Annelids

__** Annelids **__ ﻿The term // annelida // refers to the ringlike appearance of the worm's body. Annelids are worms with segmented bodies, which are seperated by a septa. Their segments are modified to perform a specific function. Annelids also have a true coelom, which is a body cavity that is lined with mesoderm. The annelids have a tube-within-a-tube digestive tract where food is passed from the mouth to the anus.

__** Types of Annelids **__

Annelids are divided into three classes; oligochaetes, leeches and polychaetes. **__Oligochaete__**__**s**__ are annelids that have a streamlined body and have relatively few setae. Most oligochaetes live in fresh water or in soil. Earthworms, are an example of oligochaetes, and are long pinkish-brown worms that are found in woods, fields and gardens. Tubifex worms, another common type of oligochaete, are red aquaticlike worms that are sold in pet stores as food for tropical fish.

**__Leeche__**__**s**__ are annelids that are external parasites and suck blood and body fluids from their host. They have powerful suckers at the end of their bodies that help them cling to their host. About one-fourth of leeches are carnivorous and they feed on soft-bodied invertebrates such as snails, worms, and insect larva.

**__Polychaete__**__**s**__ are marine annelids that have paired paddlelike appendages with a lot of setae,which are brushlike structures. Polychaetes usually live in cracks on coral reefs, in sand and mud, and even out in the open ocean. Some annelids burrow through or crawl over sediment. 

__** ﻿ Feeding and Digestion **__  Annelids get their food by using their pharynx, which is a tube like structure that connects the mouth of the worm to the digestive tract. In carnivorous annelids, the pharynx has a sharp jaws which are used to attack the prey. In annelids that feed on dead vegetation, the pharynx has sticky mucus covering it. The pharynx pumps the food and soil into the esophagus, where it then moves past the crop(where food is stored) and gizzard(grinds food into smaller pieces), and then it is finally absorbed by the intestine.

**__ Circulation, Respiration, and Excretion __** ﻿  ﻿ Circulation:  Annelids have a closed circulatory system. The earthworm’s blood circulates through the dorsal(up) and ventral(down) vessels.Ring vessels, connect the two main vessels and supply the blood to the organs. ﻿ Respiration:  Annelids that live in water, breathe through gills. Annelids that live in land, take in oxygen and give off carbon dioxide through their moist skin, which is kept moist by a thin protective covering of mucus. ﻿ Excretion:  Digestive waste in annelids, passes out through the anus at the end of digestive tract. Cellular waste, nitrogen, is eliminated by the worm’s nephridia, which is the excretory organs that filter fluids.



__** Response and Movement **__  ﻿ ﻿ Response: Many annelids have many parts for detecting stimuli. They have sensory tentacles, chemical receptors, statocysts that help detect gravity, and two or more pairs of eyes. <span style="color: #4e3b30; direction: ltr; margin-bottom: 0pt; margin-left: 0.38in; margin-top: 6.24pt; text-indent: -0.38in; unicode-bidi: embed; word-break: normal;">﻿ Movement: <span style="direction: ltr; display: block; margin-bottom: 0pt; margin-left: 0.38in; margin-top: 6.24pt; text-align: left; text-indent: -0.38in; unicode-bidi: embed; word-break: normal;"> Annelids have a hydrostatic skeleton which consists of two major groups of body muscles that help the worm move.Longitudinal muscles run from the front of the worm to the rear end and are used to contract the worm to make it shorter and fatter.Circular muscles wrap around each body segment and contracts to make worm longer and thinner. <span style="color: #4e3b30; direction: ltr; margin-bottom: 0pt; margin-left: 0.38in; margin-top: 6.24pt; text-indent: -0.38in; unicode-bidi: embed; word-break: normal;">Water annelids also have parapodia which are paddlelike appendages that they use for swimming.

<span style="color: #800080; display: block; font-family: 'Times New Roman'; font-size: 26px; font-weight: normal; text-align: center;">__** Reproduction **__   Most annelids reproduce sexually. Some annelids use external fertilization and are either male or female.Other annelids are hermaphrodites, which means they contain both male and female sexual parts. To fertilize their eggs, two worms attach to each other, exchange sperm and store the sperm in sacs. When egg is ready to be fertilized, the clitellum secretes a mucus ring and egg and sperm are released. The ring will then slip off the worm’s body, form a protective cocoon and the baby worms hatch weeks later.

__ Ecology of Annelids __  <span style="direction: ltr; display: block; margin-bottom: 0pt; margin-left: 0.38in; margin-top: 7.2pt; text-align: left; text-indent: -0.38in; unicode-bidi: embed; word-break: normal;">  Earthworms spend their lives burrowing through soil, breathing it, and mixing inside of it. The tunnels that earthworms create in the soil provide passageways for the roots of plants and water. Worms mine minerals from deeper soil layers, bringing them up to the surface. E arthworms are rich in nitrogen, phosphorus, potassium, and beneficial bacteria. Birds, moles, toads, and skunks eat earthworms, and they are a very important part of their diet. In water, annelids participate in a wide range of food chains. <span style="direction: ltr; display: block; font-family: 'Century Gothic'; font-size: 19px; margin-bottom: 0pt; margin-left: 0.38in; margin-top: 7.2pt; text-align: left; text-indent: -0.38in; unicode-bidi: embed; word-break: normal;"><span style="font-family: arial,helvetica,sans-serif; font-size: 13px; line-height: 19px;">