Which animals are annelids

Segmentation is seen in internal anatomy as well, which is called metamerism. Annelids are protostomes. These animals have well-developed neuronal and digestive systems. Some species bear a specialized band of segments known as a clitellum. Annelids show the presence numerous chitinous projections termed chaetae, and polychaetes possess parapodia. Suckers are seen in order Hirudinea. Reproductive strategies include sexual dimorphism, hermaphroditism, and serial hermaphroditism.

Internal segmentation is absent in class Hirudinea. Improve this page Learn More. Skip to main content. Module Invertebrates. Search for:. This is a combination video and animation on annelid anatomy. Try It. Sometimes the setae are located on paddle-like appendages called parapodia. Annelids are schizocoelous and with a large and well-developed true coelom i. Except in leeches, the coelom is partially subdivided by septa. Hydrostatic pressure is maintained across segments and helps maintain body rigidity, allowing muscle contractions to bend the body without collapsing it.

The internal organs of annelids are well developed. They include a closed, segmentally-arranged circulatory system.

The digestive system is a complete tube with mouth and anus. Gases are exchanged through the skin, or sometimes through specialized gills or modified parapodia. Each segment typically contains a pair of nephridia. The nervous system includes a pair of cephalic ganglia attached to double nerve cords that run the length of the animal along the ventral body wall, with ganglia and branches in each segment. And their one-way gut, running from one end of the body to the other, was a major evolutionary step.

With this digestive tract, food can be continuously taken in by the mouth, processed as it passes through the body, and released as waste at the other end.

Not only can worms continually digest their food, but they also can squirm, crawl and slither as they digest. When they eat, they also take in soil and tiny pebbles. Earthworms take in nutrients from microorganisms in the material they ingest. They then excrete wastes in the form of casts.

Casts are rich in nutrients like nitrogen, phosphorus, and potash. In addition to breaking down organic materials and adding nutrients to the soil, earthworms also help loosen the soil so air can circulate.

This helps plants grow.