Annelids

Annelids. Phylum (phylum) comprising metamerized and vermiform invertebrate animals ; Of these, the most numerous are the marine worms with bristles and the best known are the earth worms. The Annelida (meaning small annules or rings) includes the Polychaeta (meaning many mushrooms); earthworms and freshwater worms or Oligochaeta (which means few mushrooms); the Hirudinea or marine and freshwater leeches , and two other marine classes similar to the Polychaeta: the Archiannelida (which means primitive annelids), which are small heteromorphic marine worms, and the Myzostomaria (which means sucking mouth) which are parasites of echinoderms. crinoids.

Summary

[ disguise ]

• 1 General features
• 2 Classification
  • 1 Polychaetes
    • 1.1 Characteristics and groups
    • 1.2 Habitat
    • 1.3 Playback
    • 1.4 Playback
  • 2 Oligochaetes
    • 2.1 Features
    • 2.2 Power
    • 2.3 Genres
    • 2.4 Playback
  • 3 Hirudineans
    • 3.1 Features
    • 3.2 Power
    • 3.3 Gender
    • 3.4 Playback
  • 4 Archianelids
• 3 Sources

General features

The kingdom of annelids is made up of worms that differ in their body, made up of numerous rings (annelus) or similar segments, called somites or metamers. Generally, they live in humid places, in fresh water, or are marine.

Classification

Annelids comprise an important group within the animal kingdom, since it was in them that the division into metamers (units or segments) first appeared. This segmented organic arrangement allows the animal to specialize its different parts. Three classes are distinguished:

• Marine worms or polychaetes: characterized by having abundant parapods with setae and cephalic appendages.
• Earthworms or oligochaetes: they barely have traces of setae or they are residual.
• Leeches or hirudines: They are equipped with suction cups and do not have setae.

polychaetes

Features and groups

Polychaetes are the largest group of annelids. These are marine life worms, which generally live in coastal and neritic areas. It includes two groups: the wandering ones (active pelagic life, which have equal segments, herbivorous regime and with the capacity to enter under the sand by digging galleries) and the sedentary ones (include species of sedentary life, and have the body divided into segments of different sizes). different, example of the genus arenicola ). Among sedentary polychaetes, two groups are distinguished:

• Tube-like: they are characterized by living indefinitely in chitin tubes that they themselves secrete, in the mud or attached to rocks or the shells of other animals. They feed by filtering plankton .
• Diggers: they live permanently inside galleries that dig in the mud or sand. The way they feed is through filtered detritus . The nereis , used as bait by fishermen, is an example of a burrowing polychaete.

Habitat

Polychaetes can adapt to various environmental conditions, thanks to the specialization of the different regions of the body, due to having it segmented. Each segment or metamer of a polychaete has two parapeds (lateral expansions), with setae that allow them to perform a locomotor function. The anus is located in the last segment called pygidium.

Reproduction

Reproduction

Nereis

Reproduction of polychaetes is generally sexual. In the Wanderings it takes place at a certain time of the year and in a very curious way; the back of the body changes shape and color; The posterior sexual parts detach and reach the surface of the sea, where they open and the gametes are fertilized .

Oligochaetes

Characteristics

Oligochaetes are recognized because among them are the commonly known “earthworms”, which live permanently buried in fresh water. They do not have parapods, as occurs in polychaetes, nor other appendages or eyes and are structurally simpler. They have a digestive system with some specializations, due to their detritivore activity (consumer of detritus ); The crop, gizzard and typhlosol are distinguished.

Feeding

The way oligochaetes feed is a great ecological task; They excavate galleries and digest the soil in order to absorb the nutrients contained in the organic detritus, breaking them down into smaller particles, expelling them and then depositing them on the surface. At the same time, the effect of removing the soil produces aeration of the subsoil, which, together with the reduction of larger particles, organic and mineral matter, is better used and very beneficial for the growth of plants.

Genders

The lumbricus genera, such as lumbricus terrestris , enchytraeus and allolobophora , are of great importance for the fertility of edaphic ecosystems.

Reproduction

Oligochaetes, although they are hermaphrodite animals, require two different individuals to mate for fertilization (self-fertilization does not occur).

Hirudineans

Characteristics

The hirudineans, also called achaetes (because they lack setae), are commonly known as leeches , due to their blood-sucking activity. They are segmented into fixed units, so that the number of segments is the same throughout life. They are ectoparasites, which is why they have suction cups to attach themselves to their victims, one anterior and one anal. The mouth has jaws that allow them to tear the skin of parasitized prey.

Feeding

Since they feed on blood, they absorb a protein substance ( hirudin ) in their saliva that prevents coagulation, so that blood continues to flow from the open wound. The digestive tube has a large crop divided into numerous cavities, which allows them to store more than ten times their weight; This enables them to endure long periods of fasting of up to nine months.

Gender

The genus hirudo is distinguished .

Reproduction

Hirudineans are hermaphrodites , like oligochaetes, and reproduce in a similar way.

Archianelids

Polygordius

They are small in size, unisexual, and have mainly internal segment