Remoras, or shark suckers, are a family of eight species of tropical fish that for more than a millennium have inspired a mythology that is almost stranger than those odd little hats they've got on. The hats are sucking disks that remoras use to latch onto pretty much anything for a free ride, whether it is other fishes, turtles, divers or ships.

Now scientists have figured out where the shark sucker's sucking disks actually came from. In a study published in the December 2012 Journal of Morphology, ichthyologists (fish experts) injected red dye into the bones of larval remoras and other fishes so they could watch them grow. Up to a certain point, the dorsal fin and supporting skeleton appeared to develop in the same way in both kinds of fishes. Then the remora's dorsal fin bones expanded and shifted forward toward the fish's head. By the time the juvenile remora had grown to 30 millimeters long, it had a two-millimeter-long, perfectly formed sucking disk.

This article was originally published with the title What Is It?.

4 Comments

1. 1. louvar 02:49 PM 3/21/13

   Hi Becky,
   I am one of the co-authors of this paper. Just to clarify, we did not "inject live specimens with red dye so we could watch them grow." This would be extremely difficult, if not impossible. We worked with preserved specimens from museum collections. After selecting as complete a developmental series as we could get, we used the process known as clearing and staining, in which formalin-fixed, alcohol-preserved specimens are stained for cartilage (alcian blue) and bone (alizarin red). The muscle and most other soft tissue is digested with trypsin, a proteinaceous enzyme and the specimen is finally cleared in a glycerine solution.
   From the paper (http://onlinelibrary.wiley.com/doi/10.1002/jmor.v273.12/issuetoc):
   "All specimens, except where noted, were cleared and doublestained(c&s) according to Taylor and van Dyke (1985) and were observed with a Zeiss Discovery V12 or V20 stereomicroscope. Our ontogenetic study is based on developmental stages of three different species of the echeneid genus Remora, because we did not have a complete ontogenetic series of any echeneid species. This has no effect on our homology propositions, as the
   homology issues we address are identical for all species of Remora and even echeneids.
   Cheers,
   Dave
   G. David Johnson
   Curator/Ichthyologist
   Division of Fishes
   National Museum of Natural History
   

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2. 2. The Ethical Skeptic 01:44 AM 3/24/13

   Well done bit of research David, and still a great article for us laymen Becky. Very interesting and informative, demonstrating evolution's preference for altered expression of existing morphologies over emergence of new distinct feature morphologies. This as much an outcome of probable nature employing most-like elements. Yet still ends with an elegant progression. Fascinating!
   
   - TES

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3. 3. Stuka1944 09:55 AM 3/24/13

   Thanks for the clarification Dave. As far as the original article...very unsatisfying. The title led me to believe the article would delve into the evolutionary advantages to the sucker, not basically "bones shifted and ta-da, a sucker"
   
   Of course I'm not trying to downplay the value of the research, the article is just unclear and lacking any real detail.

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4. 4. roese 12:31 PM 3/26/13

   Check out Becky's original post for more detail: http://blogs.scientificamerican.com/running-ponies/2013/02/04/how-the-sharksucker-got-its-suction-disc/

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