These are living on the shoreline at Petricolaria pholadiformis Burntcoat Head. Class: Bivalvia Order: Veneroida Family: Petricolidae
Genus: Petricolaria
Distribution Although originating in the western Atlantic it now has spread This species is also known to many parts of Europe. It is present in several areas of the as the American piddock. British Isles, including the Thames Estuary. Records of it It is native to the coastal occurring there go as far back as 1890. It is now well established waters of the western in the Netherlands and Denmark where it has usurped another Atlantic Ocean. It occurs in similar species of boring bivalve Barnea candida. It was more than the Gulf of St. Lawrence likely introduced to Europe by its presence in oyster shipments and Bay of Fundy south to from the USA. It now occurs on the west coast of North the Gulf of Mexico. America being introduced in the same manner.
Habitat Being a mechanical boring bivalve it has very specific habitat It is generally found in requirements. It bores into hard substrates of clay, chalk, solid shallow coastal waters of mud, peat, wood or limestone and lives in the holes it creates. depths up to 8 metres. It As it ages and grows it bores deeper into the substrate. It is usually bores holes from unable to live on open surfaces and requires a hard material to the midtide level to low bore into. water.
Upon becoming entombed in their permanent bore holes they Food are completely dependant on accessing particles of organic They are suspension filter material suspended in the water column. They breathe and filter feeders. They have two food using two siphons extending up to the water surface. siphons. By using its Intake is indiscriminate and they segregate inorganic particles incurrent siphon, water is from potential food items. This species has a high retention drawn into the body cavity efficiency for particles of a wide size range. Inorganic particles and food particles are are rejected and expelled using the excurrent siphon. extracted.
Reproduction When spawning ova and sperm (gametes) are released into the The sexes are separate. water in large numbers. Fertilization takes place when they Fertilization occurs combine and form a zygote. This (zygote) is a fertilized egg which will further develop into becoming a free swimming larva. externally.
Development The zygotes (fertilized eggs) The rate of growth is dependent on the availability of food and develop to a free-swimming water temperature. They feed on phytoplankton. A functioning (trochophore) larval stage. foot is developed. This is used when they are ready to settle on The second stage veliger suitable substrates. The combination of the foot and velum larvae go through several facilitates exploration for a suitable environment to settle into. major changes, both Metamorphosis takes place and they become juvenile piddocks external and internal. They or false angelwings, seeking permanent placement in carefully develop a ciliated velum selected, appropriate substrates. They burrow down into these used for swimming and individual home bases. They will remain in these more or less trapping food. permanent locations, continuing to grow.
Angelwing Characteristics The colour of the external The False Angelwing closely resembles the shell is off-white to fawn Angelwing Cyrtopleura costata. The main and the interior is white. distinguishing feature being it lacks the The shell is thin and fragile. spoon-shaped wings located near the beak (tip) It has an elongate oval of the (real) Angelwing. The sculptured ribbing outline and cylindrical continues along the length of the Angelwing shape. It is similar in in a fairly continuous, uniform manner where- sculpture on both sides. as the False Angelwing ribbing is more This sculpturing consists of prominent towards the anterior end. numerous concentric lines The anterior end is short and rounded, and the crossed by radiating ribs. posterior is elongated and slightly gaping. Ribs in the anterior half of Growth rings can be seen running parallel to the shell are large and the margin. The length of the shell ranges from False Angelwing coarse, with prominent 25-80 mm, but specimens are commonly up spines. to 65 mm long. They average 40 mm locally.
Adaptations They use their specially After it has carved out a home for itself it adapted shell edges to grind remains inside its burrow. It extends its life- down into hard surfaces. supporting siphons out the burrow entrance upwards towards the surface. These siphons The muscular foot grips the surface and helps to rotate filter the surrounding seawater for food items. the shell in a circular As they grow they continue to excavate the motion. A tubular burrow is walls of their burrow. Debris from this formed. This is where they expansion is flushed out of the cavity. remain for life. They can live for up to 9 years totally entombed. British bore holes
Status/Threats Larvae are heavily predated. Regional Globally the numbers are populations can be devastated by shifts in not under any threat. Severe sedimentation caused by dredging activity. storms can alter habitats.
Sightings in Nova Scotia These occur in many coastal areas.