Abandoned Mine Posts

by Andy McAllister, Watershed Coordinator

Alas, the overlooked vermiform, or worm-like creatures, found living in the stream bottom are often misidentified, entirely ignored in the biological sample, or relegated to the most general of descriptions. As we delve into the world of the worm, we find that their world is infinitely more complex than it may seem, with a wide range of variations on the theme “worm.”

Horsehair worm escaping
from its blackfly host

North American Benthological Society

First, we have aquatic oligochaetes (commonly known as aquatic earthworms). Unlike their terrestrial cousins, aquatic oligochaetes are very small and often only slightly thicker than a human hair. These worms adapt well to places where organic pollution is present, such as that coming from an offending wastewater discharge or from cattle. As detritivores (animals that eat bits of dead and decaying organic matter), they happily plow thru the soft sediment, consuming just about anything small enough to fit into their mouths. But don’t be fooled: in spite of their ability to thrive in areas high in organic pollution, aquatic oligochaetes need just the right type of stream bottom. Without the right sediment, large numbers of a particular worm will have trouble surviving.

Oligochaetes are an interesting lot, exhibiting strange characteristics. Some aquatic oligochaetes can swim. Some reproduce asexually by creating long chains of zooids, miniature clones that eventually break off and become separate worms, resulting in population explosions. Some respire through their skin, while others have simple but beautiful gill structures to extract oxygen from the water.

Another less common vermiform creature is the ribbon worm, or Nemertea. Small, nondescript, and non-segmented, they too are often overlooked or misidentified in a stream biological sample. Most Nemertea are predators, and while usually marine or estuarine, there is one freshwater species. They, too, are tolerant of organic pollution, but finding a few of them in a stream should not be cause for alarm.

Other worm-like creatures that are often lumped in with the other worms are the midge larvae, sometimes called blood worms. While at first they may bear a superficial resemblance to worms, closer inspection will reveal that they are aquatic larvae of a flying insect and are not worms at all.

Not to be forgotten, horsehair worms, flat worms, and nematodes are also part of the vermiform club. Each with its own life history story, feeding type, and habitat preference, they contribute to the astounding diversity of vermiform life in a stream.

This entry was posted on Monday, November 20th, 2006 at 10:20 am and is filed under Stream Ecology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.