ANNELIDA
Examples: Earthworms, leeches, and ragworms.
In the last two phyla, (Platyhelminthes and Nematoda) you should have noticed a trend between the creatures that these phyla's are composed of. But, if you did not catch the drift of the similar creatures in each phylum, then you should go back and check the similarities between each phylum. So, you should have noticed that the previous phyla are mainly composed of worm-like creatures. Well, this phylum is not much different than the last two phyla. The Annelida phylum is also, mainly composed of worm-like creatures known as: "annelids" or ringed worms. This specific phylum is said to have about 17,000 species, some of them including: ragworms, earthworms, and leeches. An Annelid's body is very similar to the bodies of the creatures listed in the past two slides. The Annelid's body is "split" into identical segments and consist of the same internal organs and external "chaetae" or set of stiff bristles (hair). Now, the difference between the previous species (in the last two phyla) and the creatures in this phylum, is that these species have a circulatory system!
In the last two phyla, (Platyhelminthes and Nematoda) you should have noticed a trend between the creatures that these phyla's are composed of. But, if you did not catch the drift of the similar creatures in each phylum, then you should go back and check the similarities between each phylum. So, you should have noticed that the previous phyla are mainly composed of worm-like creatures. Well, this phylum is not much different than the last two phyla. The Annelida phylum is also, mainly composed of worm-like creatures known as: "annelids" or ringed worms. This specific phylum is said to have about 17,000 species, some of them including: ragworms, earthworms, and leeches. An Annelid's body is very similar to the bodies of the creatures listed in the past two slides. The Annelid's body is "split" into identical segments and consist of the same internal organs and external "chaetae" or set of stiff bristles (hair). Now, the difference between the previous species (in the last two phyla) and the creatures in this phylum, is that these species have a circulatory system!
CIRCULATORY SYSTEM
The worms that are in this phylum have a circulatory system, but it is closed. For example, earthworms (in this phylum) have a closed circulatory system and circulate the necessary nutrients, blood, and gases, through a series of closed vessels. The two main vessels that are used to circulate these species' nutrients, gases, etc. are known as: the dorsal and ventral blood vessels. Through the dorsal vessel, blood is circulated anteriorly or to the front sections of the creature's body. The ventral blood vessel is when the blood circulates posteriorly or to the back of the body, and supplies the body wall and and the intestine with blood. So, after the process of delivering blood by the ventral vessel to the intestine and body wall, the ventral vessel consists of several branches. Eventually, after the blood is delivered to both the intestine and body wall, then the branches split into capillary beds to receive and release the nutrients and oxygen supplied through the vessels, in the closed circulatory system!