Inside the eye of a Daphnia – this common fresh water flea (France)

By using a plankton net in a river, it becomes easy to collect an incredible things. Luckily, we got a lot of Daphnia, this small planktonic crustacean was omnipresent in our sample.

Overview of a Daphnia (source : https://en.wikipedia.org/wiki/Daphnia )

This organism have been well studied as model in biology since its transparency is giving the possibility to see its different organs. From 1–5 millimetres long, Daphnia appears very nicely under a foldscope.

On this video we can clearly see its compound eye, its heart betting super fast, the whole structure of its gut and even a smaller Daphnia that was present inside this bigger one a minute before. It’s interesting to learn that :

Most Daphnia species have a life cycle based on “cyclical parthenogenesis”, alternating between parthenogenetic (asexual) reproduction and sexual reproduction. For most of the growth season, females reproduce asexually.


This organism is a filter feeders because capable of creating a current by beating their legs to bring material into their digestive tract and ingesting mainly unicellular algae that are even visible inside its gut in this video.

The nervous system is characterized by the cerebral ganglion, which is located close to the gut and near the eye. Juvenile and adult Daphnia have one large compound eye, whereas embryos show two brownish eye spots that fuse during the last part of the development. The compound eye helps to orient the animal while swimming. A small structure called a naupliar eye is located between the mouth and the compound eye on top of the cerebral ganglion.

The naupliar eye is generally a single median eye comprising three- or four-pigment cup ocelli, sometimes with a lens, probably enabling the organism to determine the direction of a source of light for orientation. The median eye is typical of crustacean nauplius larvae. It may degenerate as the larva develops, or it may persist into the adult form.

It’s then easy to understand why this eye is capable of a small spinning orienting the visible pigment cup ocelli in the intermediate position to capture the direction of the light more accurately.

Sources :

Ecology, Epidemiology, and Evolution of Parasitism in Daphnia https://www.ncbi.nlm.nih.gov/books/NBK2042/

Wikipedia :
https://en.wikipedia.org/wiki/Daphnia

Encyclopedia : https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/nauplius-eye

4 Comments Add yours

  1. MananSuri says:

    This is such an amazing post! The clarity of the slides in this as well as your previous posts is very insightful to the structure and functioning of Daphnia.
    As far as I have read, Daphnia lay eggs, so maybe what you saw inside the larger Daphnia might have been it’s organs.
    I have also been experimenting with making slides of water fleas, but I faced a problem as the fleas got crushed very often on the slide, so do you have any tips on that or perhaps you can share how you made the slide… 🙂

  2. tpollina says:

    Thank you very much @Manansuri !
    The mounting was super simple ! Because I was surrounded by kids, I used transparent tape on a glass slide. Instead of trying to remove the maximum of water, I just let some water around the Daphnia by creating a chamber with the tape. I can post on that simple technique if you don’t understand me 😉 !

    1. MananSuri says:

      Wow that sounds quite interesting and useful . Would really appreciate if you made a post about it. Thank you so much!!

  3. tpollina says:

    Okay Manansuri, I will make that today 😉

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