The Phylum Annelida
Deriving from the Latin word Annellus meaning a little ring.
The phylum Annelia contains animals such as segmented worms. This phylum spans from earthworms and lugworms to leeches and marine worms. Characteristics expressed in this phylum are:
- having more than two cell layers in the body, organs, and tissues
- no jointed legs
- has a body formed of numerous rings
- body segemented both externally and internally
- etc.
Earthworm
An earthworm is one of the animals that are classified in the Annelida phylum. Like many other animals, the earthworm has a closed circulatory system. A closed circulatory system means that the blood is confined to blood vessels and its blood recirculates so it gets maximum use. The worm uses its bodies suface area to absorb oxygen from the soil instead for using lungs or gills.
The oxygen absorbed is then taken into the dorsal blood vessels and travels to five hearts by the esophagus. At the esophagus, it pumps it to the lower ventral blood vessels which then pumps the oxygen to all organs in need. To complete the loop of the circulation, in each segment there is a small blood vessel that sends the blood from the ventral vessel back to the dorsal blood vessel.
The oxygen absorbed is then taken into the dorsal blood vessels and travels to five hearts by the esophagus. At the esophagus, it pumps it to the lower ventral blood vessels which then pumps the oxygen to all organs in need. To complete the loop of the circulation, in each segment there is a small blood vessel that sends the blood from the ventral vessel back to the dorsal blood vessel.
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Leeches
Another organism in the Annelida phylum is a leech. Leeches are known for being "blood suckers" and marine organisms. Unlike other annelids, the leech has done away with bristles. Leeches can circulate gases and foods through coelomic fluids. Leeches have an open circulatory system. Since you already know what occurs in a closed circulatory system, lets tell you about a open one. In an open circulatory system ,the blood flows at a very low velocity and at low pressure due to absence of smooth muscles. There also is a direct contact between the body cells and blood so there is direct exchange of nutrients between them.
Another organism in the Annelida phylum is a leech. Leeches are known for being "blood suckers" and marine organisms. Unlike other annelids, the leech has done away with bristles. Leeches can circulate gases and foods through coelomic fluids. Leeches have an open circulatory system. Since you already know what occurs in a closed circulatory system, lets tell you about a open one. In an open circulatory system ,the blood flows at a very low velocity and at low pressure due to absence of smooth muscles. There also is a direct contact between the body cells and blood so there is direct exchange of nutrients between them.
The Animal Polychaetes in the Annelida Phylum
Polychaetes are a class of worms that are very common marine organisms in the depths of the ocean. These worms are also called bristle worms. Most Polychaetes contains a closed circulatory system but in many small polychaetes, they lack a circulatory system. The blood is effected by a system of closed vessels with muscular walls. A limited circulatory system in which some of the major blood vessels are present but capillary vessels are missing in a number of polychaete groups.