The Echinoid Directory

Isaster Desor, 1858, p. 359

[=Ismidaster Boehm, 1927, p. 194, type species Ismidaster toulai Boehm, 1927 ]

Diagnostic Features
  • Test ovate without anterior sulcus; tapering posteriorly. Test domed to weakly subconical in profile.
  • Apical disc central; ethmophract with three gonopores (no gonopore in genital plate 2).
  • Ambulacra all similar; all five ambulacra forming short, weakly sunken petals aborally.
  • Petals with smooth, narrow, undivided perradial zone.
  • Peristome D-shaped and facing downwards. Surrounded by a distinct rim.
  • Labral plate longitudinally elongate; only slightly shorter than sternal plates.
  • Periproct on short posterior truncate face; well below mid-height in posterior view; slightly inframarginal.
  • No fascioles.
  • Aboral tuberculation of small tubercles set in a groundmass of granules.
Late Cretaceous (Maastrichtian) to Early Tertiary (Palaeocene), Kazakhstan, Ukraine, Turkey, Spain.
Name gender masculine
Isaster aquitanicus, Desor, 1858 p. 359 (= Spatangus aquitanicus Grateloup, 1836, p. 74) by original designation.
Species Included
  • I. toulai (Boehm, 1927); Palaeocene, Turkey.
  • I. aquitanicus Desor, 1858; Maastrichtian and Palaeocene; Spain, Ukraine and Kazakstan.
Classification and/or Status

Spatangoida, Micrasterina, Micrasteridae, Cyclasterinae.

Presumed paraphyletic by exclusion of Isopatagus.


Differs from Isomicraster and Gibbaster in having a convex anterior margin without the trace of a frontal groove and in having no gonopore in genital plate 2. Differs from Cyclaster in having no fascioles and no frontal groove and by having pore-pairs in the frontal ambulacrum identical to those in the other ambulacra aborally. Differs from Isopatagus, which also has a petaloid anterior ambulacrum, in having shorter petals that do not extend to the ambitus.

Desor, E. 1855-1858. Synopsis des échinides fossiles. Reinwald , Paris, lxviii+490 pp., 44 pls.

A.B. Smith, J. Gallemi, C.H.Jeffery, G. Ernst & P.D. Ward 1999. Late Cretaceous-early Tertiary echinoids from northern Spain: implications for the Cretaceous-Tertiary extinction event. Bulletin of the Natural History Museum, London (Geology Series) 55, 81-137.

Stokes, R. B. 1986. The echinoid Isaster from the Danian of Turkey. Neues Jahrbuch fur Geologie und Palaontologie Mh 1986(3), 171-174.