Lumbriculus variegatus, more commonly known as a blackworm, is an oligochaete worm found in many freshwater habitats across Europe and North America. It is technically not microscopic, but very small and to see the details and internal anatomy, we have to use a microscope.
Blackworms are only about a millimeter in thickness, but they are able to reach a length of up to 10 centimeters. Blackworms eat things like microorganisms and decaying plant material. To digest its food, the worm has a dedicated digestive tract running down the center of the body. This is like a miniature version of the human digestive tract and works in basically the same way by squeezing ingested food through the tube with rhythmical massaging movements called peristalsis (see video further down).
Another clearly visible structure in the worm is its circulatory system. The animal lacks a true heart, but instead pumps blood through the blood vessels with several pairs of muscularized vessels able to contract and work as a heart.
The blackworm has an incredible ability to regenerate after injury. If the worm gets cut into two, each part will regenerate and become two individual worms which will be genetic clones. Adult blackworm consist of up to 250 individual segments, which all have the ability to regenerate into a fully functional worm.
The worm moves by contracting and stretching its muscle layers which cover the entire body. If the worm is illuminated with polarized light, these muscle layers will shine bright and display beautiful colors depending of the orientation in the polarized light as you can see in the clip below.
The Blackworm (Lumbriculus variegatus) viewed with different microscopy techniques
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