Dekatriata is a clade of planatergan chelicerates including the groups Arachnida, Chasmataspidida, Eurypterida[1] and additionally two stem-genera Winneshiekia and Houia.

[2] Dekatriata is defined by an opisthosoma with 13 segments as groundplan (the number proposed to be secondarily reduced in most arachnid orders[1]) and fused, plate-like appendages on the first opisthosomal segment (somite VII).

[1]

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