larger the amount of eggs. Some razor clams can live to be over 18 years of age.[9]

Ecology

Atlantic Jackknife Clam (Ensis directus)

Razor clams live on sand beaches in low to sub-tidal zones. [10] They live at depths of 1-20 meters down in the sand. It is normally found on the East Coast of North America and Canada, but can be found in The Northern coasts of Belgium, the Netherlands, Germany, Britain, and Denmark. [11]

If the clam ever feels threatened, it can use its foot to dig into the sand, using it like a wedge. It is compressed and extended to create the hole. Some of these clams have been known to dig and disappear within 15 seconds. Once the razor clam has made it down far enough it relaxes its abductor muscle and pushes the shell open compacting the sand around it to make it hard. The foot is then made into an anchor by forcing blood to enter the foot. When the foot is enlarged, it contracts the longitudinal muscles in its foot sending the clam downwards. If the animal wishes to return to the surface, it uses its foot to push itself upward. [12] The Razor Clam only surfaces at high tide. The species Ensis directus will allow its two siphons to be exposed. These siphons are used to filter food and water. The razor clam can also swim through the water by expelling water through the shell and drawing in its foot. This action is repeated to continue the action of swimming. [13]

Razor clams are filter feeders that draw their food from the surrounding water. When feeding, the razor clam will stay close to the surface and expose its siphons. Cilia covering the gills pulls food into the shell. As the food passes along the gills (ctenidia) they combine with mucous and become trapped. The cilia along the gills then move the food to the digestive tract. They mainly feed upon small plants and plankton (animal). [14]

The clam has a positive influence on humans because it can be sold and eaten. [15]However, razor clams can damage trawls and other fishing nets. They may also leave deep cuts if stepped on. [16]

Razor Clams as a Food Source

Razor clams feed close to the surface and can be caught for food.

Razor clams have been commercially harvested since 1916 in the Cordova area of Alaska and since 1919 in the Cook Inlet area. Annual production has changed in both areas and the 1964 earthquake was unfavorable to the Cordova harvest area. Swikshak Beach on the Alaska Peninsula is the only other certified commercial harvest beach used for human consumption. It has been in use since 1929. Recreation harvesting happens mainly in Alaska. 30,000 to 35,000 days of effort are spent to harvest a million clams each year. [17]

There are some problems that can occur when considering the clam as a food source. Some people are naturally allergic to shell fish. Also PSP (paralytic shellfish poisoning) can occur if the razor clam ingests a single cell organism. Polluted habitat and storing the bivalves at too high a temperature can also cause ailments. [18]

Occasionally, small cysts of a parasitic nematode called a round worm can be implanted in the siphon of the razor clam. This worm lives commensally with the Razor Clam. This means that it benefits from the razor clam but does not cause it harm. If the razor clam is thoroughly cleaned and cooked this parasite can be removed. Sometimes this small pink or white, leech-like animal may be found inside the siphon. This nemertean worm is easily removed and does not make the clam incapable of being eaten. [19]

References

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