The Echinoid Directory

• Test low and rather thin-plated.
• Apical disc and peristome about 50% test diameter. Apical disc dicyclic; plates generally covered in tubercles. Ocular pores rimmed. Sexual dimorphism in gonopore size; gonopores large and marginal in females, in part bounded by interambulacral plates.
• Interambulacra of relatively few plates (up to 10). Tubercles perforate and non-crenulate with sunken areoles. Scrobicular circle not differentiated from other secondary tubercles; outside areole plate uniformly covered in secondary tubercles with no naked interradial zone.
• Ambulacra almost straight. Pore-pairs very small and oblique, usually with the two pores coalesced by loss of the interporal partition. Primary and smaller secondary tubercle to each ambulacral plate. Pore zones not sunken.
• No naked perradial zone or pits developed.
• Peristome with well developed series of ambulacral plates.
• Primary spines long, cylindrical, with short collar and distinct neck. Shaft ornamented with irregular thorns, with fine dense hairs in between. In some species primary spines become spatulate distally.
• Secondary spines slightly swollen distally.

Recent, Antarctica; possibly Danian, western Europe.

Ctenocidaris speciosa Mortensen, 1910, p. 4, by original designation.

Cidaroida; Ctenocidaridae.

?

According to Mortensen (1928) the only character that distinguishes Eurocidaris from Ctenocidaris is that its oral primary spines are simple and undifferentiated; those of Ctenocidaris being decidedly serrate and spear-shaped. Aporocidaris has a significantly larger apical disc and Rhynchocidaris has a characteristic triple pore structure adorally and clavate secondary spines. However, the differences between these taxa is pretty minimal and probably does not merit separation at genus level.

Smith & Jeffery (2000) tentatively assign certain interambulacral plates from the Palaeocene to this genus on the basis of their tuberculation.

Mortensen, T. 1928. A monograph of the Echinoidea. 1, Cidaroidea. C. A. Reitzel, Copenhagen.

McKnight, D. G. 1974. Some echinoids new to New Zealand. NZOI Records 2, 25-44.

Smith, A. B. & Jeffery, C. H. 2000. Maastrichtian and Palaeocene echinoids: a key to world faunas. Special Papers in Palaeontology 63, 1-406.