Overview
In this lab, students observe vinegar eels. These small animals, barely visible without magnification, are found in unpasteurized cider vinegar, where they feed on the bacteria responsible for the conversion of apples to vinegar. Vinegar eels, Turbatrix aceti or Anguillula aceti (Muller, 1783), are examples of roundworms, or nematodes..
Needed Materials
Optional Materials
If microscopes with scanning lenses are not available, you may use stereomicroscopes (591815) (dissecting scopes). Without the substage lighting and iris diaphragm, though, students will not see as much detail as with a compound scope. Vinegar eels move vigorously and, even with Protoslo®, it may be difficult to keep them in the field of view. Removing some of the liquid under the coverslip helps confine them. Hold Bibulous Paper (634050) or a paper towel at the edge of the coverslip to absorb some of the trapped fluid.
Safety
Ensure that students understand and adhere to safe laboratory practices when performing any activity in the classroom or lab. Demonstrate the protocol for correctly using the instruments and materials necessary to complete the activities, and emphasize the importance of proper usage. Use personal protective equipment such as safety glasses or goggles, gloves, and aprons when appropriate. Model proper laboratory safety practices for your students and require them to adhere to all laboratory safety rules.
Vinegar eels are not parasitic or pathogenic. Even so, know and follow your district’s guidelines so that you are prepared should a student ingest a culture. Cultures remaining after the completion of the activities can be flushed down a sink with tap water. The chlorine or chloramine in most treated tap water will kill vinegar eels. If your tap water is not chlorinated, pipet 1 mL of household bleach (sodium hypochlorite solution) or isopropanol (rubbing alcohol) into the culture and wait 15 minutes before flushing down the sink.
Procedures
Students may work individually or in pairs.
Because of vinegar residue, the droppers used in this exercise should not be reused with cultures other than vinegar eels.
For each vinegar eel culture, set up a workstation with the following:
- vinegar eel culture
- Protoslo®
- dropping pipet
- dissecting needles (or toothpicks)
- microscope slides
- coverslips
- microscope
Optional:
If your students are not familiar with basic characteristics of animals, consider also using two other LabSheets, Introduction to Hydra and Introduction to Planaria.
Answer Key to Questions Asked on the Student Labsheet
- Is the body of the vinegar eel segmented or unsegmented?
Unsegmented - Does a vinegar eel have an anterior end? How can you tell?
Yes. They swim in one direction, with the anterior end forward unless they encounter an object, in which case they briefly reverse and then go forward again. - Where is the mouth located?
At the extreme anterior end. - Trace the digestive tract. This is best done with one of the large female worms and will probably require adjusting the iris diaphragm to achieve greater contrast. Vinegar eels are sometimes said to have a tube-within-a-tube body plan. Is this a good description, if so, why?
Yes. The body wall forms the outer tube, and the digestive tract forms the inner tube. - Do you see eyes or other specialized sense organs?
No. - Muscles produce movement by contracting. Many invertebrates that lack exoskeletons have either one or two groups of muscles responsible for movement. Longitudinal muscles shorten or flex the body when they contract. Circular muscles constrict the body. Circular muscles often produce waves of contraction that move along the body. Which type or types of muscles do vinegar eels have? How do you know?
They have longitudinal muscles only. Their bodies bend but do not constrict. - The following major animal phyla all include some worm-like forms. (Characteristics given may apply only to the worm-like members of the phylum rather than to the entire phylum.) On the basis of your observations, to which of these phyla do you think vinegar eels belong?
Nematoda
