Today we mainly come to understand the shape and structure of the river mussel, from three aspects, first of all, the shell is then the mantle membrane, and finally the internal organs of the three aspects of the river mussel, so that everyone can understand the whole of the river mussel, so that in the later stage of breeding, it can be more convenient!
1. Shells are generally symmetrical left and right, and are connected at the back to form a joint. There is a more prominent part of the back, called the shell top. The rounder end of the crust is called the anterior end, the sharper end is called the posterior end, the lower part corresponding to the back is called the abdomen, and the thinner edge of the shell is called the abdomen. The shell surface has growth lines centered on the top of the tree, parallel to the ventral margin, arranged in concentric rings, and many radiative arrangements of ribs and grooves starting from the top of the tree and extending towards the ventral margin. When distinguishing between the left and right shells, the top of the shell is up, the front end is outward, and the rear end is towards the observer, then the left side is the left shell, and the right side
The one is the right shell. The distance from the top of the shell to the ventral margin is high, the distance between the front and rear end of the shell is long, and the maximum width of the left and right shells is the width of the shell. The inner surface of the shell is smooth, pearly, generally white, but also pink, purple and so on. In the crate, there are three muscle marks on the front of the shell, the largest is the anterior occlusion of the shell, the posterior front of the back is the foot muscle mark, and the abdominal is the extensor muscle mark; of the two muscle marks at the back end of the shell, the largest is the posterior closed shell muscle mark and the smaller one is the posterior constriction muscle mark. The chemical composition of the shell is mainly CaCO (about 95%) and a small amount of shellfish. It is composed of three layers of outer, medium and inner substances: the alien is called the stratum corneum, which is a thin layer of black-brown organic matter, which can resist the corrosion of acid-base substances in the water and play a protective role; the middle layer is called the prism layer, which is a very fine prismatic calcite-type calcium carbonate crystal; these two layers are secreted by the mantle membrane margin, and the area is increased with the growth of the mussel without increasing the thickness; the inner layer is called the nacre layer, which is an acid stone-type calcium carbonate crystal, which is secreted by the color line to the outer skin of the inner and outer mantle membranes, and continues to thicken with growth.
2． The mantle membrane of the mantle mussel adheres to the nacre of the shell, and is attached to the shell by the ring muscle, connecting the back and the inside. The gap between the mantle membrane and the visceral mass is called the mantle cavity. The left and right sides of the mantle membrane combine at the rear end to form the inlet pipe (equation) and the outlet pipe (dorsal square).
The dorsal process of the mantle membrane and the inner part of the mantle muscle marks are very thin, almost transparent, called the central membrane, with auxiliary respiratory function: the coat is a brown pigment line at the ventral edge, called the mantle margin; located outside the coat muscle marks, the outer food of the inner part of the mantle margin is relatively thick, and the outer skin of the prepared cell pieces is mainly taken from the limbic membrane Mantle membrane Tissue Structure can be divided into three layers: the epidermis by the visceral mass is composed of a single layer of flat epithelial cells, called the inner epidermis; the peak epidermis on the side of the shell is composed of single-layer columnar epithelial cells, called the outer skin The middle layer consists of connective tissue and a small number of muscle fibers. Only exodermal cells have the function of secreting pearls. The outer edge has three folds: by the outer fold of the shell called "raw shell protrusion", secreting keratin and colloid, the secreted keratin forms a yellow corneal membrane to encapsulate the outer fold on the shell, this structure ensures that the pearl secreted by the outer skin cells will not be lost; the middle fold has sensory cells, sensitive to external stimuli, so it is called "sensory protrusion": there are more internal muscle fibers, called "marginal membrane protrusion".
3． The internal organs of the mussel are mainly composed of axe feet, muscles, digestion, breathing, circulation, reproduction, excretion, nerves and other systems. The foot is located in the abdomen of the internal organ mass, muscular, axe-shaped, so it is called "axe foot".
The main function is to excavate the silt to lurk in the body, the slow migration mouth is located in the front of the mussel body, the posterior and lower parts of the anterior closed shell muscle, and the combination of two lip flaps on the back and abdomen is a simple transverse fissure opening, and the lip flap is densely packed with cilia, which has the effect of feeling and ingesting food. The esophagus is short, the stomach is wide, and there are brown-green digestive glands on all sides of the liver. The intestine is slender, and after three coils in the abdominal side of the visceral mass, the rectum passes through the perinear cavity and ventricles, and the posterior closure muscle is opened near the outlet pipe. The gills of the river mussel are located on both sides of the internal organ mass, and the gills on each side are composed of two pieces, the inner one is called the inner gill valve; the outer side is called the outer gill valve. Each gill flap can be divided into inner and outer flaps. The gill petals are composed of many gill filaments, the surface of the gill filaments are densely packed with cilia, and the water of the inner cloth blood vessels flows through the gills for gas exchange to complete the respiration. In addition, due to the oscillation of the cilia on the gills, water flow is promoted to form, which assists feeding. During breeding, the fertilized egg develops on the outer valve, so the outer gill valve is also called "nursery bag".
River mussels are generally hermaphrodite, with a pair of reproductive glands located above the axe foot, around the intestinal canal, and mostly in the surface of the visceral mass. At sexual maturity, the sperm nest of the male mussel is milky white, and the ovary of the female mussel is pale yellow.
Today we understand the morphological structure of the river mussel, in the next issue, I will explain some of the life habits and reproductive habits of the river mussel. I also hope that everyone can pay more attention and support more!