segmented worms

features of segmented worms

Segmented worms have a number of characteristic features. 1. The basic form consists of multiple segments, each of which has the same sets of organs and, in most, a pair of parapodia that many species use for locomotion. 2. Segmented worms have a well-developed body cavity filled with fluid. This fluid-filled cavity serves as a hydroskeleton, a supportive structure that helps move the worms muscles. Only the most primitive worms (the flatworms) lack a body cavity. 3. Segmented worms also tend to have organ systems that are more developed than the roundworms or flat- worms. Earthworms, for example, have a complete digestive tract with two openings, as well as an esophagus and intestines. The circulatory system consists of paired hearts and blood vessels. Actually there are five pairs of hearts that pump blood along the two main vessels. And the nervous system consists of the brain and a ventral nerve cord.

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segmented worms

When you think of worms, you probably picture earthworms. There are actually many types of worms, including flatworms, roundworms, and segmented worms. Earthworms are segmented worms. Segmented worms are in the phylum Annelida, which has over 22,000 known species. These worms are known as the segmented worms because their bodies are segmented, or separated into repeating units. Besides the earthworm, the segmented worms also include leeches and some marine worms. Most segmented worms like the earthworm, feed on dead organic matter. Leeches (Figure 1.1), however, can live in fresh water and suck blood from their animal host. You may have noticed many earthworms in soil. Earthworms support terrestrial ecosystems both as prey and by aerating and enriching soil.

comparison of worms

The following table compares the three worm phyla (Table 1.1). Phylum Platyhelminthes Nematoda Annelida Common Name Flatworm Roundworm Segmented worm Body Cavity Segmented No Yes Yes No No Yes Digestive System Incomplete Complete Complete

instructional diagrams

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questions

most segmented worms feed on dead organic matter.

-->  a. true

b. false

the leech is a segmented worm that feeds on live blood.

-->  a. true

b. false

worm parapodia serve what function?

a) touch

-->  b) locomotion

c) feeding

d) sight

which best describes the digestive tract of an annelid?

a) incomplete digestive tract with two openings, intestines and a stomach.

b) incomplete digestive tract with one opening, an esophagus and a stomach.

-->  c) complete digestive tract with two openings, an esophagus and intestines.

d) complete digestive tract with one opening, an esophagus and intestines.

which describes the segmented worm circulatory system?

a) a complete heart and blood vessels

-->  b) five paired hearts and blood vessels

c) five two chamber hearts and blood

d) blood and blood vessels

which worms have a body cavity?

a) flatworm and roundworm

-->  b) roundworm and segmented worm

c) segmented worm and flatworm

d) all three phyla

which worms have a complete digestive system?

a) flatworm and roundworm

-->  b) roundworm and segmented worm

c) segmented worm and flatworm

d) all three phyla

diagram questions

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