Disparida is an

parvclass In biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, kingdo ...

of extinct marine animals in the class

Crinoidea Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...

. Disparids are a speciose and morphologically diverse group of crinoids distinguished by their monocyclic calyx and slender arms without pinnules. They range from the

Early Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

(

Tremadocian The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from to million years ago. The base of the Tremadocian is defined as the first appearance of the ...

) to

Middle Permian The Guadalupian is the second and middle series/epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± 0. ...

, reaching their highest diversity during the

Late Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

. While many disparids had a generalized shape typical of other stalked crinoids, some subgroups achieved strange forms. The long-lasting Calceocrinidae were recumbent forms, with a flattened crown bent back onto a stalk which rested on the seafloor. Other unusual disparid families include the armless Zophocrinidae, the spiral-armed Myelodactylidae, and the diminutive, simplified Pisocrinidae. Disparids have long been classified by the structure of their radial plates and different planes of symmetry, but a cumulative

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

approach has failed to confirm the validity of many proposed subgroups. Nevertheless, Disparida itself is well-supported as a distinct

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

group. Major traits of Disparida include: * Small monocyclic calyx, without interbasal plates. Radial plates are proportionally large and may be compound (with multiple components), while basal plates are often reduced. * Proximal branchial plates tend to fuse with their respective radials. * Thin, uniserial arms without pinnules. Branching is typically frequent. * Redevelopment of prominent bilateral symmetry via an axis aligned to one of the five rays making up the crown. This axis of symmetry may lie along the E ray (homocrinoid symmetry), D ray (heterocrinoid symmetry), C ray (isocrinoid symmetry), or A ray (crinoid/belemnocrinoid symmetry, which is developed to a lesser degree in other crinoids). * Posterior plates lie above the C radial.

List of families and genera

Disparida classification is undergoing revision. Many proposed families are

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...

. Family Acolocrinidae * Acolocrinus * Paracolocrinus Family Allagecrinidae * Allagecrinus * Isoallagecrinus * Kallimorphocrinus * Litocrinus * Metallagecrinus * Wrightocrinus Family Alphacrinidae * Alphacrinus Family Anamesocrinidae * Anamesocrinus Family Anomalocrinidae * Anomalocrinus * Geraocrinus Family Aptocrinidae * Othneiocrinus Family Athenacrinidae * Athenacrinus Family Belemnocrinidae * Belemnocrinus * Whiteocrinus Family Calceocrinidae * Anulocrinus * Calceocrinus * Catatonocrinus * Charactocrinus * Chirocrinus * Chiropinna * Corvucrinus * Cremacrinus * Cunctocrinus * Darraghcrinus * Deltacrinus * Diaphorocrinus * Dolerocrinus * Eohalysiocrinus * Epihalysiocrinus * Espanocrinus * Grypocrinus * Halysiocrinus * Minicrinus * Paracremacrinus * Senariocrinus * Stibarocrinus * Synchirocrinus * Trypherocrinus Family Catillocrinidae * Allocatillocrinus * Catillocrinus * Eucatillocrinus * Kolvacrinus * Isocatillocrinus * Metacatillocrinus * Mycocrinus * Neocatillocrinus * Notiocatillocrinus * Paracatillocrinus * Taucatillocrinus * Ufacrinus * Xenocatillocrinus Family Cincinnaticrinidae (i.e. Heterocrinidae, paraphyletic / polyphyletic) * Atyphocrinus * Cincinnaticrinus * Doliocrinus * Dystactocrinus * Glaucocrinus * Heterocrinus * Isotomocrinus * Ohiocrinus * Serendipocrinus * Tenuicrinus * Tryssocrinus Family Columbicrinidae * Columbicrinus * Praecursoricrinus Family Dulkumocrinidae * Dulkumocrinus Family Eustenocrinidae * Cataractocrinus * Coralcrinus * Eustenocrinus * Inyocrinus * Peniculocrinus * Pogonipocrinus * Virucrinus Family Haplocrinitidae * Haplocrinites Family Homocrinidae (paraphyletic / polyphyletic) * Apodasmocrinus * Bodacrinus * Cataraquicrinus * Daedalocrinus * Difficilicrinus * Drymocrinus * Ectenocrinus * Homocrinus * Ibexocrinus * Kastorcrinus * Penicillicrinus * Sygcaulocrinus * Tunguskocrinus Family Iocrinidae (paraphyletic) *

Caleidocrinus ''Caleidocrinus'' is a genus of sea lily that lived during the Middle and early Upper Ordovician in what is now the Czech Republic and Wales. References Iocrinidae Ordovician crinoids Fossils of Great Britain Fossils of the Czech Rep ...

* Grammocrinus * Iocrinus * Margoiocrinus * Muicrinus * Pariocrinus * Peltacrinus * Ristnacrinus * Schaldichocrinus * Tornatilicrinus * Westheadocrinus Family Maennilicrinidae * Heviacrinus * Maennilicrinus * Putilovocrinus * Vosekocrinus Family Myelodactylidae * Brachiocrinus * Crinobrachiatus * Eomyelodactylus * Herpetocrinus * Musicrinus * Myelodactylus Family Pisocrinidae * Cicerocrinus * Eocicerocrinus * Parapisocrinus * Pisocrinus * Playfordicrinus * Triacrinus * Trichocrinus Family Pygmaeocrinidae (polyphyletic) * Kroppocrinus * Pygmaeocrinus * Storthingocrinus Family Synbathocrinidae * Abyssocrinus * Phimocrinus * Ramacrinus * Stylocrinus * Synbathocrinus * Taidocrinus * Theloreus Family Tetragonocrinidae * Ramseyocrinus * Tetragonocrinus Family Zophocrinidae * Parazophocrinus * Tiaracrinus * Zophocrinus

Incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

* Agostocrinus? * Aureocrinus * Brutopisocrinus * Calcycanthocrinus * Changinocrinus * Claviculacrinus * Desmacriocrinus * Gongrocrinus * Heracrinus * Holynocrinus * Hypsocrinus * Jaekelicrinus * Junocrinus * Macnamaratylus * Paradoxocrinus * Perissocrinus * Perittocrinus? * Quiniocrinus * Regnellicrinus * Resetocrinus * Stereobrachicrinus * Tetracionocrinus? * Thaminocrinus * Trophocrinus * Xisoallegocrinus

References

Prehistoric crinoids {{paleo-crinoidea-stub