Clams may be unassuming characters resting (happily) on the sandy seabed, but beneath their hard shells they have some interesting features. They may not have a brain, but they have a foot to help them dig. They begin their lives as males and end as females. Some produce pearls. And with over 15,000 species worldwide, they vary in size, shape and colour and enjoy living in waters all over the world.
If you want to learn a fact or two about clams, then read on...
Large family
Clams are a type of invertebrate (an animal without a backbone) and belong to the world's second largest animal family: Mollusca phylum, of which there are 100,000 family members. Within this phylum, clams are classified as bivalve shellfish, since their bodies are enclosed within two hard shells that hinge at the base. The clam family is large; 15,000 species large to be precise.
Sizes
As we just mentioned, there are around 15,000 species of clams. So, as you can imagine they come in a wide range of sizes, from tiny to enormous. The largest is the giant clam (Tridacna gigas), growing up to four feet long and weighing more than 500 pounds. On the other end of the spectrum, species like the pygmy pea clam can be as small as two millimetres.
Clams have a foot
Did you know that clams have a foot? They use this foot to help anchor themselves into the sand, move around and even burrow beneath the seabed. Some clams can dig at impressive speeds; the razor clam can bury itself up to 70cm underground to hide from predators. One of our favourite facts about clams is that when needed, clams can dig at a rate of an inch per second to get away from predators. They do this by using rapid movements of their foot to fluidise the ground around them, essentially turning it into quicksand.
No brain, no problem
Clams don't have a brain. Instead, clams have clusters of nerve cells called ganglia, along with sensory organs that help them sense their environment. These allow them to detect changes in light, vibrations and even the presence of chemicals in the water around them. If they detect any changes in their surroundings, they can start to dig with their foot to avoid predators.
Hermaphrodites
An interesting fact about clams is that they're sequential hermaphrodites, meaning they can change their gender over the course of their lives. Typically, a clam will start life as a male producing sperm. However, as it matures and grows larger, it may transition into a female and begin producing eggs instead. This gender change is often linked to ensuring better reproductive success, as larger clams have more energy and resources to produce eggs, which require more energy than producing sperm.
In and out
How do clams gather their nutrients? Clams have two siphons which help them get the food they need to hop around the sea floor. One siphon is responsible for drawing in water that contains food particles and oxygen, while the other siphon expels waste and excess water.
Symbiotic relationships
Not all clams rely on their siphons to gather food. A fact about giant clams that you may not know is that some have a symbiotic relationship with microalgae. The clams provide the microalgae with a safe place to live and access to sunlight for photosynthesis. In return, the microalgae produce byproducts like sugars, which the clams use for energy and growth, allowing them to grow, well, giant.
Long lives
Clams may be unassuming, but if left alone in the right environment they can live for an astonishingly long time. The ocean quahog (Arctica islandica) holds the record for the longest-living non-colonial animal, with one specimen called Ming, reaching 507 years old. While some clams live for centuries, most live between a year and 40 years depending on their environments.
Life cycle
Clams are broadcast spawners, meaning they release sperm and eggs into the water for fertilisation. After hatching, they go through free-swimming larval stages. As their shells grow heavier, they settle onto the bottom, using their muscular foot to find a suitable spot and anchor themselves down. While small clams will continue to move around, giant clams will anchor and stay put for the duration of their long lives.
Filter feeders
Our final fact about clams is that they're remarkable natural water filters. In fact, clams can purify up to 50 gallons of water per day by filtering out plankton, algae and other small particles. This helps keep aquatic ecosystems clean and supports clearer water, allowing more light to reach photosynthetic organisms like seagrasses. This ability to remove harmful algae means that clams are vital when it comes to maintaining water quality. Even a small clam, just one to two inches in size, can filter up to four-and-a-half gallons of water a day. Due to their filter-feeding nature, clams are often used as bioindicators to assess the health of an ecosystem.
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