What is worm pit

Phylum characteristics of the earthworm

Earthworms are segmented worms belonging to the Annelida tribe, which includes approximately 9,000 species and three classes. Class Oligochaeta are the freshwater worms (including earthworms); Class Polychaeta are the sea worms; and class Hirudinea are the leeches. There are several features that are common to all annelids and that serve to define the phylum.


All annelid bodies are serially divided into segments called metamers. Circular grooves on the outside of their bodies, annuli, separate the metamers. Each segment contains a representative of all major organ systems. Annelids are bilaterally symmetrical: if you divide the animal along the horizontal axis, each half will look like a mirror image of the other half.

Body wall

The body wall has an outer circular muscle layer and an inner longitudinal muscle layer. The contraction of the longitudinal body wall muscles shortens and greases the body. As the circular muscles contract, the body becomes longer and thinner. This allows the worm to dig, move on the ground, or search for prey in the surrounding water. They have a moist outer cuticle that is secreted by the epithelium, keeping them from drying out or drying out.

Chitinous setae

Marigolds are sometimes referred to as "bristle worms" because they have small setae that have hair-like protrusions from their bodies that aid in digging in the ground or swimming through water. They also serve to anchor some species in the ground, making it more difficult for predators to pull them out of their burrows. Setae are made of chitin, a tough polysaccharide that is also found in the exoskeletons of arthropods. Leeches are the exception as they have no sets.


The koelom is the body cavity. In annelids, it is well developed and divided by septa or membranes. The coelom is full of fluid and acts like a hydrostatic framework. Since the koelom is divided by a septa, the worm can move certain parts of the body separately.

Closed circulatory system

The circulatory system is closed, which means that the blood is trapped in muscular blood vessels. They have aortic arches that act as hearts to pump blood.

Complete digestive system

The digestive system is complete: it consists of a separate mouth and anus connected to the midgut by a foregut and hindgut.


Breathing in annelids occurs directly through the skin, through gills, or through parapodia, which are leg-like structures in some annelids. Earthworms take in oxygen and release carbon dioxide directly through the skin.

Excretory system

In each metamer there is a pair of nephridia, a type of primitive kidney. The celomial fluid is filtered through the nephridia via the nephrostome. The nephridia reabsorb nutrients in the nephridial duct, and the waste is excreted via the nephridiopore, which is localized by the ventral setae on the earthworm pair of ganglia and lateral nerves at each metamer. The annelid brain is rudimentary and consists of a pair of dorsal ganglia of the brain.

Sensory and reproductive system

All annelids have taste buds, photoreceptor cells to detect light, and a system of tactile organs to sense the world around them. Some, but not all, have lensed eyes. Annelids are of different sexes or are hermaphroditic, which means that the same animal has characteristics of both sexes. Earthworms develop by spiraling cleavage and mosaic formation, but some annelids reproduce asexually by budding, and some have a larval form known as a trochophore