Annelida
The annelids, also called "ringed worms", formally called Annelida (from the latin word annellus, meaning "little ring") are a large phylum of segmented worms. Consisting of over 17,000 modern species including ragworms, earthworms and leeches the annelida are found in marine environments from tidal zones to hydrothermal vents, in freshwater, and in moist terrestrial environments.Annelids lack a skeletal system, but Annelids' cuticles are made of groupings of natural protein fibers. They are usually in layers that spiral in alternating directions so that the fibers inter-twine each other. These are secreted by the outermost skin layer. Under the epidermis is the dermis, which is made of connective tissue. Below that lies two layers of muscles, which develop from the lining of the coelom: circular muscles make a segment longer and slimmer when they contract, while under them are longitudinal muscles, usually four distinct strips, whose contractions make the segment shorter and fatter. The skin layer, segments and muscles are what gives the annelida's their shape.
Leeches
Leeches are segmented worms that belong to the phylum Annelida. Leeches like all other annelida do not have a skeletal system. However, Leeches do have segmentation of their bodies and do have structures that keep their body shape. Unlike other annelids, leeches have no correspondence between the external segmentation of their bodies surface with the segmentation of its internal organs. The body surface of the animal can be divided into 102 outer circular rings, whereas its internal structures are divided into 32 segments. The first four anterior segments are designated as
head segments, which include a brain and sucker. This is followed by 21 midbody segments, including two reproductive organs, and 9 pairs of testes. Finally, the last seven segments are fused to form the animal's tail sucker, as well as its posterior brain.
head segments, which include a brain and sucker. This is followed by 21 midbody segments, including two reproductive organs, and 9 pairs of testes. Finally, the last seven segments are fused to form the animal's tail sucker, as well as its posterior brain.
Nereididae
Nereididae are a family of
polychaete worms. The Family contains about 500, mostly marine, species grouped into 42 genera. They are commonly known as ragworms. Like all other Annelida Nereididae have segmented bodies that produce their shape. They have no endoskeleton or exoskeleton.
Earthworms
Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida.
In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female.The basic body plan of an earthworm is a tube, the digestive system, within a tube,
the muscular slimy, moist outer body. The body is annular, formed of segments that are most specialized in the anterior. The Earthworms have segmented bodies like all other Annelida.
In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female.The basic body plan of an earthworm is a tube, the digestive system, within a tube,
the muscular slimy, moist outer body. The body is annular, formed of segments that are most specialized in the anterior. The Earthworms have segmented bodies like all other Annelida.