Clams are inhabitants of aquatic environments that obtain sustenance in a distinctive manner. These bivalve mollusks, encased within a two-part shell, are non-motile filter feeders. They draw food particles directly from the water, a strategy that sustains them and contributes to the health of their ecosystems.
What Clams Eat
Clams feed on microscopic organisms and organic particles suspended in the water column. Their diet consists of phytoplankton, tiny marine plants, and various forms of detritus, including decaying organic matter and bacteria. This makes them suspension feeders, relying on water currents to bring food rather than actively hunting.
By consuming these particles, clams maintain water clarity and quality in their habitats. They remove excess nutrients and suspended particles, preventing issues like algal blooms and contributing to nutrient cycling. A single hard clam can filter several gallons of water per day.
The Filter-Feeding Process
The feeding process begins with specialized siphons extending from the clam’s shell. A clam has two siphons: an incurrent (or inhalant) siphon and an excurrent (or exhalant) siphon. The incurrent siphon draws water, suspended food particles, and oxygen into the clam’s mantle cavity.
Inside the mantle cavity, water flows over the clam’s gills, which have millions of tiny, hair-like structures called cilia. These cilia beat rhythmically, creating currents that propel water across the gill surfaces. As water passes over the gills, food particles become trapped in a layer of mucus coating the gill lamellae.
The gills serve a dual purpose: respiration by extracting oxygen from the water and food collection. Cilia on the gills transport the mucus-bound food particles along specialized grooves towards the clam’s mouth. Before ingestion, food particles reach the labial palps, two pairs of flaps located near the mouth.
The labial palps sort the collected particles. They secrete additional mucus to entangle the food and, using their cilia, differentiate edible particles from unwanted material like silt or excess phytoplankton. Desirable food is directed into the mouth. Unsuitable particles are rejected as pseudofeces, mucus-bound masses expelled from the mantle cavity without entering the digestive tract. This rejection occurs through periodic contractions of the adductor muscles, causing the shells to “clap” together and forcibly eject the pseudofeces, sometimes through the excurrent siphon.
Internal Processing and Digestion
After sorted food enters the clam’s mouth, it moves through a short esophagus into the stomach. Here, the crystalline style aids in digestion. This gelatinous, rod-like body, composed of glycoprotein, contains digestive enzymes like amylase and cellulase.
The crystalline style rotates due to ciliary action within its sac. Its projecting end abrades against a gastric shield in the stomach, continuously releasing enzymes. This process mixes and breaks down food particles. Following initial digestion, partially digested food passes into the digestive gland, also known as digestive diverticula. Further digestion and nutrient absorption occur here, with the digestive gland releasing additional enzymes.
Remaining waste travels through the intestine, where final nutrient absorption takes place. Undigested waste is collected in the rectum and expelled through the anus, which opens into the excurrent siphon. The excurrent siphon expels this waste, along with filtered water and carbon dioxide, back into the aquatic environment.