Pentacrinoidea is a subclass of

crinoid 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 ...

s containing all members of Crinoidea except for the exclusively

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

camerates (subclass Camerata). It was originally named in 1918 by Otto Jaekel, who hypothesized a fundamental split between camerate and non-camerate crinoids. Later workers doubted this interpretation, and Pentacrinoidea was rarely used during the rest of the 20th century. Recent

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 ...

work has provided strong support for Jaekel's hypothesis, and Pentacrinoidea was reinstated in a 2017 revision of crinoid systematics. Pentacrinoidea includes most major crinoid groups, such as the living Articulata and extinct Flexibilia (together forming the parvclass

Cladida Cladida is a major subgroup of crinoids with a complicated taxonomic history. Cladida was originally applied to a wide assortment of extinct crinoids with a dicyclcic calyx. Under this original definition, cladids would represent a paraphyletic ...

) as well as the extinct Disparida. It is a

stem-based taxon Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a '' type'', which ...

, defined as including all crinoids closer to ''

Pentacrinites ''Pentacrinites'' is an extinct genus of crinoids that lived from the Hettangian to the Bathonian of Asia, Europe, North America, and New Zealand. Their stems are pentagonal to star-shaped in cross-section and are the most commonly preserved par ...

'' (a

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

articulate) or '' Apektocrinus'' (an

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. ...

cladid) than to '' Rhodocrinites'' or '' Actinocrinites'' (which are camerates). Pentacrinoidea incorporates a node-based equivalent, Inadunata, which includes all descendents of the last common ancestor between '' Synbathocrinus'' (a representative disparid) and '' Dendrocrinus'' (a representative cladid).

References

Crinoidea Early Ordovician first appearances {{paleo-crinoidea-stub