Bicoloured Razor Clam - Busselton Jetty
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Bicoloured Razor Clam

 

Occurrence at the Busselton Jetty:  The bicoloured razor clam is common in sand and seagrass around the jetty, however due to its sedentary, buried lifestyle and the heavy growth of invertebrates and algae it proves very difficult to see from the underwater observatory.

Pinna bicolor
Bicoloured Razor Clam

The bicoloured razor clam is a member of the family Pinnidae, and is the largest bivalve in the temperate waters of the south coast growing to a maximum length of 50 centimetres.  Razor clams have large, flat, wedge-shaped shells, which are embedded in the sediment with the narrow end pointed downward, leaving the broader, upper third of the body visible.  Glands on the foot secrete very fine byssal threads, securing the animal to submerged rocks or dead shells.  As it grows, it buries down further by squirting a jet of water to loosen the underlying sediment.  The clam can survive and regenerate if as much as half of the shell is damaged as the major organs are small and located in the buried, pointed end of the shell.  The shell exterior has a silvery greyish-black or brown, horny sheen, however is often heavily encrusted with invertebrates and algae, while the interior is nacreous.  Razor clams lack siphons instead using a strong jet of water to dislodge and eject any debris that may get into the shell.  As the name ‘razor clam’ indicates, they have very sharp upper  edges of the two valves and can cause a serious cut to a barefoot.  Similarly to other bivalves, bicoloured razor clams are filter feeders.  At high tide the animal will open their shells slightly, generate a current of water through the shell and sieve out food particles with enlarged gills, before clamping their shells as the tide goes out.   The tiny Pea crab (Pinnotheres sp.) is sometimes found living inside these clams.

The bicoloured razor clam produces planktonic larvae between summer and autumn.  Once settled, juveniles grow quickly and are sexually mature in one or two years.  The clams live for up to 10 years.  Their main predators are starfish and boring gastropods. 

Bicoloured razor clams occur in shallow, sheltered sand and seagrass habitats to 10 metres depth.  They range from tropical Australia around the southwest to Gulf St Vincent, South Australia and down the east coast to New South Wales, but are absent in Victoria and Tasmania.  They are also widespread in the Indo-west Pacific region, where in some parts is an important food source.

Other common names include:  Fan shell, fan clam, bicolour pen shell

References:

Edgar, G. (1997) Australian Marine Life: The Plants and Animals of Temperate Waters, Australia

Morrison, S., Storrie, A.  (1999)  Wonders of Western Waters.  Department of Conservation and Land Management, Western Australia

Morrison, S and P., Storrie, A.  (2003)  Beneath Busselton Jetty.   Department of Conservation and Land Management, Western Australia

Image:  www.jostimages.com