The Echinoid Directory

Contributed by Andrew Smith, October 2006

Heterodiadema Cotteau, 1864, p. 521

Diagnostic Features
  • Test circular, depressed in profile with ambitus about mid-height.
  • Apical disc large, key-hole shaped and projecting into the posterior interambulacrum, this projection getting deeper in larger individuals. Plating not preserved, presumed monocyclic; interradial notches distinct.
  •  Ambulacra straight and moderately broad, with trigeminate ambulacral plating; all elements reaching the perradial suture, but with central element the largest. Pore-pairs uniserially arranged throughout. A large primary tubercle overlaps all three elements of a compound plate on ambital and adoral plates. Above the ambitus tubercles decrease in size markedly and take up an adradial poisiton, but still straddle all three elements; A broad granular zone is present perradially above the ambitus.
  • Interambulacral plates wider than tall, each with a large subcentral primary tubercle, with a slightly incised areole. Primary tubercles decrease in size markedly on the upper surface. Well developed adradial and interradial zones of granulation are developed, especially aborally.
  • Tubercles perforate and crenulate up to the ambitus; smaller primary tubercles on apical surface usually imperforate and non-crenulate.
  • Peristome slightly sunken, with deep buccal notches that have a small tooth-like partition. Long, naked and slightly sunken zones extend along the adradial margin of interambulacral zones behind each buccal notch.
  • Spines and lantern unknown.
Distribution Upper Cretaceous (Cenomanian) of southern Europe; North Africa (including Niger) and the Middle East as far as Karakorum.
Name gender neuter
Type Hemicidaris libyca Desor, in Agassiz & Desor, 1846, p. 338, by monotypy.
Species Included
  • H. libycum Desor, in Agassiz & Desor, 1846; Cenomanian, North Africa, Middle East
  • H. ourmemense de Loriol, 1890; Cenomanian, Portugal.
Classification and/or Status Euechinoidea, Acroechinoidea, Diadematoida, Heterodiadematidae
Remarks Although no lantern has yet been described from this taxon, it seems likely that Heterodiadema is a diadematoid, based on its tuberculation and deep buccal notches.  It is very close to Trochodiadema in test morphology, but that genus has a regular apical disc that is not extended posteriorly.  Juvenile Heterodiadema and Trochodiadema may be very difficult to differentiate. 

Cotteau, G. H. 1862-1867. Paléontologie Française. Terrain Crétace, Tome Septième. Échinides. Masson et fils, Paris. 892 pp., pls 1007-1204.

Geys (1980) reported the presence of Heterodiadema lybica from the Campanian of Belgium, but this was based on an old museum collections and likely represents a mislabelled specimen.

Geys, J. F. 1980. Heterodiadema libycum (Agassiz & Desor, 1846) . a hemicidaroid echinoid from the Campanian of Belgium.  Anales de la Societe geologique du Nord 99, 449-451.

Smith, A. B., Simmons, M. D. & Racey, A. 1990. Cenomanian echinoids, larger foraminifera and calcareous algae from the Natih Formation, central Oman Mountains. Cretaceous Research 11, 29-69.