Horseshoe crabs are really relatives of spiders, scorpions


There were several different branches of arthropods that ascended from the waters and became ground loving “bugs”.

Insects is just the group with SIX legs.

“It might not surprise you that both scorpions and lobsters are in the same Phylum Arthropoda. … The anatomy of a scorpion has some similar characteristics to other arthropods, such as lobsters and crabs. They also have similar features to spiders and other arachnids.”

Horseshoe crabs survive from the Cambrian age of trilobites!

“Fossils of these first arthropods can be found in rock dating to the Cambrian period, which began 545 million years ago . They included trilobites, horseshoe crabs, and crustaceans. Centipedes, millipedes, and scorpions were among the first arthropods to reach dry land.”

Of the major branch of the arthropods “called Uniramia,
there are the Hexapoda (insects),
and there are the Myriapoda (centipedes and millipedes)…”

Of the major branch of the arthropods called Chelicerata
there are the sea spiders, and
[arachnids] (Arachnid - Wikipedia) (including scorpions, spiders,
and probably horseshoe crabs.

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“”"A new fossil discovery in Britain captures a previously unseen stage in the evolution of these ancient arthropods—the transformation of two-branched legs into nearly identical but separately attached limbs, one of which was destined 'to disappear.

“This fossil provides remarkable confirmation of ‘the loss of a limb branch’ during horseshoe crab evolution, a change predicted by the common presence of two branches in the arthropods that appeared earlier, during the Cambrian explosion,” said Derek E. G. Briggs, director of the Yale Peabody Museum of Natural History and lead author of a paper to be published online the week of Sept. 10 in the journal PNAS.

The fossil dates from the Silurian period, about 425 million years ago."""

“”'loss of outer rami following the separation of the rami could result from repression and/or loss of appendage-patterning gene domains,"""
“”“The appearance of the biramous limb likely predates the split of these major clades. The appendage morphology in the less well preserved Burgess Shale arthropod Sanctacaris (23) shows similarities to that in Dibasterium and Offacolus (8), but the origin of the biramous limb within early Paleozoic arthropods remains to be elucidated.”""

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The interesting thing about the new finding is that it implies that horseshoe crabs might have had land-living ancestors and returned to the water. The other possibility would be multiple, independent moves to land within arachnids.

As do all animals, right? No, there are no Cambrian fossils of horseshoe crabs. The oldest horseshoe crab fossils are Ordovician.

Uniramia doesn’t exist. Insects are derived crustaceans.

On the matter of Uniramia, I stand corrected. @John_Harshman, did insects become six-legged while still in the water, or after arriving on land?

As for horseshoe crabs, I also stand corrected… though I was very close, with a 7% margin of error.

Horseshoe crabs came 35 million years after the close of the Cambrian… but, John, you were remiss in not pointing out that Horseshoes and trilobites did share the oceans together, since triolobites did not go extinct until the end of the Permean … about 252 million years ago… and the dawn of the Triassic Period.

"Ordovician trilobites were successful at exploiting new environments, notably reefs. The Ordovician mass extinction did not leave the trilobites unscathed; some distinctive and previously successful forms such as the Telephinidae and Agnostida became extinct. The Ordovician marks the last great diversification period amongst the trilobites: very few entirely new patterns of organisation arose post-Ordovician. Later evolution in trilobites was largely a matter of variations upon the Ordovician themes.

We don’t know. There are no six-legged marine fossils on the insect line, nor are there any multi-legged terrestrial ones.

Didn’t know that was being questioned.

Creationism always should welcome squezzing critters into KINDS. So if these creatures are related with others well its fine.
Yet the problem in all this is there is no evidence except a FAITH that dna is a trail.
Thats just a guess. If its a common design with a closed system then like dna would be in like morphological creatures who otherwise are unrelated. for example man has ;like dna with apes but thats just a sign of like morphology. Not a sign of a common descent trail.
evolutionists do a poor job of science when they rule out, at the gate, the option that dna is just a manipulation of dna itself.
In other words they PRESUME only a common descent option.
Thus another reason evolutionism is not a scientific investigation or rather its just a untested hypothesis.