Excellent question! They can’t.
I should not have said genetic, I should have said phylogenetic. The analyses I was talking about use morphological characters in leiu of DNA.
Thank you for calling me out - I have corrected the post!
No - I think they are usually considered sister groups, instead. It’s also debated as to whether eurypterids are more closely related to horseshoe crabs or arachnids.
If they are sister groups, wouldn’t that still leave them as stem-horseshoe crabs in the wider sense?
To further elaborate after a bit more reading…
If eurypterids and horseshoe crabs are more closely related to each other than they are to the rest of the chelicerates (Merostomata), then yes, eurypterids would be considered stem-horseshoe crabs. It’s common to still see this theory floating around.
However, phylogenetic analyses now suggest that Merostomata is an unnatural grouping, and that eurypterids are more closely related to arachnids than to horseshoe crabs (e.g. Lamsdell et al. 2015).
TBH… no…
I have been more of a journal reader than a book reader, but I am in the process of trying to change that. So if I come across anything I will be sure to share it!
Do any other followers have any recommendations?
I’ve not heard that before. Maybe they used to?
A quick google scholar search seems to suggest most molecular analyses agree they are of the class or closely related to the class maxillopoda.
No - I think they are usually considered sister groups, instead. It’s also debated as to whether eurypterids are more closely related to horseshoe crabs or arachnids.
This is such a great idea! Absolutely!!
Of course!
Synapta maculata - also known as the snake cucumber. Despite looking like a snake, it is in fact a giant (or at least very long) sea cucumber. It can grow up to 3 meters long and lives in the Indo-Pacific Ocean. Sea cucumbers are pretty famous for ejecting their internal organs to scare off or distract predators, however S. maculata instead just splits in two and re-grows the rest of its body at a later date.
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Image Credit: NOAA 2010
They are a subclass of parasitic crustaceans also known as “tongue worms” because they all look a lot like worms and a few of them kinda look like tongues. Their formal name (pentastomida) comes from their five appendages - one of which is actually a mouth and the other four are hooks that they use to cling to the respiratory tracts of their vertebrate hosts.
Like other crustaceans, they are chitinous - so even thought they might look kinda squishy, they aren’t (at least I don’t think they are, I haven’t touched one). They are in the class Maxillopoda along with copepods (think Plankton from Spongebob) and barnacles.
Titanomyrma - a Paleogene ant the size of a hummingbird. Well, the queen could grow to the size of a hummingbird, i.e. around 6 cm. Worker ants of this genus are yet to be discovered in full. Members of this genus have been found in the Green River Formation in Wyoming and the Messel Shales of Germany.
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Image Credit: U. Kiel 2011
