Achistrum

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 1881B01 (see below for synonymy)
    |--*A. nicholsoni Etheridge 1881B01
    |--A. bartensteiniFE66
    |--A. bathonianumFE66
    |--A. bichordatumFE66
    |--A. breveFE66
    |--A. brownwoodenseFE66
    |--A. frizzelliFE66
    |--A. gammaFE66
    |--A. huckeiFE66
    |--A. issleriFE66
    |--A. ludwigiFE66
    |--A. monochordata Hodson et al. 1956SG93
    |--A. multiperforatum Beckmann 1965 [=A. (Porachistrum) multiperforatum]B01
    |--A. permianumFE66
    |--A. trichordatumFE66
    |--A. tuto Boczarowski 2001B01
    `--A. varicum Boczarowski 2001B01

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.

[SG93] Simms, M. J., A. S. Gale, P. Gilliland, E. P. F. Rose & G. D. Sevastopulo. 1993. Echinodermata. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 491–528. Chapman & Hall: London.