Phylum Annelida
Segmented Worms
Phylum Annelida is a diverse group of animals that includes earthworms, leeches, and many marine worms. The name “annelid” comes from Latin word “annulus” which means “little ring”. The characteristic feature of this phylum is the presence of segmented bodies with a series of distinct ring-like structures.
Annelids are bilaterally symmetrical, have a true coelom (body cavity), and are triploblastic (having three germ layers). They also exhibit metamerism, i.e., the segmentation of the body into a series of repeating units called segments. Each segment has a pair of bristles or setae which aid in locomotion.
The digestive system of annelids is complete and includes a muscular pharynx, esophagus, crop/gizzard (in earthworms) and intestine. The circulatory system is closed, and blood is pumped by a dorsal vessel. Respiration is carried out by gills, skin, or body surface, depending on the species. The excretory system consists of paired nephridia, which remove waste products from the body.
Annelids have a well-developed nervous system consisting of a pair of cerebral ganglia connected to a ventral nerve cord, from which nerves extend to the various parts of the body. Sensory structures like tactile organs and eyespots are also present in some species.
Earthworms are the most common annelids, known for their soil-dwelling habits and important role in soil fertility. Leeches are used in medical treatments and have anticoagulant properties. Marine worms like polychaetes are important for their role in marine ecology and serve as a food source for many other marine organisms.
More Answers:
The Fascinating World of Hirudinea: An Overview of the Leeches’ Characteristics, Behaviors, and Medical Applications.Exploring the Key Features and Ecological Significance of Class Oligochaeta: The Few-Bristled Annelids
Discovering the Wonders of Polychaeta: Diverse Marine Worms with Unique Ecology and Anatomy