The Echinoid Directory

• Test plating rather fragile, although plating effectively sutured throughout.
• Apical disc hemicyclic with ocular plates II and III exsert in the type species. Large circular periproct without enlarged periproctal plates; genital plates projecting strongly interradially.
• Ambulacra narrow and straight; pore-pairs non-conjugate, uniserial; phyllodes developed adorally.
• Ambulacral plating trigeminate with single large primary tubercle per plate except adorally where there may be fewer.
• Interambulacral zone wide, with ambital plates distinctly wider than tall.
• 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 very long and slender; hollow and with verticillate ornament.

Recent, Indo-Pacific and Atlantic.

Echinometra setosa Leske, 1778, by ruling of the ICZN, 1954.

• D. setosum (Leske, 1778); Recent, Indo-Pacific.
• D. antillarum Philippi, 1845; Recent, Caribbean and Atlantic (D. ascensionis Mortensen, 1909 (Recent, Central Atlantic) is a subspecies).
• D. paucispinum A. Agassiz, 1863; Recent, Hawaii.
• D. mexicanum A. Agassiz, 1863; Recent, west coast of America.
• D. savignyi Michelin, 1845; Recent, Indo-West Pacific.
• D. palmeri Baker, 1967; Recent, New Zealand, south eastern Australia.

Diadematoida; Diadematidae.

Monophyletic.

Differs from Echinothrix 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.

In the past hollow verticillate diadematoid spines in the fossil record have been assigned to the genus Diadema. However, these are basically indeterminate. Diadema palmeri is distinct within the genus in having a monocylclic apical disc.  The species were reviewed by Coppard & Campbell (2006a, b).

Baker, A.N. 1967. Two new echinoids from northern New Zealand, including a new species of Diadema. Transactions of the Royal Society of New Zealand 8(23), 239-245, pls 1-3.

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.

Gray, J. E. 1825. An Attempt to divide the Echinida, or Sea Eggs, into Natural Families. Annals of Philosophy, new series 10, 423-431.

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