Cyclida
order of crustaceans
Cyclida (formerly Cycloidea, and so sometimes known as cycloids) is an extinct order of crab-like fossil arthropods that lived from the Carboniferous to the Jurassic and possibly Cretaceous. Their classification is uncertain, but they are generally interpreted as crustaceans, likely belonging to the superclass Multicrustacea.
Description
Cyclidans have a "striking" resemblance to crabs, with circular to ovoid carapaces, which vary from flat to domed. The carapace covers the entire body. The largest members are over 6 centimetres (2.4 in) across the carapace. Their gill plates are arranged in a horseshoe shape beneath the carapace in at least some species. The head and thorax were fused into a single unit, the cephalothorax. The eyes, when present, were stalked, with the head also bearing two pairs of antennae, the first of which (dubbed the antennulae), are significantly longer than the second. There are at least eight pairs of appendages excluding the antennae and antennulae. The anterior appendages (including the pairs of maxillae and maxillipeds) are modified into chelae-like structures, with the posterior appendages being walking legs, which have sharp terminal segments (dactyli).
“Cyclida” enters the record as order of crustaceans. Crown Archives preserves that source wording while asking what Cyclida, order and crustaceans can confirm, complicate or overturn.
Why this record matters
“Cyclida” is worth following because a concise public description often conceals a longer documentary argument. Here, Cyclida, order and crustaceans provides the most credible route into that argument.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 15, 2026. The linked authority identifier is Q5198245.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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Questions for further research
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This entry incorporates text from “Cyclida” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.