The Echinoid Directory

Contributed by Andrew Smith, March 2012

Australidiadema Smith & Crame, 2012, p. 313

Diagnostic Features	Apical disc unknown Ambulacra narrow, plating trigeminate with pore-pairs in offset triads on oral surface. All elements reaching the perradius and similar in size. Primary tubercle overlaps two of the three elements and present on each triad; a much smaller secondary tubercle alternates with the primary and is positioned more perradially. Interambulacral zones wide. On oral surface close to peristome with primary tubercle flanked by smaller tubercles on either side. At ambitus and above single primary tubercle dominates each plate. Adapical plates may lack primary tubercles All tubercles perforate and strongly crenulate. Lantern with grooved teeth Spines with hollow lumen and shaft ornamented with fine spinelets irregularly distributed.
Distribution	Lower Cretaceous (Aptian), Alexander Island, Antarctica
Name gender	neuter
Type	Australidiadema alexanderi Smith & Crame, 2012, p. 313 (holotype BAS KG.1681.14)
Species Included	Only the type species
Classification and/or Status	Diadematoida, Diadematidae
Remarks	The combination of nonverticillate spine morphology with strongly differentiated primary tubercles that become more prominent towards the ambitus and the ambulacral plating with primary and secondary tubercles alternating gives this taxon a unique appearance. Smith, A. B. & Crame, J. A. 2012. Echinoderm faunas from the Lower Cretaceous (Aptian-Albian) of Alexander Island, Antarctica. Palaeontology 55, 305-324.