The soft body is separated into "segments," the majority of which are almost similar inside and outwardly. Because the wall possesses both longitudinal and circular muscles, it may move in more than one direction. Segmentation is the most significant difference between annelids and arthropods (the latter being a more advanced type of animal). Within the phylum Annelida, there are about 3,000 described species, most of which are marine, but some terrestrial ones have been found as well.
Their bodies consist of a digestive system, a nervous system, and a set of external organs that allow them to swim using their muscular tail and to sense their environment by means of sensory cells located on their head and body. Some species are able to bend their heads back to eat their tails themselves!
Segmented worms can grow to be over two meters long and have hundreds of segments. They are very abundant - over 5 million tons are harvested each year from coastal waters all over the world. A few land-dwelling species exist in tropical climates, but they are rare and not often seen because they are nocturnal and hide in soil or under rocks during the day.
They belong to the Enoplia superfamily. The majority of species are marine but a few species live in freshwater habitats as well.
Annelids' bodies are segmented, with robust muscles, a one-way stomach that runs through the body, a circulatory system, and a neurological system. They can reach lengths of over 20 feet and weigh up to 50 pounds.
Segmented worms belong to the phylum Annelida, which is divided into three main groups: annelids, craniates (jawless fishes), and vertebrates (including humans). Other phyla include arthropods (including insects and spiders), molluscs (snails and their allies), chordates (segmented fish), and cnidarians (stinging cells without tentacles called nematocytes).
Within the phylum Annelida, the majority of segments usually come from three germ layers: ectoderm, endoderm, and mesoderm. However, some species have more or less than three germ layers, or even no endoderm at all. For example, Achlya species contain only two germ layers (ectoderm and mesoderm) with no endoderm present. Conversely, Nemertesia is a genus of marine segmented worms with an extra layer of epithelial tissue between its ectoderm and endoderm; these worms are often referred to as "velvet worms" due to their skin texture.
Its qualities are All worms are bilaterally symmetrical, which means that their two sides are identical. They lack scales and real limbs, but may have appendages like fins and bristles. Many worms have sense organs that detect chemical changes in their surroundings, and some have light-sensing organs as well. Some worm species can move around using tools like hooks or teeth. Others drift with the current or crawl through soil or water looking for food.
Worms are among the most abundant organisms in Earth's ecosystems. There are more than 500 species of worms, and they belong to all major animal groups. Although they are often seen as pests because they can cause serious health problems if they eat enough, many types of worms are important to humans too. For example, some worms are used in medicine; others provide food when other fish are not available; still others are kept in aquariums as pets.
Worms have existed for about 700 million years and probably first appeared during the Cambrian period. They are found everywhere there is moisture and dirt, especially in places where there is no oxygen such as deep mines and caves. There are several ways that worms affect people: some species can cause diseases by biting or scratching humans who do not take proper precautions or who live in contaminated environments; others can be toxic; and some can cause damage to crops when they enter agricultural land.