What is phylum annelida - segmented worms, Biology

What is Phylum Annelida - Segmented Worms?

Members of this Phylum are commonly known as the segmented worms. The body of a segmented worm is made of many individual ring-like segments. The Latin word for "little ring" is "annellus," hence the name "Annelida."

Segmentation here and in the arthropods represents a distinct and significant departure from the Mollusk body plan. In terms of evolution, segmentation provides a built-in redundancy of systems. The embryo of segmented animals can develop identical segments, so that if one segment becomes damaged, other segments can take over the damaged segment's functions. Body movement is also improved, because many independent segments offer a wider range of motion than one segment by itself.

Most of the segments that form the body of annelids are for the most part identical. The anterior segments are modified to perform specific functions, depending on the type of annelid. Special functions found here would include the brain, light-sensitive eyes or antennae. Each individual segment is compartmentalized by cross walls called septa (singular: septum).

Even though each segment is partitioned, the digestive system, the nervous system and blood vessels extend along the length of the annelid body. The digestive system takes full advantage of a coelom and reflects the segmentation, in that it is divided into specialized parts called the pharynx, esophagus, crop, gizzard, and intestine. Each segment contains a pair of ganglia, or cluster of nerve cells that connect to a ventral nerve cord, providing coordination. Annelids have closed circulatory systems that use small muscular "hearts" toward the anterior of the body. A pair of organs called nephridia in each segment carries out waste excretion.

Annelids have two types of muscles. One muscle group runs longitudinally along the body from the anterior to the posterior. These muscles serve to shorten the length of the worm when they contract. The other muscle groups circle the cylindrical body rings. These circular muscles make the worm smaller in diameter when they contract. The two groups of muscles work together to move the worm's body.

Annelids can exchange gases with their surrounding medium either through gill-like structures, or directly through their skin. The digestive tracts of annelids is a complete tube that opens through a mouth and empties through an anus at the rear.

There are three classes of Annelids: Oligochaeta, Hirudinea, and the Polychaeta.

Posted Date: 5/1/2013 1:58:17 AM | Location : United States







Related Discussions:- What is phylum annelida - segmented worms, Assignment Help, Ask Question on What is phylum annelida - segmented worms, Get Answer, Expert's Help, What is phylum annelida - segmented worms Discussions

Write discussion on What is phylum annelida - segmented worms
Your posts are moderated
Related Questions
Locomotion in Annelida Before we discuss the details of locomotion in annelids, we have to recapitulate the major subdivisions of the phylum Annelida. Phylum Annelida contain

Studying life histories of insects Cut large rectangular holes in the sides of a big cardboard container and cover them with muslin folded over at the edges and gummed or paste

What are the possible sources of human embryonic stem cells? Embryonic stem cells can be derived from individual cells of an early embryo, from blood cells in the umbilical co

Define effect on Human placental lactogen in pregnancy? Human placental lactogen, with a structure similar to the growth hormone, increases throughout pregnancy. Its rate of pr

Q. Is the embryonic development in birds indirect or direct? The embryonic development is direct there is no larval stage. Q. What are the predominating chemical compounds

Q. Show the Impressions at first - Transitional Restorations? The dental technique will have modified the abutment to the desired shape and will now be able to fabricate the tr

Determine the uses of Electrical Recording - Brain function We can also learn about brain function by recording its electrical activity. In electroencephalography (EEG) and the

Define Role of Glucocorticoids in controlling gene expression? Glucocorticoids are another class of hormones involved in the regulation of lipogenic enzymes, but their role in


What is Surviving Implants It is a term described by Albrektsson that applies to implants that are still in function but have not been tested against success criteria. Such as