Achistrum

Achistrum sp., copyright Richard Paselk.

Belongs within: Apodida.

Achistrum was first described as a genus of hook sclerites known from the Devonian to the Cretaceous of Europe and North America (Boczarowski 2001; Frizzell & Exline 1966).

Characters (from Frizzell & Exline 1966): Eye at 90 degrees to plane of spear, rim entire; eye open or crossed by simple or bifurcating crossbars.

<==Achistrum Etheridge 1881 B01 (see below for synonymy)
    |--*A. nicholsoni Etheridge 1881 B01
    |--A. bartensteini FE66
    |--A. bathonianum FE66
    |--A. bichordatum FE66
    |--A. breve FE66
    |--A. brownwoodense FE66
    |--A. frizzelli FE66
    |--A. gamma FE66
    |--A. huckei FE66
    |--A. issleri FE66
    |--A. ludwigi FE66
    |--A. monochordatum FE66
    |--A. multiperforatum Beckmann 1965 [=A. (Porachistrum) multiperforatum] B01
    |--A. permianum FE66
    |--A. trichordatum FE66
    |--A. tuto Boczarowski 2001 B01
    `--A. varicum Boczarowski 2001 B01

Achistrum Etheridge 1881 B01 [incl. Achistrulum Deflandre-Rigaud 1961 FE66, Ancistrum Bather 1900 non Maupas 1883 FE66, Cancellrum Hampton 1958 FE66, Spinrum Hampton 1958 FE66]

*Type species of generic name indicated

REFERENCES

[B01] Boczarowski, A. 2001. Isolated sclerites of Devonian non-pelmatozoan echinoderms. Palaeontologia Polonica 59: 1–219.

[FE66] Frizzell, D. L., & H. Exline. 1966. Holothuroidea—fossil record. In: Moore, R. C. (ed.) Treatise on invertebrate Paleontology pt U. Echinodermata 3 vol. 2 pp. U646–U672. The Geological Society of America, Inc., and The University of Kansas Press.