Annelida

Annelida is a group contained of tiny segmented worms, segmented meaning that these worm's bodies can be divided into three different sections. The word annelida itself actually means "little rings". Although there are about 15,000 different species in this group, all of these species can be catagorized into three different sections: oligochaeta, polychaeta and hirudinea. ALl three of these organisms have a worm like shape, but contain thicker bodies. Unlike many other organisms discussed so far, annelida are more than two cells thick.

Oligochaeta live in water habitats, both freshwater and salwater and contain over 3,000 different species.

The Hirundinea contain the fewest amount of species, around 500, and the common form of these creatures are thought of as leeches. All except one leech contains 33 body segments have two suckers, usually located on the head. Hirundinea are though to have evolved from the Oligochaeta category, and share many similarities, such as the fact that both can live in fresh or salt water environments.

Polychaeta contains the most amount of species, around 5,500. The vast majority of these animals live in the water. This large group can again be broken down into two different groups, the sedentaria which stay sedimentary and for the most part live in holes, and errantia which are more active and swim around in their environment rather than living in holes.

As one might imagine, worms primarily live in the soil and dirt. Like humans, annelida use thier mouth to eat different foods, such ad dead leaves, roots and other dead plant. This process is crucial to the environment as these organims allow for air and water enter into the soil.

Annelida do contain a digestive system, containing a mouth, anus, crop, gizzard and typhlosole. The crop, gizzard and typhlosole are used as the bodies storage, grinding and absorption compartments. The digestive system is not limited to one section of the annelida's body, but is spread out through the entire organism. Because these organisms contain a complete digestion system, annelida must have a way to discrete their waste. On each different body section there is a pore that is conected to the outside environment, and is used to discrete waste. Annelida waste includes water and nitrogen, as nitrogen is toxic to the annelida's body.

Annelids contain both female and male reproductive organs, meaning they are classified as hermaphrodites. Annelids can produce either asexually or sexually. In sexual reproduction, two annelids exchange sperm. Inside the clitellum (an organ that is designed to create an cocoon of mucous over the sperm). The cocoon moves around the body until it finds the egg. Eventualy the cocoon will be removed from the annelid, usually through the worms head, and will live in the soil until birth. In asexual reproduction, annelids can reproduce in three different ways, either: fragmentation, budding or fission.

Again, like humans annelids contain a circulatory system. They have what is called a closed circulatory system, meaning their blood flows through vessels that are closed. The system contains two different kinds of essels, dorsal and ventral. These are pumping vessels. Annelid blood contains hemoglobin, whic helps blood cell's carry oxygen.

As stated before, annelids can be found in salt and fresh water, and well as underground. For osmotic balance, salt water annelids remain balanced by drinking high amounts of water. Fresh water annelids, must eat and then disgrete their waste to maintain blalance. And for annelids that live underground, they maintain osmotic balance by eating and drinking regularly.

Annelids do not contain internal organisms that help maintain temperature control, so for a annelid to once again be in temperatures that match internal temperatures, annelids must move, usually by burrowing farther underground.

Although annelids are not actually agressive towards other organisms, they are able to protect themselves in a number of ways, Annelids often times hide, using their underground tunnels and camouflage ot hide from predators. To confuse predators, annelids are able to break off a few segments from their tales, as they are able to regrow them again.

Annelids for the most part used their eyes, located on thier head to see around the environment. Also, for many annelids, appendages are also located on the head as a way to eat and gather food.

For annelids to move, they use two major muscle groups, one muscle to shorten the body and oine to extend. Also, another muscle group compresses fluids in the annelids bodies also helping them to move. This gives the annelids, kind of wiggly and speratic movement.

Works Cited: http://www.palaeontologyonline.com/articles/2014/fossil-focus-annelids/

http://shsapbiop2-taxa.wikispaces.com/Animalia-annelida