Random Questions (Tardigrades, Trilobites, Lungfish)

Okay, I’m putting together some zoology resources and I am having a hard time finding some specific, odd facts. Perhaps those with more knowledge can help me out?

  1. Do tardigrades have exoskeletons? I see a lot of talk about water bears having a chitinous cuticle, but I can’t quite tell if a cuticle is the same thing as an exoskeleton, or if an exoskeleton needs an extra layer on top of he cuticle.

  2. Did trilobites have mandibles? I know centipedes, millipedes, crustaceans, and insects have mandibles. Chelicerates do not have mandibles. Did trilobites have mandibles?

  3. Do lobe-finned fish (lungfish / coelacanth) have 2-chambered hearts, or 3-chambered hearts? I see a lot of sources say that “fish have 2-chambered hearts and amphibians have 3-chambered hearts” but because lungfish are closer phylogenetically to amphibians, I just wanted to be sure.

  4. Can lampreys see Red-Green-Blue-UV light? It seems that teleost fish can see this spectrum, and I’m trying to figure out if this tetrachromacy exists in jawless fish to.

Thanks for considering this random assortment of questions :laughing:


According to Google, the definition for exoskeleton is, “a rigid external covering for the body in some invertebrate animals, especially arthropods, providing both support and protection.” By that definition, I’d assume the cuticle of a tardigrade does the same job? Personally, I’d say that exoskeleton is more of a blanket-term for the tough covering in an invertebrate.

Trilobites did not have the mandibles, unlike many arthropods. Due to this, they were restricted to softer foods, such as soft-bodies invertebrates and bits of detritus on the sea floor.

Lungfish have three-chambered hearts, like amphibians, since their atria is divided through a septum. I couldn’t find a picture of a coelacanth heart, but I would imagine it works pretty much the same.

Don’t quote me on it, but I think lampreys do sense this spectrum. Lampreys have well-developed eyes. They also have extra ocular photoreceptors. These receptors sense blue-green light especially well. It’s also been found that they can detect UV light as well.

If you see anything wrong with this, please tell me. Hopefully this helps!


Vertebrates can also have exoskeletons. Gnathostome fish for example, are described as having both endo- and exoskeletons. The definition of exoskeleton is not hard and fast, but people who study tardigrades generally refer to their cuticle. The phrase “tardigrade cuticle” gets 146 hits on Google Scholar, while the phrase “tardigrade exoskeleton” gets only eight.


I should’ve said this, but take my information with a grain of salt since I’m no biologist. Thanks for the correction!

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