Annelids are a very diverse group of animals. There are more than 1,300 species, including terrestrial, marine and freshwater animals.
The best known annelids are earthworms, a fundamental species for recycling organic matter. But this group also includes species as disparate as leeches or sea mice. You want to know more? In this article on our site, we tell you everything you need to know about the types of annelids and their names, examples and characteristics.
Characteristics of annelids
As we have already mentioned, the group of annelids is very diverse. In fact, the characteristics that they have in common, beyond genetics, are very scarce. However, we can name some anatomical similarities.
- Cabeza: in the front part or head are the brain and sense organs. Among these organs, there are detectors of light, chemical substances and their position in space.
- Mouth: The head is followed by a long segmented region, that is, divided into many repeating subunits. In the first of these segments is the mouth. The rest are identical or very similar subunits.
- Ano: finally, they have a final part known as pygidium in which we can observe the anus.
As a curiosity, we leave you this other article on our site about 9 boneless animals. Did you know them all?
Types of Annelid Animals
There are several very different types of annelids. They are the polychaetes, oligochaetes and hirudinomorphs. Do not worry about the names, since we are going to tell you who each of these animals are. We will also take the opportunity to talk to you about the diverse feeding of annelids
1. Polychaete annelids
Polychaetes (class Polychaeta) are the most primitive annelids. Its name means “many setae” and alludes to a kind of mobile hair that they use, mainly, to swim and propel themselves.
Within this group we can find the sea mice (family Afroditidae). These small animals live buried under the sand of the seabed, although they let part of their body out to breathe and feed. Their diet is based on the capture of worms and molluscs.
Other polychaete annelids feed on food particles floating in seawater. To do this, they generate currents thanks to a series of tentacles on their heads. The rest of their body is elongated and remains inside a tube that they make themselves with calcium carbonate. We are talking about the sea dusters (family Sabellidae).
two. Oligochaete annelids
Oligechetes are a group of annelid animals commonly known as “earthworms”. Their setae are very reduced or even do not appear.
This group includes the earthworms (order Crassiclitellata) and many groups of earthworms aquatic, both freshwater and s altwater.
Red worms (Eisenia spp.) are a group of earthworms widely used in agriculture for compost production. It is due to its great speed to transform organic matter (plant remains, feces, etc.) into fertile soil.
3. Hirudine annelids
Hirudineans (class Hirudinea) are a group of annelids that includes more than 500 species, mostly freshwater. Among them we can find invertebrate predators and many parasites.
This group includes some well-known parasites: leeches These annelids feed on the blood of other animals. To achieve this end, they have a ventral sucker through which they adhere to their host. An example of these annelids are the species of the genus Ozobranchus, which feed exclusively on the blood of turtles.
Annelid reproduction
Annelid reproduction is very complex and different in each group, even between each species. In fact, it is not always sexual, but can also be asexual. However, to simplify it, we are going to tell you only the sexual reproduction of each group.
Polychaete annelids
Polychaete annelids are dioecious animals, that is, individuals can be male or female. Males produce sperm and females produce eggs. Both types of gametes go out and the union of both (fertilization) occurs in the water The embryo that will give rise to the new individual is thus formed.
This form of reproduction is very similar to that of corals. Discover more about these incredible beings in Types of corals.
Annelids oligochaetes
Earthworms (oligochaetes) are hermaphroditic, that is, the same individual has both male and female reproductive systems. However, an individual cannot fertilize itself, but always two worms are needed One acts as a male and donates the sperm. The other has the role of female and provides the ovum.
During copulation, the two worms face facing opposite directions At this time, both the male and female expel their gametes. These are collected by a cocoon that the female has previously made thanks to a gland called the clitellum. It is in the cocoon where the union of the egg with the sperm takes place, that is, fertilization. The cocoon finally separates from the female. A small worm will come out of it.
Annelids hirudineos
Hirudine annelids are also hermaphroditic animals. Fertilization, however, is internal. The individual acting as a male introduces her penis into the female and releases sperm into her
