The Echinoid Directory

Echinothrix Peters, 1853, p. 484

[= Garelia Gray, 1855, p. 36, type species Garelia aequalis Gray 1855 (=Echinus calamaris Pallas, 1774) (objective); = Savignya Desor, 1855, p. 82 (subjective) ]

Diagnostic Features
  • Test plating rather fragile; plating effectively rigid throughout although adapical plates have slightly imbricate sutures.
  • Apical disc monocyclic with large circular periproct lacking larger periproctal plates; genital plates strongly projecting interradially.
  • Ambulacra straight; pore-pairs non-conjugate, in very weakly offset triads.
  • Ambulacral plating trigeminate with large adradial primary tubercle and four or more slightly smaller tuberlces perradially.
  • Interambulacral zone wide, with ambital plates distinctly wider than tall.
  • Naked interradial zone adapically (in type species only).
  • Two subequal primary tubercles on ambital plates, sometimes more in larger species; all tubercles perforate and crenulate.
  • Peristome much larger than apical disc, with deep, rounded buccal notches associated with adradial tags.
  • Spines: ambulacral spines long and slender; hollow, with longitudinal ridges and non-verticillate ornament. Interambulacral spines long and slender but distinctly wider than ambulacral spines; hollow with loose stereom, distinctly verticillate in the type species.
Recent; Indo-Pacific.
Name gender feminine
Echinus calamaris Pallas, 1774, by subsequent designation of Mortensen, 1940, p. 283.
Species Included
Classification and/or Status

Diadematoida; Diadematidae.

Presumed monophyletic.


Differs from Diadema in ambulacral tuberculation. In Diadema there is only a single primary ambulacral tubercle to each compound plate whereas in Echinothrix the primary tubercle is joined by four to six other tubercles only a little smaller, and the perradial tuberculate band thus appears broad and densely tuberculate.

Echinothrix diadema can be distinguished from the type species by: ambulacra not raised aborally, no naked median area in the interambulacra; periproct not largely swollen, with no white platelets present in the membrane.

Ambulacral spines of E. diadema similar to the type species, however, interambulacral spines are distinct in that they are non- verticillate, having longitudinal ridges, with spines distinctly flaring distally in adults.

This genus has been reviewed by Coppard & Campbell (2006a, b).

Coppard, S. E. & Campbell, A. C. 2006a. Taxonomic significance of test morphology in the echinoid genera Diadema Gray, 1825 and Echinothrix Peters, 1853 (Echinodermata). Zoosystema 28, 93-112.

Coppard, S. E. & Campbell, A. C. 2006b. Systematic significance of trident pedicellariae in the echinoid genera Diadema and Echinothrix. Invertebrate Biology 125, 363-378.

Mortensen, T. 1940. A monograph of the Echinoidea. Volume III. 1, Aulodonta. C.A. Reitzel, Copenhagen.

Peters, W. 1853. Monatsber. Akad. Berlin 1853, p. 487.