Stratum.black
Micraster — Micraster
Micraster — FunkMonk, Wikimedia Commons, CC BY SA 3.0

Echinoid

Micraster

Chalk heart urchin

Micraster is the heart urchin of the English and French Upper Chalk, famous as the textbook example of evolutionary change through a rock sequence, and a common find on the Kent and Sussex cliffs and in flint form. Flint-filled Micraster ('shepherd's crowns') are cheap and folklore-rich. Chalk specimens are collected from fallen blocks on the foreshore.

PhylumEchinodermata
ClassEchinoidea
OrderSpatangoida
FamilyMicrasteridae
GroupEchinoid
Rank (PBDB)genus· Paleobiology Database
AuthorAgassiz 1836· Paleobiology Database
Classification (PBDB)Echinodermata › Echinoidea › Spatangoida › Micrasteridae· Paleobiology Database
Range (PBDB)100–56 Ma· Paleobiology Database
PBDB occurrences192· Paleobiology Database

Photographs

Micraster — Micraster (NHMUK PV P 14212 $1)
Micraster (NHMUK PV P 14212 $1) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0
Micraster — Micraster (NHMUK PV P 17273 (e) (1))
Micraster (NHMUK PV P 17273 (e) (1)) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0
Micraster — Micraster (NHMUK PV OR 43512 a $1)
Micraster (NHMUK PV OR 43512 a $1) — © The Trustees of the Natural History Museum, London, Natural History Museum (London) Data Portal, CC BY 4.0

Age

Elsewhere

Cite this article

Stratum Study. "Micraster" (Taxon). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/taxa/micraster. Accessed 2026-09-20.

BibTeX · CSL-JSON

@misc{stratum-micraster,
  title        = {Micraster},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/taxa/micraster}},
  year         = {2026},
  note         = {Taxon article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, pbdb, wikidata, commons, nhm. Accessed 2026-09-20.}
}

Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.