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The outer surface of the body wall consists of a simple columnar epithelium covered by a thin cuticle. Underneath this, in order, are a thin layer of connective tissue, a layer of circular muscle, a layer of longitudinal muscle, and a peritoneum surrounding the body cavity. Additional oblique muscles move the parapodia.
The epidermis is either a syncytium or a single layer of cells, and is covered by a thick collagenous cuticle. The cuticle is often of a complex structure and may have two or three distinct layers. Underneath the epidermis lies a layer of longitudinal muscle cells. The relatively rigid cuticle works with the muscles to create a hydroskeleton ...
Parasitic roundworms such as species of Ascaridia and Heterakis possess a single sucker at the posterior end of the body, just in front of anus, hence is often called a pre-anal sucker. Only the male roundworms have them, and are used for attachment to female during mating. The sucker is a protruding cuticle and circular in shape. [9] [10]
A. lumbricoides is the largest intestinal roundworm and is the most common helminth infection of humans worldwide. Infestation can cause morbidity by compromising nutritional status, [ 3 ] affecting cognitive processes, [ 4 ] inducing tissue reactions such as granuloma to larval stages, and by causing intestinal obstruction , which can be fatal.
Ascaris lumbricoides is a large parasitic roundworm of the genus Ascaris. It is the most common parasitic worm in humans. [1] An estimated 807 million–1.2 billion people are infected with Ascaris lumbricoides worldwide. [2]
The sensors are primarily single cells that detect light, chemicals, pressure waves and contact, and are present on the head, appendages (if any) and other parts of the body. [8] Nuchal ("on the neck") organs are paired, ciliated structures found only in polychaetes, and are thought to be chemosensors . [ 23 ]
The mesenchyme contains all the internal organs and allows the passage of oxygen, nutrients and waste products. It consists of two main types of cell: fixed cells, some of which have fluid-filled vacuoles; and stem cells, which can transform into any other type of cell, and are used in regenerating tissues after injury or asexual reproduction. [5]
The archenteron initially forms, and the mesoderm splits into two layers: the first attaches to the body wall or ectoderm, forming the parietal layer and the second surrounds the endoderm or alimentary canal forming the visceral layer. The space between the parietal layer and the visceral layer is known as the coelom or body cavity.