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iLabs: Catch-of-the-Day — Ostracods

July 9, 2014

Today one of our staff members is going to share about a new activity visitors can take part in using our research microscope: Catch-of-the-Day!

By Nancy Locquet, Micro World iLab Staff Member

In the Micro World Investigate Lab, we take good care of different kinds of microscopic pond life. How do we do this? Well, we have about fourteen cup-sized plastic containers filled with pond water. To recreate the dark natural habitat in which these organisms thrive, we place the containers under a black case in the back of the Micro World Investigate lab. Since oxygen is so crucial for these organisms, plastic air tubes aerate the pond water, creating a soothing bubbling sound.

protozoan culture with air tube

Every morning, a staff member or volunteer picks up a drop of pond water from one of these containers with a plastic water dropper to make a wet mount slide. This is done by placing the drop on a glass slide (a thin flat piece of glass (3 by 1 inches) of about 1mm thick) and covering it with a very thin glass cover (a smaller and thinner piece of glass). The wet mount slide is then examined under the EVOS research microscope. The slide is meticulously screened for microorganisms and anything we see on the screen is photographed and recorded on a daily log sheet.

catch of the day chart for protozoans

Visitors are encouraged to help us with the “catch of the day” and can mark any specimen they recognize on our “catch of the day” chart. So far we have identified and described 28 different species.

Today’s catch is our newest addition to our pond life collection. It looks like a little seed that occasionally slashes its appendages frantically in the surrounding water.


Ostracods are Metazoa and belong to the Phylum Arthropoda (as trilobites), Class Crustacea (as lobsters and crabs).

This little seed is actually called an ostracod, sometimes known as seed shrimp or mussel shrimp. This very small crustacean is about 1 mm in size (some can be between 0.2 and 30 mm) and looks like a flattened oval-shaped clam with a bivalve shell (2 parts are hinged). Their body is covered with hairs which you can see at 40x magnification. They have 7 pairs of appendages (antennae-like structures) which all have a function. The first 2 pairs are antennae, the 3rd, 4th and 5th pairs make up their mouth parts, the 6th pair is different between males and females and the last pair are cleaning tools.

Where do they usually live? These ostracods can be found crawling or burrowing into the sediment at the bottom of springs, lakes and oceans. They live in fresh water as well as brackish water. The ones we saw are clearly fresh water species and live in the sediments at the bottom of container # 14.

What do they eat? Well, ostracods can be herbivores (eating algae or weeds), carnivores (eating protozoans and even bigger prey when they attack in groups), scavengers (feeding on dead plant and animal material) and filter feeders. They play an important role in the food web (feeding connections, what-eats-what) since they are a food source for many species of fish.

Ecological importance: The cool thing about ostracods is that they can be used to determine the water quality of ponds and lakes. There seem to be a lot of different kinds of ostracods when water is polluted with chemicals such as phosphates, sulfates, chlorine and nitrates while you will see more ostracods of the same kind in less polluted water.

Cool facts! Ostracods living in the coastal waters of Japan, Caribbean and Australia can produce a blue light by a process called bioluminescence (light produced by a living organism).

These bioluminescent ostracods are called Cypridina and are also known as “blue tears” or “blue light.” Japanese soldiers collected these ostracods, dried them and pulverized them into powder. By adding ocean water to this powder, they were able to produce enough light to read their maps or orders from their superiors without being seen by the enemy.

Ostracods are tough creatures and can sometimes survive being eaten by fish! Others can survive being out of the water by taking up small amounts of water in their shell. Because their shells preserve so well, ostracods are the oldest preserved crustaceans in fossil records!

Take a closer look at the specimen we found…do you see the eyes??

ostracod with eyes labeled


2 Comments leave one →
  1. permalink
    July 9, 2014 4:08 pm

    This I will show to Natalie, she would love it. As long as it is not one her it is great. 

    • July 9, 2014 4:38 pm

      I am so glad! And if I come across anything on carnivorous plants, I will let you know! 🙂

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