A small animal that lives in fresh water and has a disk in front of its body
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There are about 1800 species of rotifers, which mainly live in fresh water and have a disk at the front of their bodies.Such animals have diversity in ecology and morphology, such as free living, symbiosis and parasitism;There are free swimming in fresh water and sea water, attached living in wet soil, benthic, pipe dwelling or fixed;There are both monomer and colony.Many species are distributed worldwide.In terms of morphology, there are also many kinds of rotifersPseudocoelomaChina is quite prosperous.Rotates do not belong toBiological classificationTerms.
Rotates are animals that can only be seen under the microscope. Generally, the body length is less than 0.5mm, and the maximum body length is about 3mm, which is usually colorless and transparent. Because of different foods in the digestive tract, the body appears green, orange or brown;The body is oblong or cystic, and can be divided into inconspicuous head, trunk and tail, such as Brachinus.Different lifestyles can make great changes in the body shape, such as the types of fixed life or pipe life, with their tails extended into handles, and the floating types in the sea, with their tails shortened or disappeared, their shape changes vary from species to species.
motion
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The most superficial layer of the body wall of rotifers is the cuticle, which consists ofepithelial cellsSecretion formation, the number of epithelial cells in the same species is fixed.Within the epithelial cells are independent bundles of muscles.The ring muscles form a certain number of ring muscle bands;The longitudinal muscle bundles are relatively developed, especially in the head and tail areas. The contraction of the muscles can make the head and tail stretch out or retract the trunk.The muscles extend from the body wall to the digestive tract and other organs to fix the position of the organs.Muscles are composed of smooth muscle and striated muscle.The muscle is the pseudocoelom, which is full of coelom fluid, and the coelom fluid contains deformation cells that branch into a network.Rotifers mainly move by swimming or crawling or a combination of both.They rely on the rotation of the ciliated wheel to propel their bodies forward in swimming.The species that live on the sediments at the bottom of the water can produce secretions by the tail adhesive glands, and can do vermiculiform crawling on objects.The type of floating life in the ocean has degenerated tail, spherical trunk, long spines on the body surface to increase the surface area or oil droplets in the body to enhance the floating function. The way of movement often varies with the lifestyle.
Feeding and digestion
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Rotifers are carnivorous species, feeding on various protozoa and small freshwater animals.The mouth is located at the front and ventral surface of the body, and is often surrounded by a roulette disc. It passes directly into the pharynx from the mouth or through a small tube opening to the pharynx wall. The pharynx is spherical with thick muscles. The pharynx comes from the ectoderm, so there is a cuticle on its inner wall, and the cuticle is specialized into several large protrusions, forming a unique chewing apparatus of rotifers. Therefore, the pharynx of rotifers is also called the chewing pouch,Different rotifer chewers have different shapes and structures, and are often used as one of the characteristics of rotifer classification.Its function is mainly to grind food by mechanical digestion.In predatory rotifers, the chewing apparatus in the pharynx can be extended from the mouth to feed or hold food, and then retract with the food to grind the food in the pharynx.In the type of suspended feeding, the cilia on the cilia before or after the mouth cause water flow, and then the tiny food particles in the water flow are swept into the pharynx.It can also rely on the suction function of the pharyngeal wall muscle to suck and capture the juice in the object. Some parasitic species reduce the disc, and the pharynx completely degenerates.There are 2-7 salivary glands around the pharynx wall, which open directly to the pharynx. Its secretion can help digest food.Behind the pharynx is an enlarged stomach. There are two gastric glands on both sides of the stomach, which can secrete digestive enzymes. Food is digested and absorbed in the stomach.Rotifers are mainly extracellular digesters.After the stomach, there is a short intestine. The end of the intestine joins the excretory tube and the gonadal tube to form a cloaca, from the opening of the cloaca hole to the end of the trunk on the back of the body.
Rotifers have no respiratory and circulatory systems, and exchange gas on the body surface. They rely on the body cavity fluid to complete the transportation of substances.
