The Echinoid Directory

Mesodiadema Neumayr, 1889, p. 372

[= Loriolella Fucini, 1904, p. 1, type species Cidarites ludovicii Meneghini, 1867, p. 17 (=Hemipedina marconissae Desor, 1856, p. 59); = Pseudopygaster Hawkins, 1922, p. 316, type species Pseudopygaster eos Hawkins, 1922 ]

Diagnostic Features
  • Test small, subglobose, with rounded ambitus.
  • Apical disc etremely large, more than 50% test diameter. Plating lost.
  • Ambulacra narrow and straight. Plating simple throughout. Pore-pairs small spaced and subhorizontal aborally, more crowded and single pored adorally. Uniserially arranged from apex to peristome.
  • Aboral ambulacral plates with small primary tubercle, every third slightly larger. Adoral plates with more numerous and subequal granules in rows.
  • Interambulacra wide; plates about twice as wide as tall at ambitus. Each with a large primary tubercle with a perforate mamelon and non-crenulate platform and surrounded by aslightly incised areole. Areolar circles not confluent. No differentaited scrobicular tubercles, but dense uniform small secondaries cover the remainder of the plate.
  • Peristome very small, slightly sunken, circular with faint buccal notches.
  • Perignathic girdle of short auricles that do not converge perradially.
Distribution
Early Jurassic, Pliensbachian, Italy.
Name gender neuter
Type
Hemipedina marconissae Desor, 1856, p. 59, by original designation.
Species Included
  • Only the type species.
Classification and/or Status

Euechinoidea; stem group Irregularia.

Monotypic.

Remarks

Identical to small individuals of Loriolella.

Neumayr, M. 1889. Der Stamme der Thierreiches. Wirbellose Thiere. Wien & Prague, 604 pp.

Smith, A. B. & Anzalone, L. 2000. Loriolella, a key taxon for understanding the early evolution of irregular echinoids. Palaeontology 43, 303-324.