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Ristnacrinus
Classification
Phylum:
Echinodermata
Subphylum:
Crinozoa
Class:
Crinoidea
Subclass:
Inadunata
Order:
Disparida
Suborder:
Disparida
Superfamily:
Myelodactylacea
Family:
Eustenocrinidae
Formal Genus Name and Reference:
Ristnacrinus ÖPIK, 1934, p. 3
Type Species:
R. marinus, OD
Images
(Click to enlarge in a new window)
Fig. 348, 1. *R. marinus, 1 a, E-ray view of crown and stem, x2, 1 b, C-ray view of cup and proximal arms, x2.9 (Öpik, 1934).
Synonyms
Geographic Distribution
Eu. (Est.)
Age Range
Beginning Stage in Treatise Usage:
M.Ord. (Caradoc, )
Beginning International Stage:
Sandbian
Fraction Up In Beginning Stage:
0
Beginning Date:
458.18
Ending Stage in Treatise Usage:
M.Ord. (Caradoc, )
Ending International Stage:
Katian
Fraction Up In Ending Stage:
66.7
Ending Date:
447.72
Description
Cup high conical, truncate below, basals fused with proximal columnal or absent, not visible, large quadrate inferradials present in each ray supporting smaller superradials above, that of C ray next below small anal X and succeeding anal sac plates on left side and large primibrach on right. Primibrachs 1 axillary in B, D, and E rays, primibrachs 2 axillary in A and C rays, brachials not fixed in cup. Arms strongly rounded, branching at least twice isotomously. Stem transversely round, composed of thin and thick columnals, latter with bifascial articular surfaces.
References
Museum or Author Information
Classification
Phylum:
Echinodermata
Subphylum:
Crinozoa
Class:
Crinoidea
Subclass:
Inadunata
Order:
Disparida
Suborder:
Disparida
Superfamily:
Myelodactylacea
Family:
Eustenocrinidae
Formal Genus Name and Reference:
Ristnacrinus ÖPIK, 1934, p. 3
Type Species:
R. marinus, OD
Images
(Click to enlarge in a new window)
Fig. 348, 1. *R. marinus, 1 a, E-ray view of crown and stem, x2, 1 b, C-ray view of cup and proximal arms, x2.9 (Öpik, 1934).
Synonyms
Geographic Distribution
Eu. (Est.)
Age Range
Beginning Stage in Treatise Usage:
M.Ord. (Caradoc, )
Beginning International Stage:
Sandbian
Fraction Up In Beginning Stage:
0
Beginning Date:
458.18
Ending Stage in Treatise Usage:
M.Ord. (Caradoc, )
Ending International Stage:
Katian
Fraction Up In Ending Stage:
66.7
Ending Date:
447.72
Description
Cup high conical, truncate below, basals fused with proximal columnal or absent, not visible, large quadrate inferradials present in each ray supporting smaller superradials above, that of C ray next below small anal X and succeeding anal sac plates on left side and large primibrach on right. Primibrachs 1 axillary in B, D, and E rays, primibrachs 2 axillary in A and C rays, brachials not fixed in cup. Arms strongly rounded, branching at least twice isotomously. Stem transversely round, composed of thin and thick columnals, latter with bifascial articular surfaces.