Mud piddock siphons can be clearly seen in this photo and on the nearby shoreline. Empty burrows

can also be easily found and, on

occasion, shell fragments. truncata

Class:

Order: Myoida Family: Pholadidae Genus: Barnea

Distribution Barnea species are distributed mainly along the Atlantic and This global Family of Pacific coasts of the American continent, or in the Indo-West Pholadidae is commonly Pacific region. These two groups have distinct features and known as piddocks or structures. Barnea truncata occurs from eastern Canada to Florida, angelwings. It is split into the Gulf of Mexico, South America, and also West Africa. Its several genera, one of previous southern range (21ºLat S, Brazil) has now extended to which is Barnea. This genus the intertidal zone of Bahia Blanca Estuary Argentina (38ºS). contains several species and Larval transport by shipping is the probable entry route. B. truncata, the Atlantic In Canada there is a very unique and disjunct population in the mud-piddock, is one of Minas Basin of the Bay of Fundy. They populate three separate them. It occurs from Nova areas of this basin, the most accessible being at Burntcoat Head. Scotia, Canada sporadically Nova Scotian mud piddocks are isolated from those further to south along the Atlantic the south (350 km) in Maine, which is also a disjunct population. coast into South America. These are the only mud piddocks in all of Canada.

Habitat They are highly specialized in burrowing into inorganic and These marine bivalves are organic substrates of variable hardness by using their shell to intertidal burrowers. They mechanically erode the substratum. bore into substrates of In Canada the species is restricted to settling on and burrowing variable hardness, building in a single geological formation, red-mudstone associated with tubular burrows. Sites -age sandstones in the Minas Basin. Adults are immobile selected vary regionally and and are dependant on this specific substrate in the intertidal include marine peats, firm zone. This habitat type is very limited in size and is unlikely to muds, mudstone, and on ever expand. It is more than likely to diminish. occasion wood. The Minas Basin has a large tidal range, resulting in highly Food oxygenated waters with considerable particulate food resources. They are suspension filter The incoming particulates such as phytoplankton and other feeders. Particles are organic matter enter through the adult piddock’s incurrent extracted from water as it is siphon. Waste is carried away via the excurrent siphon. drawn into the body cavity. Eggs and sperm are discharged during spawning in a steady Reproduction stream through the siphon. They usually spawn in late spring The sexes are separate. and summer when water temperatures rise. Fertilized eggs Eggs and sperm produced become free drifting larvae. They are widely dispersed. are fertilized externally.

Development The first drifting larval stage lasts up to a little over a month. Larval development has They have two major features, a hinge and colouring. The distinct stages, going from hinge has four interlocking teeth, one being more prominent trocophore to veliger larvae. than the others. Colouring includes two distinguishable rings, In the first stage a hinge is one dark, and one light, around the peripheral edge. A pinkish very clear and defined. The hue is obvious when many larvae are grouped together. second stage veliger larvae The veliger larvae go through several major changes, both develop a ciliated velum external and internal. A functioning foot is developed. This is used for swimming and also used when they are ready to settle on suitable substrates. Once for trapping minute settled they begin to burrow. Metamorphosis now takes place particles of food. At this from veliger larvae into juvenile piddocks. These burrowing second stage the rate of juveniles continue to grow and develop into the adult form. development relates to food availability. The species has distinct male and female specimens but is not externally sexually dimorphic, the male and Characteristics female look the same. They have laterally compressed In the Canadian population, bodies, enclosed by a shell in 2 parts called valves. the adult has a greyish- These have interlocking teeth. The shell is composed white shell, typically 3-5 cm of calcium carbonate. It serves its purpose but is quite in length. The small, very fragile and does not usually survive being dug up. attractive shell is thin and Sculpturing is strong at the more pointed anterior end delicate. It is elongated and but diminishes in strength on the truncate posterior gapes at both the anterior end. They reach sexual maturity at about 2 years and and posterior ends. They can live to almost 9 years of age entombed in their are also known as Fallen or individual burrows with only their siphons showing. True Angelwings. at the surface. The two siphons are sheathed together.

Adaptations Each piddock creates and expands its own This intriguing has burrow. This is accomplished at the pointed end the ability to tunnel down of the shell with tiny interlocking teeth or ridges. into the red-mudstone of Using longitudinal movements, adductor muscles the local shoreline. The and the foot wedge the shell back and forth, adult becomes a stationary, propelling it forward into the substrate. Dirt from boring, suspension feeder. the excavation is cleared by water expelled from It remains all of its adult life the mantle cavity. Because the species grows in in the protective burrow it size as it continues to burrow, the top of the bore hole is creates for itself. narrower than the piddock, creating a tomb. Their life- supporting siphons extend from the burrow to the surface. Status/Threats The primary threats to the Any changes in sedimentation deposits Minas Basin population are can result in smothering of individuals, habitat degradation and if not sites. Human induced climate change exposure to sediment. will impact many species globally. COSEWIC designation is Threatened. Sightings in Nova Scotia Mud piddocks and their habitat are Limited to a few areas in protected under the federal Fisheries Act. the Minas Basin.