The Echinoid Directory

Bromidechinus Smith & Savill, 2001, p. 138

Diagnostic Features
  • Test small, composed of relatively thin, imbricate plates; shape unknown.
  • Periproct a mass of small plates.
  • Five ambulacral and five interambulacral zones. Ambulacral zones composed of a single perradial column of hexagonal plates bounded on either side by subrectangular plates that are perforated by a single slit-like opening.
  • Radial water vessel presumed internal; small perradial flanges to the perforate plate but these do not meet to fully enclose the water vessel.
  • Perforate plates with a small non-mamelonate granule on either side of the perforation.
  • Interambulacral zones uniserial towards apex, biserial at ambitus; with small, scattered granules covering plates but no tubercles.
  • Peristome small; plating unknown.
  • Lantern structure unknown.
  • Spines small straight and simple, confined to ambulacral plates.
Burrellian, Early Caradoc, Middle Ordovician of Oklahoma, USA.
Name gender masculine
Type Bromidechinus rimaporus Smith & Savill, 2001, p. 141 by original designation.
Species Included
  • Only the type species.
Classification and/or Status

Stem group Echinoidea; unnamed plesion.



The plating structure in Bromidechinus is similar to that seen in ophiocistioids and Smith & Savill (2001) place this as the most primitive known echinoid.

Smith, A.B. & Savill, J. J. 2001. Bromidechinus, a new Middle Ordovician Echinozoa (Echinodermata), and its bearing on the early history of echinoids. Transactions of the Royal Society of Edinburgh 91, 137-147.