Question

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external structures. (3 pts) Shell Invertebrate Zoology Laboratory 8 Invertebrate Zoology Lab M he directions in examining the bra wres as you can on the indicated qu 89 Group Questions 1) How can nematodes can get along with only longitudinal muscles in their body wall? 2) Compare and contrast the body plans of parasitic roundworms and parasitic flatworms. 3) Brachiopods were once extremely abundant, both numerically and taxonomically. Today, however, there are only about 350 living species of brachiopods, compared to 12.000 known fossil species. It has been suggested that the evolution of bivalve molluscs led to the decline in the dominance of brachiopods in the fossil record. Develop a hypothesis that explains how the evolution of bivalves caused a decline in brachiopod biodiversity and geographic distribution.

Answer 1

Nematodes are everywhere, at the poles, on top of the highest mountains, and in the deep sea trenches! About 80,000 species of Nematode have been described so far, but some authorities estimate that there may be as many as 500,000 to 100 million species in all! They live in all environments and can parasitize nearly all animals and plants. Most worms have two bands of muscles: longitudinal muscles that run the length of the body and circular muscles that form circular bands around the body. Unlike other worms that have two bands of muscles, nematodes only have longitudinal muscles.

Nematodes move by contraction of the longitudinal muscles. Because their internal pressure is high, this causes the body to flex rather than flatten, and the animal moves by thrashing back and forth. No cilia or flagellae are present.Most nematodes are dioecious.

They move using muscles, just like we move using muscles. ... This muscle action bends the worm from side to side, and the bending propels the worm forward. Nematodes are not capable of crawling, or even sliding like a snake, because all of their muscles are parallel with the body.