• Edrioasteroidea
• stemmed crinoids and their descendants
  • paraphyletic assemblage of "eocrinoids"
  • Blastozoa
    • Rhombifera
    • Diploporita
    • Blastoidea
  • armed echinoderms and their descendants
    • Crinoidea
    • Eleutherozoa
      • Asterozoa
        • Ophiuroidea
        • Asteroidea
      • Echinozoa
        • Echinoidea
        • Holothuroidea

Echinoderms first appear in Early Cambrian, and remain very diverse.

Homolazoa

• Odd, asymmetrical early Paleozoic echinoderms
• Middle Cambrian to Late Ordovician
• Motile suspension feeders
• Some have interpreted these as ancestral to the vertebrates (making vertebrates a clade within Echinodermata), though most dispute this suggestion

Helicoplacoidea

• Early Cambrian only
• Body is helically-built (hence name)
• Sessile suspension feeders: ambulacral groove spiralling along body

Edrioasteroid

• Early Cambrian to end of Pennsylvanian
• Sessile, benthic, attached to surfaces of brachiopods, mollusks, etc.
• Have five ambulacra, like more derived forms

"Eocrinoids"

• Paraphyletic group of basal stalked echinoderms
• Early Cambrian through Silurian
• Ones with brachioles may actually be basal blastozoans
• Others, with simple arms, may be sister taxa to Crinozoa + Eleutherozoa

Blastozoa

• Ambulacra are lined with brachioles (tiny tentacles surrounded by calcitic rings, only rarely preserved
• Tend to have relatively complex breathing structures
• Tend to have relatively large calyces (or thecae)
• Three major clades of blastozoans (the first two traditionally lumped into "Cystoidea"):
  • Rhombifera: Early Ordovician to Late Devonian, respired through pore rhombs (slits in theca)
  • Diploporita: Early Ordovician to Late Devonian, respired through diplopores (paired holes)
  • Blastoidea: Possibly Ordovician, DEFINITELY Silurian to end of Permian, respired through ambulacral holes over hydrospires (complex foldings in body of theca)

Crinoidea (sea lilies and feather stars)

• Ancestrally stalked forms, but various taxa (such as modern Comatulida) are free-living
• Ordovician onward (although major extinction at Permo-Triassic boundary)
• Peak in Mississippian (with blastoids)
• Suspension feeders: long arms arrayed into current

Ophiuroidea (brittle stars)

• Early Ordovician onward, but relatively rare as fossils
• Arms lack ambulacral grooves, but have central disk
• Fastest moving echinoderms
• Like holothurians, are VERY abundant in deep water
• Suspension feeders

Asteroidea (starfish or sea stars)

• Early Ordovician onward, but relatively rare as body fossils (good trace fossil record)
• No central disk, but have ambulacral grooves in the arms
• Use tube legs primarily as organs of locomotion rather than passing food to the mouth
• Carnivores, primarily bivalve eaters (evert stomach to digest on the outside of their body!)

Echinoidea (sea urchins)

• Very diverse, best eleutherozoan fossil record due to integration of test
• Late Ordovician onward
• Grazers/scavengers, feeding by means of complex Aristotle's Lantern (mouth parts)
• Often spinose
• In Jurassic onward, evolution of infaunal irregular echinoids, with new antero-posterior symmetry, including:
  • "Sea biscuts": paraphyletic grade of sediment-feeding spatangoids and cassiduloids
  • "Sand dollars": monophyletic clade (Clypeasteroidea), suspension feeders

Holothuroidea (sea cucumbers)

• Early Cambrian (based on isolated sclerites) onward, but very spotty fossil recod
• No rigid test, only calcareous sclerites suspended in fleshy tissue
• Motile, mostly infaunal: major bioturbators
• Sediment and suspension feeders
• Range from very shallow water to deep sea

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