Flexibilia

From Palaeos

o Echinodermata
`--+--Echmatocrinus brachiatus
   `--o Crinoidea
      |--Aethocrinida
      `--+--Disparida
         `--+--Camerata
            `--Cladida (incl. Flexibilia and Articulata)

Description

Time: Middle Ordovician – Upper Permian.

Description: (from Moore, 1978) Cup and tegmen flexible, the latter with exposed mouth and food grooves. Crown ovoid to globose, with closely abutting, invariably uniserial arms incurved distally. Arms distinctly differentiated from cup or with proximal brachials and interarm plates merging uniterruptably with radials and two subjacent plate circlets, nearly all joined by ligaments rather than by solid union. Three infrabasals with small one in C ray and large ones in AB and DE rays, or rarely fused into single disc or resorbed. Five basals and five radials subequal in each circlet. Radianal commonly present, either directly below C radial or shifted obliquely left. Anal X plate inserted between posterior radials. Arms nonpinnulate, generally branching isotomously or both heterotomously and isotomously, very rarely atomous. Supplementary plates may be developed interradially as well as interbrachially. Flexible tegmen lacking anal sac but containing five distinct orals in many genera (posterior one largest), rows of ambulacrals leading from arm bases to exposed mouth, and large areas of small interambulacral plates. Stem round in transverse section or very rarely crescentic, composed of thin columnals; no cirri.

Phylogeny

<==Flexibilia [Anisocrininae, Articulosa]
   |--Taxocrinites
   |    |  i. s.: Onychocrinus [Onychocrinidae]
   |    |--Taxocrinida
   |    `--Sagenocrinida
   |         |  i. s.: Sagenocrinus [Sagenocrinidae]
   |         |--Ichthyocrinidae
   |         `--Sagenocrinitacea
   |--Calpiocrinites
   |    |--Pentamerocrinus Jaekel 1918 [Pentamerocrinidae]
   |    |    `--*P. praematurus Jaekel 1918
   |    `--Homalocrinidae [Calpiocrinidae]
   |         |--Asaphocrinus Springer 1920
   |         |--Homalocrinus
   |         |--Calpiocrinus Angelin 1878
   |         `--Wachsmuthicrinus
   `--Lecanocrinites
        |--Lecanocrinidae
        |    |--Lecanocrinus Hall 1852 [incl. Alsopocrinus Tansey 1924]
        |    `--Pycnosaccus
        |--Edriocrinidae
        |    |--Edriocrinus
        |    `--Lodanella
        |--Nipterocrinidae
        |    |--Nipterocrinus
        |    |--Calycocrinus
        |    `--Palaeoholopus
        `--Mespilocrinidae
             |--Mespilocrinus
             |--Syntomocrinus
             `--Geroldicrinus Jaekel 1918
                  `--*G. roemeri [=Lecanocrinus roemeri]

* Type species of genus indicated

References

Eckert, J. D., & C. E. Brett. 2001. Early Silurian (Llandovery) crinoids from the Lower Clinton Group, western New York State. Bulletins of American Paleontology 360: 1-88.

Fenton, C. L., & Fenton, M. A. 1958. The Fossil Book. Doubleday & Co.: New York.

Jaekel, O. 1918. Phylogenie und System der Pelmatozoen. Paläontologische Zeitschrift 3: 1-128.

Moore, R. C., C. G. Lalicker & A. G. Fischer. 1952. Invertebrate Fossils. McGraw-Hill Book Company, Inc.: New York.

Credits

CKT061123 (Phylogeny); CKT071120 (Description)