Bourgueticrinida is an order 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 that typically live deep in the ocean. Members of this order are attached to the seabed by a slender stalk and are known as sea lilies. While other groups of crinoids flourished during the Permian, bourgueticrinids along with other extant orders did not appear until the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

, following a mass extinction event in which nearly all crinoids died out.

Taxonomy

Bourgueticrinida has traditionally been viewed as an order of Articulata and a sister

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

to the order

Comatulida Comatulida is an order of crinoids. Members of this order are known as feather stars and mostly do not have a stalk as adults. The oral surface with the mouth is facing upwards and is surrounded by five, often divided rays with feathery pinnules. ...

, the feather stars. A study published in 2011 suggested that it should be renamed Bourgueticrinina and viewed as a suborder of Comatulida.

Characteristics

Sea lilies are crinoids with a calyx and five pairs of feather-like arms standing on a long stalk which is retained throughout the animal's life. This stalk is attached to the substrate by means of an enlarged, terminal disc or alternatively by means of several branching, irregular radicular cirri arising from the lowest part of the stem. Although these crinoids are usually

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

, they have been seen to drag themselves across the seabed with the help of their arms. The sea lilies are nearly all found at depths greater than although '' Metacrinus rotundus'' (a member of a different order) is found off the coast of Japan at a depth of only . The ossicles from which the stem is composed are known as columnals. They are discs with a circular, pentagonal, star-shaped or elliptical cross section. The stem is flexible and the columnals are connected to each other with ligaments. At each node where the columnals articulate with each other there may be a whorl of five cirri. These appendages are themselves formed of small ossicles called cirrals and the terminal one is often claw-like. These cirri provide additional anchorage if the stem happens to be in contact with the substrate.

Evolution

The earliest crinoid may have been '' Echmatocrinus'', the fossilised remains of which have been found in the

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fo ...

, but some authorities do not accept it as a crinoid. Bourgueticrinids first appeared in the fossil record during the

period, although other crinoid groups, now extinct, originated in the

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. T ...

. By the end of the Permian, crinoids were an abundant and very successful group and the columnals are plentiful in many fossiliferous

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

deposits. At that time there were over 6,000 species of sea lily but they were all but extinguished in the Permo-Triassic extinction event. It is believed that only one

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of sea lily survived that occurrence and that all modern crinoids, both the sea lilies and the feather stars, are descended from members of that genus. There are currently about 80 species of bourgueticrinids.

References

{{Taxonbar, from=Q4950171 Articulata (Crinoidea) Echinoderm orders Prehistoric animal orders Extant Triassic first appearances