What do freshwater mussels use to breathe? A detailed explanation of the freshwater mussel's respiratory organs
The freshwater mussel, called bangke in some places, lives on the bottom of freshwater lakes, ponds and rivers, half buried in mud and sand, with the incurrent and excurrent siphons at the rear end exposed so that water can flow in and out of the mantle cavity, thereby accomplishing feeding, respiration and the discharge of feces and metabolic waste, filter-feeding on microscopic organisms and organic particles in the water. Let's take a look below at what the respiratory organs of a freshwater mussel are!
The respiratory organs of a freshwater mussel
The respiratory organs of a freshwater mussel are gills. In the mantle cavity, on each side of the mussel's body, there are two lamellar gills (ctenidia), with the outer lamella shorter than the inner lamella. Each ctenidium is made up of an inner and an outer gill lamella, whose front, rear and ventral edges fuse into a "U" shape, while the dorsal edge forms the suprabranchial cavity. The gill lamellae are composed of many longitudinally arranged gill filaments, with cilia on the surface; the gill filaments are connected by transversely arranged interfilamentar junctions, and the small pores between the gill filaments and the interfilamentar junctions are called gill pores. Between the two gill lamellae there are interlamellar junctions that divide the gill cavity between the lamellae into many small tubes called water tubes. Blood vessels are distributed in both the interfilamentar junctions and the interlamellar junctions, and the gill filaments also contain blood vessels and several chitinous rods that serve a supporting function. As the cilia on the gills and mantle swing, they create a water current: water enters the mantle cavity through the incurrent aperture, passes through the gill pores into the water tubes, travels upward along the tubes to the suprabranchial cavity, flows backward, and is expelled from the body through the excurrent siphon. As the water passes over the gills, gas exchange takes place, and the mantle also has an auxiliary respiratory function.
What food do freshwater mussels eat
The food of the freshwater mussel consists mainly of unicellular algae, protozoa and organic debris, such as rotifers, flagellates, Euglena, Chlorella, Scenedesmus, Navicula, dinoflagellates, Tetragonium, spindle-shaped diatoms, Asterionella, fragments of crustaceans and plant leaves. The most easily digested are mainly diatoms. Mussels cannot actively chase food; they rely on the opening and closing of the shells and the beating of the cilia on the inner side of the mantle and on the gills to create a water current, so that food enters the mussel's body with the water. Food enters the mantle cavity with the water, and particles move upward along the gill filaments to the base of the gill, then forward to the labial palps; after selection by the labial palps, small particles enter the mouth, while large particles move backward along the edge of the inner gill, at the junction of the two gills pass into the mantle scar to the rear end, and are expelled from the body when the two shells snap shut. According to some counts, the amount of water flowing into a mussel's body each day can reach 40 liters.
The digestive system of a freshwater mussel
The mouth of the freshwater mussel is located below the anterior adductor muscle and is a transverse slit. On each side of the mouth there is a pair of triangular labial palps, which are large, densely covered with cilia, and have sensory and feeding functions. Behind the mouth is a short, wide esophagus, connected below to an enlarged stomach, around which there is a pair of livers that can secrete amylase and sucrase, with ducts entering the stomach. Behind the stomach is the intestine, which coils within the visceral mass, then passes into the heart, with the rectum passing through the ventricle, and the anus opening on the posterior adductor muscle, near the excurrent siphon. Between the stomach and intestine there is a crystalline style, a slender rod-like structure, thicker at the front end, with the tip varying greatly in form, appearing as a fine point, a swelling, a hook or a coil. The crystalline style is located in the intestine, with its front end protruding into the stomach and connecting with the lower part of the gastric shield. The crystalline style may be stored food; under conditions of food shortage, the crystalline style of a freshwater mussel disappears after 24 hours, and if feeding is resumed, the crystalline style reappears after several days.