Paracrinoidea

Reconstruction of Amygdalocystites florealis, from here.


Belongs within: Blastozoa.

The Paracrinoidea are a strictly Middle Ordovician group of stalked echinoderms with arms superficially like those of crinoids, but a central theca more similar to those of cystoids and other blastozoans.

Characters (from Kesling 1967): Calcareous plates encasing body constituting a theca, not differentiated into dorsal calyx and ventral tegmen; thecal plates variable in number, irregularly arranged, those of some species provided with pore structures in innner layer; theca invariably anchored by column of thin uniserial disc-shaped columnals. Ambulacral system made up of uniserial arms bearing uniserial pinnules. Arms may be free or attached on thecal surface, not more than four arms known in any species, although one or more arms may branch; ambulacral grooves covered by tiny plates, may not extend to ends of all pinnules. Hydropore present in some forms, not found in others; gonopore reported in some, not definitely established. Many forms with periproct opposite columnar facet and peristome offset to one side; periproct provided with anal pyramid.

<==Paracrinoidea [Deviata, Eustelea, Paracrinozoa]
    |  i. s.: Platycystites Miller 1889 [=Platycystis Bather 1900 non L├ęger 1892] K67
    |           |--*P. faberi Miller 1889 [=*Platycystis faberi] K67
    |           `--P. cristatus LS87
    |         Achradocystites von Volborth 1870 [=Achradocystis Haeckel 1896] K67
    |           `--*A. grewingkii von Volborth 1870 [=*Achradocystis grewingkii] K67
    |--Comarocystitidae [Brachiata, Comarocystidae] K67
    |    |--Billingsocystis Bassler 1950 K67
    |    |    `--*B. invaginata Bassler 1950 K67
    |    |--Schuchertocystis Bassler 1950 K67
    |    |    `--*S. radiata K67
    |    `--Comarocystites Billings 1854 [=Comarocystis Carpenter 1891] K67
    |         |--*C. punctatus Billings 1854 [=*Comarocystis punctata] K67
    |         |--C. obconicus K67
    |         `--C. shumardi K67
    `--Varicata K67
         |--Malocystitidae [Malocystidae] K67
         |    |--Malocystites Billings 1857 [=Malocystis Carpenter 1891] K67
         |    |    `--*M. murchisoni Billings 1857 [=*Malocystis murchisoni] K67
         |    `--Wellerocystis Foerste 1920 K67
         |         `--*W. kimmswickensis Foerste 1920 K67
         `--Amygdalocystitidae [Amygdalocystidae] K67
              |--Canadocystis Jaekel 1900 [incl. Sigmacystis Hudson 1911] K67
              |    |--*C. barrandei (Billings 1858) [=Malocystites barrandi] K67
              |    `--C. emmonsi (Hudson 1905) [=Malocystites emmonsi, *Sigmacystis emmonsi] K67
              |--Sinclairocystis Bassler 1950 K67
              |    |--*S. praedicta Bassler 1950 K67
              |    |--S. angulatus K67
              |    `--S. sulphurensis K67
              `--Amygdalocystites Billings 1854 [=Amygdalocystis Carpenter 1891; incl. Ottawacystites Wilson 1946] K67
                   |--*A. florealis Billings 1854 K67
                   |--A. laevis Billings 1883 [=A. florealis laevis, *Ottawacystites laevis] K67
                   |--A. radiatus K67
                   `--A. tenuistriatus K67

*Type species of generic name indicated

REFERENCES

[K67] Kesling, R. V. 1967. Paracrinoids. In Treatise on Invertebrate Paleontology pt. S. Echinodermata 1. General characters. Homalozoa-Crinozoa (except Crinoidea) (R. C. Moore, ed.) vol. 1 pp. S268-S288. The Geological Society of America, Inc., and The University of Kansas: Lawrence (Kansas).

[LS87] Lewis, R. D., J. Sprinkle, J. B. Bailey, J. Moffit & R. L. Parsley. 1987. Mandalacystis, a new rhipidocystid eocrinoid from the Whiterockian stage (Ordovician) in Oklahoma and Nevada. Journal of Paleontology 61 (6): 1222-1235.

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