Diagnostic Features：
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.
Distribution：Recent, Indo-Pacific and Atlantic.
Type：Echinometra setosa Leske, 1778, by ruling of the ICZN, 1954.
Species Included：
· 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, southeastern Australia.
Classification and/or Status： Euechinoidea; Diadematoida; Diadematidae.
Monophyletic.
Remarks：
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.
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.
Mortensen, T. 1940. A monograph of the Echinoidea. Volume III. 1, Aulodonta. C.A. Reitzel, Copenhagen.
· Key to species
Mollusca 軟體動物門 (6)
