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Characteristics of worm

Do you like worms? Certainly, they are not the most charismatic animals in the world, in addition, the fact that some affect the health of people and other animals does not increase the appreciation for them. However, these creatures are more interesting and valuable than one might think.

A worm is considered to be an invertebrate animal with a soft body, elongated and without limbs, although some have appendages or bristles called setae . There are 3 main types of worms: flatworms, flat-bodied; the nematodes, of round body, and the annelids, of segmented body. Since “worm” is not a strictly scientific term, sometimes it is used to refer to centipedes and millipedes, and other animals of similar anatomy.

Other groups of worms are the  Chaetognatha, Gnathostomulida, the nematomorpha , the nemerteans , the hemichordates, the onychophora , the Phoronid, the Priapulida and the Sipuncula.

Characteristics of worm


There are as many types of worms as there are physical characteristics, although all are different from other animals because they have a long, soft body. The tissues of its anatomy are formed by layers and are based on internal cavities. In general, they are anatomically simple animals, of which the flatworms are more. They have a flat body instead of a cylindrical one in whose front end there are ocelli or eyes sensitive to light. Most flatworms are parasites .

Nematodes have a long, rounded body with a hard outer surface. Some have a neck that retracts and is hidden, a partially invaginated proboscis and tiny hooks that hold them to a certain place. On the other hand, the annelids are the most complex; Your body is made up of several segments with the same arrangement of nerves, blood vessels and organs. Its digestive system extends from the oral opening to the anal opening, and is constituted by a tiny mouth, a muscular pharynx, an esophagus, a crop, a gizzard and the intestine. The annelids are divided into 3 main groups: polychaetes (marine worms), oligochaetes (terrestrial and freshwater worms) and hirudineans (leeches).

Many lack a well-developed respiratory or circulatory system . In annelids, flatworms and other types of worms the skin acts as a barrier against substances from the outside, and absorbs nutrients, oxygen and other substances necessary for their nutrition and respiration. Marine worms without an excretory device, such as ketognatos, expel their waste through their skin.

Many worms move thanks to very small muscle contractions, but the bristles (setae) of the polychaetes help them move. Although they are attributed a small size, many worms can be extremely long. For example, Placentonema gigantissimum measures 8 meters in length!


The worms can live in almost the entire world and in a myriad of habitats that include sea, land, bodies of freshwater and even the intestines of other living beings. The latter are called parasitic worms. Some others are limited to living on the seashore.

They can thrive on the seabed and on coral reefs.

The polychaetes are marine, although a few are able to live in humid terrestrial environments. They can thrive on the seabed, on coral reefs and even in floating debris of inorganic matter, such as ship surfaces.


The worms can feed on bacteria, fungi, protists, decaying organic waste and, in some cases, directly from the nutrients dissolved in the water. Because terrestrial worms excrete their wastes daily in amounts similar to their own weight, they enrich the soil. Because of this, they are very appreciated by farmers and farmers .

Cestodes parasites lack mouth and digestive system, so they absorb nutrients through its very thin skin.


They spend a lot of time looking for food. Some, like earthworms, have sensory receptors in the skin with which they are guided on the ground. If it is very hot or very cold, dig deeply with the intention of coping with the temperatures.


Reproduction habits vary according to the group and the species. The most common is that the annelids and flatworms are hermaphrodite, that is, with both male and female sex organs, while the nematodes have separate sexes and are male or female. Many species reproduce asexually by fragmentation , after which two individuals originate from one.

Polychaete worms can reproduce both sexually and asexually. They can be hermaphrodites, of separated sexes or, to be males in a moment of their life and later to change of sex. Terrestrial worms are usually hermaphroditic, actively copulate and, with a bit of luck, both individuals end up with their fertilized eggs. In 2-3 weeks, the eggs hatch and pups appear.



The worms are the most abundant animals on Earth, and are not endangered globally. Despite not being loved by children and grown-ups, they are valuable for agriculture. Of course, they have multiple natural predators , among which are birds, salamanders, geckos and badgers, just to mention a few.

Parasitic worms are very dangerous for the health of living beings, as they tend to reduce their vigor and reduce their health.





Examples of Poikilothermic animals