The Echinoid Directory

• Test elliptical in outline, with long axis passing through ocular plate IV and genital plate 1.
• Apical disc hemicyclic with posterior ocular plates insert in adults.
• Ambulacra polygeminate, with anywhere from 9 to 11 pore-pairs to a plate. In the type species pore-pairs are arranged in a double arc round the margin of the plate. In other species pore-pairs may be more irregular or form a broad irregular band.
• All ambulacral plates with single large primary tubercle occupying most of the plate surface.
• Interambulacral plates with large primary tubercle with massive mamelon and thick boss flanked by almost equally as large secondary tubercles on ambital plates.
• Peristome elliptical with feeble buccal notches.
• Ambulacra expand to form wide phyllodes adorally.
• Spines stout, facetted; about half test diameter in length. Secondary spines clavate.

Miocene, Australia; Recent, Tonga Islands.

 Zenocentrotus kellersi A.H. Clark, 1931, by original designation.

• Z. kellersi Clark, 1931; Recent, Tonga Islands.
• Z. paradoxus Clark, 1931; Recent, Tonga Islands.
• Z. peregrinus Philip 1965; Miocene, Australia.

Camarodonta; Echinoida; Echinometridae.

Presumed monophyletic.

Differs from Heterocentrotus Brandt, 1835, in possessing finer spines and a distinct marginal frill of longer subambital spines. Its secondary spines are not reduced to peg-like structures. Also may differ from Heterocentrotus and Podophora in orientation of the major axis of its test. In Zenocentrotus, according to Clark, the major axis passes through Amb. IV - Iamb. 1, whereas in Heterocentrotus and Podophora the major axis is through Amb. II - Iamb. 4. However, the orientation of the major axis in these taxa can be difficult to measure precisely, and there may be some intraspecific variation. In other respects the test architecture appears identical. Forms a clade with Heterocentrotus, Podophora and Colobocentrotus.

Clark, A. H. 1931. Echinoderms from the Islands of Niuafoou and Nukualofa, Tonga Archipelago. Proceedings of the U.S. National Museum 80(5), 1-12, pls 1-8.

G. Philip (1965 The Tertiary echinoids of south-eastern Australia III Stirodonta, Aulodonta, and Camarodonta (1). Proceedings of the Royal Society of Victoria 78, 181-196) described a possible fossil recpresentative of this genus based on spines and test fragments.