Regeneration
Blackworms are ideal organisms for studying segmental regeneration, developmental pattern formation, and developmental transformation of original body segments (a process called morphallaxis). Small fragments of the worm, some only a few segments in length, can be easily amputated, isolated, and stored using only basic lab supplies, such as a razor blade, filter paper disk, disposable plastic pipette, and storage containers (for example, capped centrifuge tubes or multiwell culture dishes).
Students soon discover that survival rates of body fragments are excellent, and the regeneration of missing parts occurs quickly. For example, development of a head (usually 8 new segments in length) and/or a new tail (ranging from 20 to 100 or more segments in length) is usually completed over 23 weeks (Fig. 2). Using a stereomicroscope, students can count and readily distinguish new segments from the older, original segments in the fragment.
Remarkably, the entire process of head and tail regeneration by a small body fragment can be played out within a small, tightly sealed container with as little as 12 mL of water and no food. I have continually kept isolated worm fragments alive under these conditions for more than 6 months. Such fragments gradually diminish in size, new segments readily regenerate. Because of their small size and pale color, the new segments can be easily distinguished from the older ones.
Figure 2 (a)
Image of newly regenerated head and tail ends from a 16-segment -long fragment.
Figure 2 (b)
Enlarged image of newly regenerated head.
Locomotion
Like their terrestrial relatives, blackworms move by means of circular and longitudinal muscle contractions acting on the worm's hydrostatic internal skeleton, that is, the fluid-filled body cavity (coelom) in each segment. However, blackworms are quite acrobatic. Several very different forms of locomotion are possible, depending on the sensory cues present in the worm's immediate environment. For example, if you place the worm on wet filter paper and stroke the tail lightly with a hair, it crawls forward by reflexive peristalsis. In contrast, if you stroke the head lightly under these same conditions, reverse peristaltic crawling moves the worm backwards.
