Segmented worms diet
The annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. The outer layer of the body consists of two layers of muscle, one layer that has fibers that run longitudinally, a second layer that has muscle fibers that run in a circular pattern. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes. Oligochaetes are full hermaphrodites and produce a ring-like cocoon around their bodies, in which the eggs and hatchlings are nourished until they are ready to emerge. Each segment contains a complete set of organs. The minority of living polychaetes whose reproduction and lifecycles are known produce trochophore larvae, that live as plankton and then sink and metamorphose into miniature adults. Most segmented worms burrow in terrestrial soils or sediments at the bottom of freshwater or marine waters. Their body is filled with fluid that gives the animal shape through hydrostatic pressure. Septa separate the segments of many species, but are poorly defined or absent in others, and Echiura and Sipuncula show no obvious signs of segmentation. This enables the segmented worm to pass a wave of movement along its body that enable it to, for example, move through loose earth (in the case of the earthworm). Segmented worms also inhabit freshwater aquatic habitats as well as moist terrestrial habitats such as forest floors. Most textbooks still use the traditional division into polychaetes (almost all marine), oligochaetes (which include earthworms) and leech -like species. Segmented worms move by coordinating their muscles along the length of their body. Each segment is separate from the others by a structure called a septa.
In many species blood circulates within blood vessels. The two layers of muscles (longitudinal and circular) can be contracted such that parts of the body can be alternately long and thin or short and thick. The mouth is located on the first segment at the head-end of the animal and the gut runs through all segments to the end where an anus is located in the tail segment. Segmented worms live in marine habitats such as the intertidal zone and near hydrothermal vents. Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. Earthworms are Oligochaetes that support terrestrial food chains both as prey and in some regions are important in aeration and enriching of soil. Segmented worms (Annelida) are a group of invertebrates that includes about 12,000 species of earthworms, ragworms and leeches. Although many species can reproduce asexually and use similar mechanisms to regenerate after severe injuries, sexual reproduction is the normal method in species whose reproduction has been studied. Each segment also has a pair of hooks and bristles and in marine species a pair of parapodia (appendages used for movement). Each segment has the same sets of organs and, in most polychates, has a pair of parapodia that many species use for locomotion. In species with well-developed septa, the blood circulates entirely within blood vessels, and the vessels in segments near the front ends of these species are often built up with muscles that act as hearts. The basic annelid form consists of multiple segments. The body cavity of a segmented worm is filled with fluid inside which the gut runs the length of the animal from head to tail. Their body consists of a head region, a tail region and a middle region of numerous repeated segments.
