Black Worm V

Black Worm V


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Blood Flow and Pulsations

Place a worm on moist filter paper and view it under a stereomicroscope. You notice immediately many large and small blood vessels coursing through its body. The two largest vessels, running lengthwise along the worm, are the dorsal and ventral blood vessels. As in their terrestrial relatives (namely, earthworms), the dorsal blood vessel of blackworms is pulsatile, and contraction waves in the wall of this vessel pump blood from the tail toward the head (Fig. 5). The small, segmentally arranged lateral branches of the dorsal vessel are a unique and diagnostic feature of blackworms. Found in each segment, these branches are also pulsatile and seem to act as auxiliary pumps.

Pulsations of the dorsal vessel help to deliver blood throughout the entire body after it is oxygenated in the worm's protruding tail. A closer look at the dorsal blood vessel in tail segments reveals several important anatomical and physiological adaptations for gas exchange, including an expanded volume of the dorsal vessel, rapid pulsation rates, and close contact between the vessel and the dorsal epidermis. You can devise many novel experiments to measure pulse rates and the velocity of pulse waves under various conditions, in either whole worms or worm fragments.

The freshwater blackworm, Lumbriculus variegatus, is a "user-friendly" creature with an unusual combination of biological features and functions that can be easily observed, in either whole worms or worm fragments. With so little previous research done on this organism, there are many potential opportunities for students to make original observations and contributions regarding its development, behavior, physiology, and ecology.

Image of pulsation waves in dorsal blood vessel

Figure 5 (a) Image of pulsation waves in dorsal blood vessel .

 

Image of lateral branches of the dorsal vessel.

Figure 5 (b) Image of lateral branches of the dorsal vessel.

Further Reading

Brinkhurst, R. O., and S. R. Gelder. 1991. Annelida: Oligochaeta and Branchiobdellida. In Ecology and Classification of North American Freshwater Invertebrates (T. H. Thorp and A. P. Covich, eds.). Academic Press, New York.

Drewes, C. D., and C. R. Fourtner. 1990. Morphallaxis in an aquatic oligochaete, Lumbriculus variegatus: Reorganization of escape reflexes in regenerating body fragments. Developmental Biology 138: 94103.

Drewes, C. D., and C. R. Fourtner. 1989. Hindsight and rapid escape in a freshwater oligochaete. Biological Bulletin (Woods Hole) 177: 363371.

Acknowledgment

Supported, in part, by the Howard Hughes Medical Institute Education Initiative in the Biological Sciences at Iowa State University, Ames, Iowa.

Carolina Biological Supply Compagny, Article used by permission

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