The Echinoid Directory

Acrocladia Agassiz, 1840, p. 19

Diagnostic Features
  • Test elliptical in outline, with long axis passing through ocular plate II and genital plate 4.
  • Apical disc dicyclic; periproct relatively small.
  • Ambulacra polygeminate, with anywhere from 14 to 19 pore-pairs to a compound plate. Pore-pairs tending to form a double arc in places.
  • All ambulacral plates with single large primary tubercle occupying most of the plate surface.
  • Interambulacral plates with single large primary tubercle with massive mamelon and thick boss at ambitus. There are flanking secondary tubercles on the adoral surface.
  • Peristome elliptical with feeble buccal notches.
  • Wide phyllodes developed adorally.
  • Spines very thick and dense; with three or more flattened facets. Never modified to scales or plates.
  • Secondary spines truncate and stubby.
Recent; Indo-West Pacific.
Name gender feminine
Echinus trigonarius Lamarck, 1816 by subsequent designation of Pomel, 1883, p. 77.
Species Included
  • Only the type species.
Classification and/or Status

Camarodonta; Echinoida, Echinometridae.

Subjective junior synonym of Heterocentrotus Brandt, 1835.


Very similar to Heterocentrotus mammillatus (Linnaeus, 1756) but in that species the ambulacral tubercles are sharply reduced in size above the ambitus, the adoral ambulacral zone is less petalloid, and there are fewer ambulacral pore-pairs to a plate (generally 9-12 as opposed to 15-16 in H. trigonarius).

Agassiz, L. 1840. Catalogus systematicus Ectyporum Echinodermatum fossilium Musei Neocomiensis, secundum ordinem zoologicum dispositus; adjectis synonymis recentioribus, nec non stratis et locis in quibus reperiuntur. Sequuntur characteres diagnostici generum novorum vel minus cognitorum, 20 pp. Oliv. Petitpierre, Neuchâtel.

Mortensen, T. 1943. A monograph of the Echinoidea III.3. Camarodonta 2. Echinidae, Strongylocentrotidae, Parasaleniidae, Echionometridae. C. A. Retzel, Copenhagen.