The Echinoid Directory

Acrocidaris Agassiz, 1840, p. 27

[=Acrotiaris Quenstedt, 1872, p. 279.]

Diagnostic Features	Test flattened below and above; ambitus rounded. Apical disc small (less than one-quarter test diameter); rounded; plating dicyclic, the posterior oculars insert; Genital plates pentagonal, G2 distinctly larger. Periproct subangular, plating unknown. Large primary tubercle dominates each genital plate. Ambulacra straight, plating polygeminate throughout (5-6 pore-pairs to each primary tubercle; pore-pairs uniform and undifferentiated; more or less uniserial in arcs aborally, expanded adorally into phyllodes. Primary ambulacral tubercle to each plate; plate compounding with all elements reaching the perradius and overlapped by the primary tubercle at the ambitus. Interambulacral plates wider than tall; plates with a single large tubercle, centrally placed. Only a single narrow band of granules interradially. Ambulacral and interambulacral tubercles similar in size; perforate and crenulate (aboral tubercles with only traces of crenulation). Peristome about half test diameter; buccal notches very deep, giving the peristome a crenulated appearance. No sphaeridial pits. Spines long, subtrigonal in cross-section distally and with ribbed or keeled cortex. Lantern stirodont, with keeled teeth.
Distribution	Middle Jurassic (Bathonian) to Lower Cretaceous (Valanginian), western Europe.
Name gender	feminine
Type	Acrocidaris nobilis Agassiz, 1840, p. 52, by subsequent designation of Lambert & Thiery, 1914, p. 191. Syntype: Museum of Comparative Zoology Harvard University.
Species Included	A. nobilis Agassiz, 1840; Upper Oxfordian-Kimmeridgian, Europe. A. minor Agassiz, 1840; Valanginian, France. A. splendida (Cotteau, 1881); Oxfordian, Europe. A. striata (Agassiz, 1840); Bathonian, France.
Classification and/or Status	Acroechinoidea, Carinacea, Pseudodiadematidae.
Remarks	Distinguished by its small hemicyclic apical disc from all Emiratiidae. Pseudodiadema has much finer and more heterogeneous tuberculation and lacks the primary tubercles on its genital plates. Acropeltis is very similar but has trigeminate ambulacral plating. Agassiz, L. 1840. Description des Échinodermes fossiles de la Suisse. Partie 2, Cidarides. Memoires de la Societe des Sciences naturelle Helvetica 4, 107 pp., 11 pls. Lambert, J. & Thiery, P. 1909-1925. Essai de nomenclature raisonnee des echinides. Chaumont, Ferriere.