|WikiProject Arthropods||(Rated Start-class, Mid-importance)|
It is believed that they may have evolved from the trilobites or annelids (segmented worms), and that they themselves are the ancestors of the Arachnida (spiders).
I dropped this. Very few believe that the Merostomata themselves gave rise to the Arachnids, only that their ancestors are related, which is given away by the two making up the Chelicerata. The same comment applies to the relationship between the Merostomata and trilobites, and all arthropods are typically supposed to have arisen one way or another from annelids.
Merostomata is no longer considered a proper phylogenetic grouping for Horseshoe crabs. one source for this is http://tolweb.org/Arthropoda/2469 . Xiphosura is now used in place of Merostomata. this page is what should be used if trying to discuss Horseshoe crabs, I think http://en.wikipedia.org/wiki/Xiphosura Swilk 04:15, 24 November 2006 (UTC)
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