The annelids (from Latin annellum meaning “rings”) are invertebrate animals vermiform (wormlike) having a soft body and segmented rings. For example: the earthworm, the fire worm or the leech.
The size of annelids can vary from a millimeter to more than a meter and they are organisms that inhabit aquatic, marine and sweet, and terrestrial ecosystems .
Annelids are animals with bilateral symmetry with no skeleton. The rings that make up your body are known as “metamers” and are repeated throughout your body. Some species have the body covered with ketae, filaments that facilitate locomotion.
Annelids are invertebrate animals.
- It can serve you: Mollusks
Types of annelids
Annelids can be classified into:
- Hirudíneos . They are annelids that live in fresh water, although there are some terrestrial and marine species. They are popularly known as leeches and they are animals that do not have quetas, have suckers, are hermaphrodites and are ectoparasites or feed on vertebrates . For example: the medicinal leech.
- Oligochaetes . They are annelids, mostly terrestrial, that live in sediments and have few quetas, have clitellus (ring-shaped glandular structure) and are hermaphrodites. For example: earthworms.
- Polychaetes . They are annelids that are characterized by having an elongated and thin body covered with ketas and constitute the most numerous and primitive group of annelids. They are present mainly in the aquatic environment (especially in salt water) and feed on sediments, other marine animals or plants such as algae. For example: the sea mouse.
Characteristics of annelids
- Anatomy . They are soft-bodied triblastic animals that are worm-shaped (although not all worms are annelids) with a segmented body made up of a head, trunk, and anus. They have a segmented coelom (internal cavity in which organs and tissues are suspended) and bristles on the surface that facilitate locomotion.
- Locomotion . They do not have legs, so they move around using the quetas, which are bristle-shaped structures that they have along the surface of the body. Another way of moving is by peristalsis, that is, through waves generated by the body itself by expansion and contraction.
- Breathing. They breathe by cutaneous respiration, that is, through the skin. Some aquatic species developed gill respiration.
- Circulatory system . They have a closed circulatory system with hearts and blood vessels.
- Reproduction . They can be reproduced through:
- Sexual reproduction . They can be hermaphrodites, this means that they have both male and female reproductive organs; or have separate sexes and, in that case, the eggs are laid by the female and fertilized by the male.
- Asexual reproduction . The organism detaches the last part of its body and thus generates an independent being with identical genetic material.
- Habitat and food . They can live both in the aquatic and terrestrial environment or be hosts (parasites) within another organism.
- Aquatic annelids . They inhabit the sediment at the bottom of the river or sea and feed on microscopic organisms such as plankton. Species like the leech can feed on blood because they are external parasites.
- Terrestrial annelids . They live in humid lands and feed on sediments and nutrients found in the ground.
- Parasitic annelids or hosts . They lodge in some system or organ and feed on it.
Examples of annelids
|Alitta virens||Blood worm||Sea duster|
|Arenicola marina||Giant tube worm||Sea mouse|
|Capitella capitata||Korean earthworm||Sabellastarte indicates|
|Christmas tree worm||Californian red worm||Horse leech|
|Mud worm||Tiger worm||Spionida|