These irregular sea urchins are characterized by a particularly marked bilateral symmetry, including for the apical system, which is highly elongated. In some contemporary abyssal groups such as Pourtalesiidae, some species are even bottle-shaped. The mouth (peristome) does not contain an Aristotle's lantern. The anus (periproct) has migrated towards the periphery of the test. The plastron is never amphisternous.^[1]

•  
  Fossile of Hemipneustes pyrenaicus (Hemipneustidae, Maastrichtian)
•  
  Echinosigra amphora (Pourtalesiidae)

This order seems to have appeared at the lower Cretaceous.^[1]

According to World Register of Marine Species :

• † Family Disasteridae Gras, 1848
  • genus † Disaster L. Agassiz, 1835
• Family Hemipneustidae (Lambert, 1917) †
  • genus Hemipneustes L. Agassiz, 1835 †
  • genus Medjesia Jeffery, 1997 †
  • genus Opisopneustes Gauthier, 1889 †
  • genus Plesiohemipneustes Smith & Wright, 2003 †
  • genus Toxopatagus Pomel, 1883 †
• Suborder Meridosternata (Lovén, 1883)
  • Infraorder Cardiasterina †
    • Family Cardiasteridae Lambert, 1917 †
    • Family Stegasteridae Lambert, 1917f †
  • Family Echinocorythidae Wright, 1857 †
  • Family Holasteridae Pictet, 1857 †
    • Genus Salvaster Saucède, Dudicourt & Courville, 2012 †
  • Infraorder Urechinina
    • Family Calymnidae Mortensen, 1907
    • Family Carnarechinidae Mironov, 1993
    • Family Corystusidae Foster & Philip, 1978
    • Family Plexechinidae Mooi & David, 1996
    • Family Pourtalesiidae A. Agassiz, 1881
    • Family Urechinidae Duncan, 1889
• Family Pseudholasteridae (Smith & Jeffery, 2000) †
  • genus Eoholaster Solovjev, 1989 †
  • genus Giraliaster Foster & Philip, 1978 †
  • genus Pseudholaster Pomel, 1883 †
  • genus Taphraster Pomel, 1883 †
• Family Stenonasteridae (Lambert, 1922) †
  • genus Stenonaster Lambert, 1922 †

• Holasteroida at the Natural History Museum
• Kroh A, Mooi R (eds.). "Holasteroida". World Echinoidea Database. World Register of Marine Species.