Dendrocrinidae

Classification
Phylum: Echinodermata
Class: Crinoidea
Order: Cladida
Family: Dendrocrinidae (Wachsmuth & Springer, 1886)
Cincinnatian Genera: Plicodendrocrinus

Geologic Range
Middle Ordovician – Late Devonian

Common Paleoecology
Dendrocrinidae is an extinct family of stationary intermediate-level epifaunal suspension feeders

Description of the Family

  • Cup steeply conical
  • Infrabasals strongly upflared, visible from side
  • Radial arm facets narrow, horseshoe-shaped, smooth or with fine radial culmina
  • Arms rounded, slender, branching repeatedly

Published Descriptions

Treatise on Invertebrate Paleontology, Part T, Vol. 2(2) (1978):

  • Cup steeply conical; infrabasals strongly upflared, visible from side; radianal directly below or obliquely left below C radial, anal X in line with radials and above CD basal. Radial arm facets narrow, horseshoe-shaped, smooth or with fine radial culmina. Arms rounded, slender, branching repeatedly, with strong tendency toward heterotomy.
  • Chief primitive features of the Dendrocrinidae are the steeply conical form of the cup, structure of its posterior side, and the smooth, outwardly directed radial facets. The rounded facets are horseshoe shaped and narrow. The arms are strongly rounded and branch isotomously several times, representing an advanced evolution of nonpinnulate ray structure. An archaic feature of Dendrocrinus is the occurrence of a radianal directly below the C radial. The very tall anal sac, formed of a number of vertical rows of thin plicate plates, is a distinctive attribute of the family that is very unlike the sacs of merocrinids and cupulocrinids but closely similar to those of botryocrinid genera and others, which are inferred to belong in the same genetic line as the Dendrocrinidae
  • Key to Genera of Dendrocrinidae:
    A. Cup tall and narrow cylindroconical
    I. Infrabasals very tall; radial articular facets narrow, horseshoe-shaped; round slender arms branching on primibrachs 4-5; stem transversely round – Bactrocrinites
    II. Infrabasals moderately tall; radial articular facets wider than horseshoe-shaped; arms branching on primibrachs 3 or 4; stem transversely pentagonal – Atractocrinus
    B. Cup moderately wide conical
    I. Infrabasals 3; anals in cup 2 – Alsopocrinus
    II. Infrabasals 5; anals in cup 3 or 4.
    a. Radianal directly below C radial, anal sac very tall cylindrical with plicate plates; arms branching first on primibrachs 5-7 – Dendrocrinus
    b. Radianal obliquely left below C radial; arms many (60 or more), branching first on primibrachs 3 – Grenprisia
    c. Radianal obliquely left below C radial; arms ?few, branching on primibrachs 3 – Esthonocrinus
    III. Cup very minute, plates ill-known, extremely slender long arms, numerous (approximately 60) well separated, branching first on primibrachs 6-9- Parisangulocrinus

Plicodendrocrinus