''Promachocrinus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of free-swimming, stemless

crinoids 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 ...

. It was a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

genus, with the only species in the genus being ''

Promachocrinus kerguelensis ''Promachocrinus kerguelensis'' is a species of free-swimming, stemless crinoids. It was the only member of its genus until several species were discovered in 2023. ''P. keruguelensis'' a coldwater crinoid which is found in the seas around Antarc ...

,'' until the discovery of four new species, establishment of two others previously described and the transfer of another species to the genus in 2023. Known for being coldwater crinoids, members of ''Promachocrinus'' are typically found in the seas around

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

and surrounding island groups, including under the

sea ice Sea ice arises as seawater freezes. Because ice is less density, dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world' ...

. Previously known for having 20 arms, two of the species now included in the genus have 10 arms. Many of the species are circum-Antarctic and can be difficult to tell apart without DNA sequencing.

Species

There are eight accepted species of ''Promachocrinus'' as of August 2023: * ''

Promachocrinus fragarius ''Promachocrinus fragarius'', commonly known as the Antarctic strawberry feather star, is a species of stemless, free-swimming crinoid. It was one of several new species of ''Promachocrinus'' to be described in 2023. The discovery of the species ...

'' McLaughlin, Wilson and Rouse 2023 * ''

Promachocrinus joubini ''Promachocrinus'' is a genus of free-swimming, stemless crinoids. It was a monotypic genus, with the only species in the genus being '' Promachocrinus kerguelensis,'' until the discovery of four new species, establishment of two others previousl ...

'' Vaney, 1910 * ''

'' Carpenter, 1879; Type species * ''

Promachocrinus mawsoni ''Promachocrinus'' is a genus of free-swimming, stemless Crinoid, crinoids. It was a Monotypic taxon, monotypic genus, with the only species in the genus being ''Promachocrinus kerguelensis,'' until the discovery of four new species, establishmen ...

'' (Clark, 1937) * ''

Promachocrinus unruhi ''Promachocrinus'' is a genus of free-swimming, stemless crinoids. It was a monotypic genus, with the only species in the genus being '' Promachocrinus kerguelensis,'' until the discovery of four new species, establishment of two others previousl ...

'' McLaughlin, Wilson and Rouse 2023 * ''

Promachocrinus uskglassi ''Promachocrinus'' is a genus of free-swimming, stemless crinoids. It was a monotypic genus, with the only species in the genus being '' Promachocrinus kerguelensis,'' until the discovery of four new species, establishment of two others previousl ...

'' McLaughlin, Wilson and Rouse 2023 * ''

Promachocrinus vanhoeffenianus ''Promachocrinus'' is a genus of free-swimming, stemless crinoids. It was a monotypic genus, with the only species in the genus being '' Promachocrinus kerguelensis,'' until the discovery of four new species, establishment of two others previousl ...

'' Minckert, 1905 * ''

Promachocrinus wattsorum ''Promachocrinus'' is a genus of free-swimming, stemless crinoids. It was a monotypic genus, with the only species in the genus being '' Promachocrinus kerguelensis,'' until the discovery of four new species, establishment of two others previousl ...

'' McLaughlin, Wilson and Rouse 2023

References

Antedonidae Crinoid genera Marine fauna of Antarctica {{improve categories, date=August 2023