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