The disparids: Weird and weedy crinoids of the Palaeozoic

Stephen K Donovan (Netherlands) and David N Lewis (UK) Palaeozoic crinoids are uniformly beautiful and come in many shapes and sizes, but almost all fall into one of three principal groups. The camerates are the largest and most robust, commonly incorporating the lower part of the arms into an enlarged cup with a plated roof (tegmen), producing a structure that is commonly reminiscent of a golf ball. The cup may be monocyclic (one circlet of basal plates supporting the radials; see Glossary (below) for explanation of specialist terms) or dicyclic (two basal circlets, that is, infrabasals and basals, supporting the radials). The arms of camerate crinoids bear multiple, fine branchlets called pinnules that must have formed an efficient ‘net’ for feeding on plankton. The second major group, the cladids (plus the closely related flexibles) are dicyclic, lack an armoured tegmen and, except for some advanced (Upper Palaeozoic) forms, lack pinnules. The flexibles may also show a camerate-like feature with small plates separating the arms. And then there are the disparids. The disparids were the ‘weeds’ of the Palaeozoic crinoids; generally smaller and less impressive than other crinoids, but including some unusual, even bizarre forms. Herein, we introduce the disparids of the British Palaeozoic, examining their form and function, and where to collect them. The disparid cup was commonly small, always monocyclic and lacked an armoured tegmen, but had a prominent anal sac or tube in some groups. The arms were usually slender, lacked pinnules and were branched or unbranched, and … Read More

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