Isocrinidae

Japanese sea lily Metacrinus rotundus, from the Natural History Museum.

Belongs within: Articulata.

The Isocrinidae are a group of stalked crinoids known from the Triassic to the present day. Members of this group have small central cups and arms that generally divide into equal branches.

Characters (from Wienberg Rasmussen 1978): Cup rather small, low, cryptodicyclic. Small, concealed infrabasals present in some genera. Basals rather small, exposed, separated on surface by lower point of radials or united as low basal circlet. Radials larger, without distinct median prolongation of lower edge to cover uppermost columnals. Radial articular face for arms large, muscular, with distinct muscular and ligament fossae. Arms divided at primibrachs 2 except in Metacrinus, where first division may vary from primibrachs 4 to primibrachs 7. Further divisions found in most genera, but generally few, up to quartaxil, or in Endoxocrinus up to sixth division. Divisions usually more or less isotomous, with minor variations such as absence of distal divisions in inner branches present in some genera (all divisions endotomous, with inner branches remaining undivided, in Endoxocrinus). Increase in number of brachial divisions by augmentative regeneration found in Endoxocrinus and Teliocrinus. Cryptosyzygy generally present at primibrachs 1-2 and more distal, may be replaced by synarthry in brachials 1-2 and by symmorphy in more distal articulations. Synarthrial articulations, when present, may vary from almost flat to deeply embayed, concavity facing distally. Pinnulation complete, all pinnules free. Tegmen low.
Column pentalobate or pentagonal to circular in section. Proximal columnals pentalobate, alternating, with radial pores in sutures. Nodals with circular to transverse elliptical cirrus sockets, commonly with distinct fulcral ridge. Cirrus sockets five or less in each nodal placed on side, in some genera near to upper or lower edge. Columnal articulations symplectial with distinct crenulae along edge and adradial, forming a petaloid pattern. Petals never extremely narrow or separated by large radial spaces. Internodal length varying from one or two internodals in a species of Endoxocrinus to more than 30 in Isselicrinus.

<==Isocrinidae
    |--Teliocrinus Döderlein 1912 [incl. Comastrocrinus Clark 1912] WR78
    |    `--T. springeri (Clark 1909) (see below for synonymy) WR78
    |--Doreckicrinus Rasmussen 1961 WR78
    |    `--*D. miliaris (Nielsen 1913) [=Pentacrinus miliaris] WR78
    |--Annacrinus Clark 1923 WR78
    |    `--*A. wyvillethomsoni (Jeffreys ex Thomson 1872) [=Pentacrinus wyvillethomsoni] WR78
    |--Cenocrinus Thomson 1864 WR78
    |    `--*C. asterius (Linnaeus 1767) (see below for synonymy) WR78
    |--Chariocrinus Hess 1972 WR78
    |    `--*C. andreae (Desor 1845) [=Isocrinus andreae] WR78
    |--Hypalocrinus Clark 1908 WR78
    |    `--*H. naresianus (Carpenter 1882) [=Pentacrinus naresianus] WR78
    |--Carpenterocrinus Clark 1908 (n. d.) WR78
    |    `--*C. mollis (Carpenter 1884) [=Pentacrinus mollis] WR78
    |--Tauriniocrinus Rovereto 1939 (n. d.) WR78
    |    `--*T. gastaldi (Michelotti 1847) [=Pentacrinus gastaldi] WR78
    |--Cainocrinus Forbes 1852 [incl. Picteticrinus de Loriol in de Loriol & Pellat 1875 non Étallon 1857 (n. n.)] WR78
    |    |--*C. tintinnabulum Forbes 1852 WR78
    |    `--C. beaugrandi (de Loriol in de Loriol & Pellat 1875) [=Picteticrinus beaugrandi] WR78
    |--Balanocrinus Agassiz in Desor 1845 WR78
    |    |--*B. subteres (Münster in Goldfuss 1831) [=Pentacrinites subteres] WR78
    |    `--B. pentagonalis WR78
    |--Chladocrinus Agassiz 1836 [incl. Polycerus Fischer von Waldheim 1811] WR78
    |    `--*C. basaltiformis (Miller 1821) WR78 (see below for synonymy)
    |--Neocrinus Thomson 1864 WR78
    |    `--*N. decorus Thomson 1864 WR78, A96, WR78 [=Pentacrinus (*Neocrinus) decorus WR78]
    |--Nielsenicrinus Rasmussen 1961 WR78
    |    |--*N. obsoletus (Nielsen 1913) [=Pentacrinus obsoletus] WR78
    |    |--N. chavannesi WR78
    |    `--N. fionicus WR78
    |--Endoxocrinus Clark 1908 [incl. Diplocrinus Döderlein 1912] WR78
    |    |--*E. parrae Gervais 1835 WR78
    |    |--E. alternicirrus (Carpenter 1884) WR78 [=Diplocrinus alternicirrus C50]
    |    `--E. maclearanus (Thomson 1877) [=Pentacrinus maclearanus, Isocrinus (*Diplocrinus) maclearanus] WR78
    |--Isselicrinus Rovereto 1914 [incl. Lipocrinus Rasmussen 1953] WR78
    |    |--‘Pentacrinus’ didactylus (d’Archiac 1846) [incl. *Isselicrinus insculptus Rovereto 1914] WR78
    |    |--I. paucicirrhus WR78
    |    `--I. subbasaltiformis (Miller 1821) [=Pentacrinites subbasaltiformis, *Lipocrinus subbasaltiformis] WR78
    |--Austinocrinus de Loriol 1889 [incl. Penroseocrinus Sieverts-Doreck 1953] WR78
    |    |--A. erckerti (Dames 1885) (see below for synonymy) WR78
    |    |--A. mexicanus (Springer 1922) [=Balanocrinus mexicanus, A. (*Penroseocrinus) mexicanus] WR78
    |    `--A. rothpletzi Stolley 1892 WR78
    |--Metacrinus Carpenter 1882 [incl. Saracrinus Clark 1923] WR78
    |    |--*M. wyvillei Carpenter 1884 WR78
    |    |--M. angulatus WR78
    |    |--M. fossilis AB01
    |    |--M. nobilis Carpenter 1884 [=*Saracrinus nobilis] WR78
    |    `--M. rotundus (Carpenter 1884) LR06
    `--Isocrinus von Meyer in Agassiz 1836 [=Isocrinites von Meyer 1836] WR78
         |--*I. pendulus (von Meyer 1836) (see below for synonymy) WR78
         |--I. australis [incl. I. australis var. albascopularis] F71
         |--I. blakei (Carpenter 1882) [=Pentacrinus blakei, Neocrinus blakei] WR78
         |--I. candelabrum WR78
         |--I. cingulatus U78
         |--I. gravinae Bather 1918 WR78
         |--I. hercuniae U78
         |--I. scipio WR78
         `--I. tyrolensis WR78
              |--I. t. tyrolensis U78
              `--I. t. major U78

Austinocrinus erckerti (Dames 1885) [=Pentacrinus erckerti; incl. *A. komaroffi de Loriol 1889, P. sulcifer Eichwald 1871 (n. d.)] WR78

*Cenocrinus asterius (Linnaeus 1767) [=Isis asteria, Polycerus asterius; incl. Encrinus caputmedusae Lamarck 1816] WR78

*Chladocrinus basaltiformis (Miller 1821) WR78 [=Pentacrinites basaltiformis WR78; incl. *Polycerus stoloniferus Fischer von Waldheim 1811 J78, WR78]

*Isocrinus pendulus (von Meyer 1836) [=*Isocrinites pendulus; incl. Pentacrinus amblyscalaris Thurmann in Thurmann & Étallon 1862] WR78

Teliocrinus springeri (Clark 1909) [=Hypalocrinus springeri, *Comastrocrinus springeri; incl. *Teliocrinus asper Döderlein 1912] WR78

*Type species of generic name indicated

REFERENCES

[AB01] Aronson, R. B., & D. B. Blake. 2001. Global climate change and the origin of modern benthic communities in Antarctica. American Zoologist 41: 27-39.

[A96] Ausich, W. I. 1996. Crinoid plate circlet homologies. Journal of Paleontology 70: 955-964.

[C50] Clark, A. H. 1950. A monograph of the existing crinoids. Vol. 1. The comatulids. Part 4c. Superfamily Tropiometrida (the families Thalassometridae and Charitometridae). Bulletin of the United States National Museum 82 vol. 1 (4c): 1-383.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1-167.

[J78] Jeffords, R. M. 1978. Dissociated crinoid skeletal elements. In Treatise on Invertebrate Paleontology pt. T. Echinodermata 2. Crinoidea (R. C. Moore & C. Teichert, eds) vol. 3 pp. T928-T937. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[LR06] Lanterbecq, D., G. W. Rouse, M. C. Milinkovitch & I. Eeckhaut. 2006. Molecular phylogenetic analyses indicate multiple independent emergences of parasitism in Myzostomida (Protostomia). Systematic Biology 55 (2): 208-227.

[U78] Ubaghs, G. 1978. Skeletal morphology of fossil crinoids. In Treatise on Invertebrate Paleontology pt. T. Echinodermata 2. Crinoidea (R. C. Moore & C. Teichert, eds) vol. 1 pp. T58-T216. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[WR78] Wienberg Rasmussen, H. 1978. Articulata. In Treatise on Invertebrate Paleontology pt. T. Echinodermata 2. Crinoidea (R. C. Moore & C. Teichert, eds) vol. 3 pp. T813-T927. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).