The Echinoid Directory

Araeosoma Mortensen, 1903, p. 53

Diagnostic Features
  • Apical disc monocyclic, with ocular and genital plates forming an unbroken circle. Gonopores open in membranous region outside genital plates, which may be composite.
  • Ambulacra trigeminate, with a single large element reaching the perradial suture and two small demiplates positioned centrally and abutting one another. Only becoming adradial in position close to the apex and peristome.
  • Pore-pairs arranged in three series.
  • Ambulacral zones about two-thirds the width of interambulacral zones at the ambitus.
  • Interambulacral plates with prominent membranous gaps along horizontal sutures.
  • Aborally a single primary interambulacral tubercle on every second or third plate only; rest of plate with just sparse granulation. Adorally each interambulacral plate with a prominent adradial tubercle in the type species.
  • Shallow buccal notches.
  • Only ambulacral plates extending over the peristome, with pore-pairs arranged biserially in each zone.
  • Oral spines ending in expanded cone-shaped hyaline hoof.
  • Sphaeridium present only on the inner of the two demi-plates in each triad.
  • Dactylous pedicellariae present.
Pliocene, New Zealand; Recent, Indo-Pacific and Atlantic.
Name gender neuter
Calveria fenestratum Thomson, 1872, p. 494, by original designation.
Species Included
  • A. fenestratum (Thomson, 1872); Recent, NE Atlantic.
  • A. violaceum Mortensen, 1903; Recent, NE Atlantic.
  • A. belli Mortensen, 1903; Recent, West Indies.
  • A. parviungulatum Mortensen, 1934; Recent, Celebes.
  • A. eurypatum Agassiz & Clark, 1909; Recent, Hawaii.
  • A. leptaleum Agassiz & Clark, 1909; Recent, East Pacific.
  • A. splendens Mortensen, 1934; Recent, Kei Islands.
  • A. owstoni Mortensen, 1904; Recent, West Pacific.
  • A. coriaceum (Agasssiz, 1879); Recent, Indo-Pacific.
  • A. tesselatum (Agassiz, 1879); Recent, Malay Archipelago, China Sea.
  • A. paucispinum Clark, 1924; Recent, South Africa.
  • A. thetidis (H. L. Clark, 1909); Recent, Australia, New Zealand.
Classification and/or Status

Euechinoidea; Echinothurioida; Echinothuriidae; Echinothuriinae.



Distinguished from Calveriosoma by having dactylous pedicellariae and obvious membranous gaps between interambulacral plates on the adapical surface. Differs from Hapalosoma by having admedial and ambulacral primary tubercles, although this may partially reflect the considerable size difference between the two type species. Mortensen (1935) separated Araeosoma from these two genera solely on the characteristics of their dactylous pedicellariae (absent in Calveriosoma, present in Araeosoma and Hapalosoma, the latter having the valves reduced to just their basal parts). However, Mortensen, himself (1935: 221) indicated that the three genera might better be considered as subgenera. In the absence of pedicellariae tests may be difficult to differentiate.

Differs from Asthenosoma in having large membranous gaps at the outer end of genital plates through which the gonopores open, and with sparser and smaller primary tubercles on the oral surface.

A cladistic analysis of extant species has been carried out by Mooi et al. (2004).

Mooi, R., Constable, H., Lockhart, S. & Pearse, J. 2004. Echinothurioid phylogeny and the phylogenetic significance of Kamptosoma (Echinoidea: Echinodermata). Deep Sea Research II 51, 1903-1919.

Mortensen, T. 1903. The Danish Ingolf-Expedition 1895-1896. Vol. 4, No. 2. Echinoidea, pt. 1, 198 pp., 21 pls. Bianco Luno, Copenhagen.

Mortensen, T. 1935. A monograph of the Echinoidea. Volume 2, Bothriocidaroida, Melonechinoida, Lepidocentroida and Stirodonta. C.A. Reitzel, Copenhagen.