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Clam
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Scientific Name: Pelycapoda
Number of Species/distributionThere are about 20,000 living species of clams worldwide.
- There are 260 species native to North American freshwaters.
- There are about 6 non-native (introduced) species in North America.
Most freshwater bivalves are filter feeders, eating tiny suspended particles, including plankton, detritus, and bacteria.
- Clams and mussels take in water, including any particles suspended in the water, through a small tube called the inhalant siphon.
- Food particles that are in the water are collected and sorted internally, and eventually placed into its mouth (which is internal).
- The water and any non-food particles are then released back into the environment through a second tube, called the exhalent siphon.
Clams and mussels can be found in almost all types of freshwater habitats, but are very common in large rivers and streams.
- Most burrow into the soft substrate to varying depths, while some groups live free on the sea floor.
- There are also clams and mussels that can attach themselves permanently to the substrate by using special anchoring threads called byssal threads.
Reproduction is sexual, requiring both a male and a female. Some species are hermaphrodites (which have both female and male reproductive systems).
- Male clams produce sperm and release it into the water, while females produce eggs that are retained internally.
- The sperm get drawn into the female bivalve through her siphons, and fertilization occurs.
- The larvae develop inside the shell of the female, after which the young are released into the environment where they can settle along the bottom.
- When two hermaphordites mate, they can choose who will take on the male or female role.
Freshwater bivalves have a wide range of predators;
- Numerous types of fish, such as catfish, carp, and sunfish as well as birds, crayfish, and frogs prey on clams.
- A variety of mammals, such as otters, raccoons, and muskrats also eat clams.
- When something foreign, like a grain of sand or a tiny parasite, gets stuck in the small space between a clam's body and its shell, it can sometimes be absorbed into the outer membrane of the clam (called the mantle). When this happens, the foreign object is gradually covered in layers and layers of secretions produced by the mantle. Over time, this produces a pearl.
- Clams can't breathe in an air environment. When there is a drought, however, some clams can spend months, even years, out of water. They do this by closing up and shutting down all processes except for the essential ones, and they carry these out without oxygen. The clam opens up slightly to get rid of any waste that builds up, but it only does this once in a while to avoid losing too much moisture.
- If you take a dried-out clam or mussel and put it back into the water, it will quickly open up and start taking in as much water as it can in order to get lots of oxygen and remove any waste. After 12 hours, it will be completely back to normal.
- Bivalves are kind of like trees. You can figure out their age by counting the number of growth lines on their shells, just like the rings of a tree trunk.
Sources
Brusca, R. C, and Brusca, G. J., 2003. Invertebrates, 2nd ed. Sinauer Associates, Inc., Publishers, Massachusetts. Pages 712, 730.
Canada's Aquatic Environments (2002). Bicalvia. Avaliable here
National Biological Information Infrastructure (2010). Bivalvia. Avaliable here.
Soil & Water Conservation Society of Metro Halifax (2008).Class Bivalvia. Avaliable here.
Waterwatch South Australia, Environmental Protection Authority (2006). Snails. Available here.
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