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iLabs: BTW, Just What IS a Rotifer?

June 15, 2012

I guess what you call them depends on whether you want to just “call it as you see it” or impress people.

For the latter, I guess you can quote Wikipedia and say they are “microscopic and near-microscopic pseudocoelomate animals,” but everyone’s eyes will glaze over at pseudocoelomate, and many will stop listening.

You can refer to them by a common name, “wheel animals” and while that gives a hint at something about it, it’s a little too sparse on the details. Let me see if I can hit somewhere “in the middle” for a description.

For starters, use a microscope.  While some can be up to 2 mm in length, most are smaller. They are freshwater plankton, with some strains also showing up in the ocean. Their purpose in life is generally noble – they break down organic matter in soil and water environments-whether it is dead creatures or dead bits of bacteria, leaves, algae, etc.  So, they are essentially omnivores…though some species can be cannibalistic. When they’re not cleaning up organic waste, they are food for larger creatures up the food chain.

Just like people, some rotifers race around, some just sort of crawl along, and others prefer to stay put. The end of their body has “toes” that secrete a cement allowing them to attach to substrates and stay put for a while as they eat.

Appearance is also variable – while all show bilateral symmetry, and most are shaped like a column, there is quite a range of shapes as seen in a diagram from this website:

http://www.microscope-microscope.org/applications/pond-critters/animals/rotifers.jpg

The most noticeable feature of all though, is the ciliated “corona” on the head of the animal. This serves to create a current that propels food into the “funnel-like” area right before the mouth. Right beneath the mouth is a “chewing” organ or pharynx called the mastax. The simple brain is just above that organ.

closeup of a rotifer

Here is a digital photo we took on our microscope. In the center is the “clearish” looking rotifer lying almost horizontally. Notice on the right side, the ciliated head or “corona.” The body is cylindrical and at the left end (out of sight) is the foot and “toes” which are cemented into the debris. Thus, this rotifer can stay in place while it “filter feeds.”

A Google search will yield a number of academic sites that can provide more information. Here’s one:

http://www.ucmp.berkeley.edu/phyla/rotifera/rotifera.html

Also, if you click on the tag “rotifers,” which is listed at the top of this  post, it will take you to all other pages on rotifers that I post to give additional information.

Enjoy!  And I  promise…more to come on vinegar eels, Winogradsky columns, and a new topic I heard about….Duckweed. Stay tuned.  🙂

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2 Comments leave one →
  1. Maggie Ray permalink
    June 18, 2012 1:55 pm

    Keep your eye out for Tardigrades (little ” water bears” or “moss piglets”) in with the rotifers and free living nematodes. These three, along with springtails and”moss mites” are often found together making up a complete micro-ecosystem!

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