this is my first time posting here. I was in my Zoology lab doing a dissection on a Crayfish when I noticed these hairlike structures within the gills. They were very "snappy" and fine, and would break off if I pulled hard enough. I put some on a wet mount under a dissecting microscope, but my Lab prof and the parasitologist could not identify it. We put it under a compound microscope and thought maybe it is an animal but we couldn't definitively say it had no cell well. My profs thought it was an animal, with setae, but I would really like to know what it is

Edit here are the images:microscope image microscope image 2

  • $\begingroup$ Were the hair things coming off the central tubes paired? It almost looks like they are, but I'm not sure. $\endgroup$
    – Resonating
    Mar 19, 2015 at 3:01
  • $\begingroup$ I had to concede on this one after a lengthy query. If we had a look at either end of whatever it is it'd make identification a tad easier. $\endgroup$
    – CKM
    Mar 31, 2015 at 22:23

2 Answers 2


My best guess would be Trematoda which is a fluke worm that infects mollusk. I would think this is the larval stage of cercaria which is free swimming and develops in the mollusk and then moves on to infect others.

Here are some different images of a cercaria:



In this YouTube video you will see what is known as a "Rat King" which is just a ball essential of Trematoda. Here is a screenshot


  • $\begingroup$ It would be nice that the images from the question have some scale. The first picture of a trematode cercariae has a view of 0.267 mm across according to the source. From the average size of trematode cercaria, perhaps it's a little too small compared to the 'hair' structure on the (visible fine structures of) crayfish gills? $\endgroup$
    – SYK
    Mar 31, 2015 at 7:49
  • $\begingroup$ @SYK If you click edit, you will find the sources to the images. There was no scale provided. I just made do with what was available. The size of the rat king is appears to be an equivalent size. $\endgroup$
    – dustin
    Mar 31, 2015 at 13:58
  • $\begingroup$ @dustin OK, not that your image is not cool. I was just looking at the seemingly identical image at networlddirectory.com/blogs/permalinks/7-2006/… $\endgroup$
    – SYK
    Mar 31, 2015 at 18:58
  • $\begingroup$ I know this post received a bounty 4 years ago, but I really am not at all convinced this is a correct answer... $\endgroup$ Mar 13, 2019 at 3:00
  • $\begingroup$ @theforestecologist if you read the first sentence I wrote, I state it is a guess. With the available information giving, that was my best guess. $\endgroup$
    – dustin
    Mar 16, 2019 at 4:41

You asked this question 4 years ago, but i randomly noticed this only now. Whell, that not parasite, not Rat King or someting. This is "setobranchies" - crayfish's cleaning organ. They struggle when crayfish move his legs, and cleaning gills from dirt and sand. I hope this information may be usefull for you, even so many years later

  • 1
    $\begingroup$ Welcome to Biology.SE! Your answer is plausible, but you are much more likely to get a positive response if you explain why your identification is correct. Specifically, please edit your answer to add discussion of key features that led you to this conclusion and supporting references or at least validated images. Without this your answer is indistinguishable from opinion. ——— You may also wish to take the tour and then consult the help pages for additional advice on How to Answer effectively on this site. Thank you! 😊 $\endgroup$
    – tyersome
    Feb 13, 2020 at 17:31

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