Pentacrinoidea is a subclass of

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

s containing all members of Crinoidea except for the exclusively

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

camerates (subclass Camerata). It was originally named in 1918 by

Otto Jaekel Otto Max Johannes Jaekel (21 February 1863 – 6 March 1929) was a German paleontologist and geologist. Biography Jaekel was born in Nowa Sól, Neusalz (Nowa Sól), Prussian Silesia, the son of a builder and the youngest of seven children. He st ...

, 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 () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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) as well as the extinct

Disparida Disparida is an parvclass of extinct marine animals in the class Crinoidea. Disparids are a speciose and morphologically diverse group of crinoids distinguished by their monocyclic calyx and slender arms without pinnules. They range from the Ear ...

. It is a

stem-based taxon Phylogenetic nomenclature is a method of nomenclature for taxon, taxa in biology that uses phylogenetics, phylogenetic definitions for taxon names as explained below. This contrasts with Biological classification, the traditional method, by which ...

, defined as including all crinoids closer to '' Pentacrinites'' (a

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

articulate) or '' Apektocrinus'' (an

Early Ordovician The Early Ordovician is the first epoch (geology), epoch of the Ordovician period, corresponding to the Lower Ordovician series (stratigraphy), series of the Ordovician system. It began after the Cambrian Stage 10, Age 10 of the Furongian epoch o ...

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

References

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