Mya arenaria

Biology/Natural History: This clam has been introduced from the Atlantic, being first seen in San Francisco Bay in 1874. It slowly spread north, and reached Alaska in the 1950's. By the 1920's it seems to have largely displaced the native clams in San Francisco Bay. This clam has long siphons, and can be 20-35 cm below the surface. It can live anaerobically for several days, and dissolves the shell to buffer acidity in these conditions. In San Francisco Bay its optimal intertidal depth is 30 cm above zero tide line. The siphons appear as slits at the surface of the mud, and emit a spurt of water as they contract if one steps near them. This clam burrows only slowly, without using the foot much. Burrowing is by closing the valves and forcefully ejecting water. Predators include skates, rays, and sharks. Predators in Europe include oystercatchers and curlews, from which the clams have a refuge in depth if over 15 cm deep. May contain pea crab symbionts. Mature at about 2-4.5 cm, and spawn in spring or summer. This species is highly esteemed for food.

 Mya arenaria is a large long-lived bivalve. The shell is dirty white or fawn in colour with a fawn or light yellow periostracum. Large specimens may reach 12 -15 cm in length. The shell is oval in outline, marked by conspicuous concentric lines with dissimilar valves, the right being slightly more convex than the left, and slightly anterior beaks (umbones). The shell gapes posteriorly. The shell hinge bears no teeth but the left valve bears a large spoon shaped chondrophore to which the ligament is attached. However, there is considerable variation in shell outline, texture and thickness. The interior of the shell is white with a deep pallial sinus, and anterior and posterior adductor muscle scars. The foot is small and muscular and the mantle edges are fused except at the pedal gape and ends of siphons. The exhalent and inhalent siphons are fused along their length, contractile, and capable of considerable extension to reach the surface (about 20cm or up to 40cm in large specimens) where they leave a characteristic 'key-hole' shaped opening in the sediment.Common names include, the 'sand gaper', 'soft clam', 'soft-shelled clam', 'steamer clam' and the 'nannynose'. The literature on Mya arenaria is extensive and this Key Information review is based upon more detailed reviews by Clay (1966), Newell & Hidu (1986) and Strasser (1999).

As with other members of Family Myidae, this species has a shelflike or spoonlike chondrophore projecting from the hinge plate of the left valve, has two adductor muscles of similar size, and no radial ribs. Mya arenaria has a well-developed, deep pallial sinus (photo). The chondrophore (on the left valve) is well-developed, projecting as far or nearly as far as it is wide (photo). The umbones are only slightly anterior to the middle (photo). The hinge ligament is internal, attached to the chondrophore (photo). The posterior end of the shell is less smoothly rounded than is the anterior but it is not truncate. The valves may gape slightly at each end, especially the posterior end (photo). The shell is brittle and chalky white or gray outside with some light yellow or brownish periostracum and uneven concentric rings. The siphons are light brown with darker tips (photo). Length to 17 cm, most often 10 cm or less in our area.

Sand gapers are large shellfish. The large shell valves, which you sometimes find on the beach, don't close entirely. They gape a bit. That is why this animal is called a sand gaper. Originally, they came from America. The Vikings brought this animal from North America to Europe. That may not seem so strange. However, the Vikings lived before Columbus. The presence of sand gapers in Europe indicates that the Vikings had contact with America. This means that Columbus was not the first to travel to America.

Circumboreal, not reaching the Mediterranean

Labrador to off Georgia; Western Europe

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Geographical Range: Norton Sound, AK to Elkhorn Slough, Monterey, CA; Japan, Kamchatka, North Atlantic, North and Baltic Seas

How to Distinguish from Similar Species: Mya truncata and Platyodon cancellatus have a truncate posterior end and rarely exceed 7 cm. This species may be found along with horse clams such as Tresus capax and may look like a small individual of that species or especially like Tresus nuttallii, but the horse clams such Tresus capax have a chondrophore in BOTH valves and a large gape between the valves at the posterior end (photo).

intertidal, bathyal, infralittoral and circalittoral of the Gulf and estuary

Depth range based on 3325 specimens in 1 taxon.
Water temperature and chemistry ranges based on 95 samples.

Environmental ranges
  Depth range (m): -99 - 329
  Temperature range (°C): 4.685 - 23.636
  Nitrate (umol/L): 0.325 - 13.953
  Salinity (PPS): 6.151 - 35.785
  Oxygen (ml/l): 4.747 - 8.227
  Phosphate (umol/l): 0.110 - 1.208
  Silicate (umol/l): 0.756 - 16.169

Graphical representation

Depth range (m): -99 - 329

Temperature range (°C): 4.685 - 23.636

Nitrate (umol/L): 0.325 - 13.953

Salinity (PPS): 6.151 - 35.785

Oxygen (ml/l): 4.747 - 8.227

Phosphate (umol/l): 0.110 - 1.208

Silicate (umol/l): 0.756 - 16.169
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

 Mya arenaria lives in burrows up to 50 cm deep in sand, mud, sandy mud, and sandy gravels from the mid shore to the shallow sublittoral, sometimes to a depth of 192 m. Often abundant on estuarine flats where it can survive at salinities as low as 4-5 psu.

Depth Range: Intertidal (optimum depth in San Francisco Bay is 30 cm above zero tide line)

Habitat: In mud or sandy mud, sometimes mixed with gravel. Common in estuaries and other areas of reduced salinity (to as low as 23% seawater).

De strandgaper Mya arenaria zou uit Amerika in de 16e of 17e eeuw geïntroduceerd zijn. Er zijn echter aanwijzingen dat de Vikingen deze soort - intentioneel als voedsel of toevallig in het water in de onderste regio van het schip - al omstreeks 1245-1295 naar Europa brachten. Omwille van de mogelijkheid om in verschillende omgevingstypes te overleven, heeft de strandgaper een wereldwijde verspreiding. Het is een grote schelpensoort - wel tot 15 centimeter - die wanneer hij in grote aantallen aanwezig is, de omgeving sterk kan beïnvloeden. Omwille van de ingegraven levenswijze (soms tot wel 50 centimeter diep in de zeebodem!) is de aanwezigheid ervan vaak moeilijk vast te stellen.

It is believed that the softshell or sand gaper Mya arenaria was introduced from America in the 16th or 17th century. There is also evidence that Vikings brought this species to Europe around 1245-1295, intentionally as food or accidentally in bilge water. Because the sand gaper is able to survive in different types of environments, it has a worldwide distribution. It is a large clamp – up to 15 centimetres – which, when abundantly present, can significantly influence the environment. Because of its entrenched way of life (sometimes up to 50 centimetres deep in the soil!) its presence often remains unnoticed.

Mya arenaria is prey of:
Other suspension feeders
Mya arenaria
Crassostrea virginica
Polychaeta
Nereis
Macoma
meiofauna
Callinectes sapidus
Alosa pseudoharengus
Alosa chrysochloris
Anchoa mitchilli
Brevoortia tyrannus
Alosa sapidissima
Micropogonius undulatus
Trinectes maculatus
Morone americana
Arius felis
Platichthys flesus

Based on studies in:
USA: Maryland, Chesapeake Bay (Estuarine)
Scotland (Estuarine)

This list may not be complete but is based on published studies.

Mya arenaria preys on:
microzooplankton
zooplankton
Ctenophora
Chrysaora quinquecirrha
Other suspension feeders
Mya arenaria
Crassostrea virginica
Polychaeta
Nereis
Macoma
meiofauna
Crustacea
Callinectes sapidus
POM

Based on studies in:
USA: Maryland, Chesapeake Bay (Estuarine)
Scotland (Estuarine)

This list may not be complete but is based on published studies.

Genomic DNA is available from 1 specimen with morphological vouchers housed at Australia Museum

Canada

Rounded National Status Rank: NNR - Unranked

United States

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: GNR - Not Yet Ranked