Nereis is a type of marine worm also called a clam worm, sandworm or ragworm. It has a segmented body and is a true coelomate worm. As a result, it belongs to the phylum Annelida.
Nereis – Digestive System
The Nereis digestive system is a straight tube that runs from the anterior to the posterior end of the body cavity. It is open at both ends; the mouth is the anterior opening and the anus is the posterior opening.
Foregut
The foregut includes the mouth, buccal cavity, and pharynx. The buccal cavity, which is reached through the mouth, leads to the pharynx. The pharynx and buccal cavity continue through the peristomium and the succeeding body segments. They have cuticles lining them. Numerous locations on the cuticle thicken, forming tiny, dark-brown denticles. They are also referred to as pharyngeal teeth or cuticular teeth. Jaws are nothing but a set of these cuticular teeth that have been significantly enlarged. Each jaw is a long, rounded structure with an anteriorly pointed tip. Each jaw’s inner margin is lined with several sturdy teeth. Muscles connect each jaw to the back of the head. These muscles support jaw movement.
The pharynx protrudes, and the buccal cavity is eversible (turned inside out). The contraction of a group of muscles called the protractor muscles and the pressure of the coelomic fluid both contribute to eversion. A pair of retractor muscles that extend between the body wall and the hinder end of the pharynx is responsible for retraction.
Midgut
The oesophagus and stomach and intestine combine to form the midgut. Behind the pharynx, the oesophagus is a short tube that is divided into five segments. On either side of the oesophagus and opening into it are two oesophageal glands. The stomach and intestine follow the oesophagus.
Hindgut
The rectum and anus combine to form the hindgut. The rectum is a very small chamber behind the stomach and intestine. It is located in the final segment and is surrounded by the anus.
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