Annelida (segmented worms)
The annelid includes earthworms, lugworms, and leeches and has 15,000 known species. This phylum is known as a protsome because they have a coelom made from cell masses. The coelom is divided into seperate and repeated parts. These seperate and repeted parts in each specie is called metamerism, each segment is called a metamere. These metameres hold groups of nerve cells and excretory organs but the ventral nerve cords, a dorsal and ventral blood vessel, and the digestive tract pass through the walls of segmentation and are therefore unsegmented.
Digestion system in Annelids
Annelids have a complete digestive system with a mouth and anus. It's digestive system is basically a straight tube with the mouth and pharynx leading to an esophagus which is followed by the intestine and then anus. The Pharynx sucks in dirt, or other material, where it is moved into the crop. The food is stored until transported to the gizzard where it is mashed and made into smaller pieces. This mashed and crushed food is then chemically digested and the food is able to leave the body through the anus.
Digestive system in Earthworms
In earth worms, the digestive system begins in the mouth where food is sucked in by a pharynx where it later goes down the esophagus through peristalsis. The food then transfers to the crop, a part of the worm below the ventral nerve and ahead of the Gizzard. The food moves to intestine where the intestine can absorb the food and then exits through the anus, the last step.
Digestive system in leeches
In leeches, the digestive system starts with the jaw which is attached to the pharnyx and esophagus which heads towards the intestines and ends at the posterior sucker. In the crop, blood can expand which is why leeches' bodies grow larger when having blood. The leech can be 5 times it's own body size! Most leeches wil only digest two times a year because the stored blood remains in a liquid state without decaying or being affected by bacteria.
digestive system in lugworms
The head of the lugworm enables the lugworm to ingests sand where the worm swallows the sand or mud which connects to the mucus secreted on the everted proboscis. When the Proboscis becomes inverted, the material secreted to it us pulled to the digestive system. After the organic matter is removed from the sand , it is then dedicated from the worm.