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TF0903 - Irregular Echinoid
Location
Upper Chalk, Weston Colville, Cambridgeshire
Species
Praecursor
Stratigraphic Range
Cretaceous
Taxonomy
Phylum: Echinodermata
Class: Echinoidea
Subclass: Irregularia
Order: Spatangoida
Genus: Micraster
Class: Echinoidea
Subclass: Irregularia
Order: Spatangoida
Genus: Micraster
Distinctive Features
Bilateral symmetry
Five radial ambulacra
Peristome (opening for mouth) and periproct (opening for anus) migrated
Spine attachment scars
Five radial ambulacra
Peristome (opening for mouth) and periproct (opening for anus) migrated
Spine attachment scars
Preservation
Sediment infil
Shell mineral replacement
Disarticulation of spines
Shell mineral replacement
Disarticulation of spines
Advanced notes
Note the streamlined shape for burrowing through the sediment, and how the ambulacra, which bear the tube feet, do not continue onto the underside of the animal where the mouth is.
This is because the tube feet are used for respiration but not for movement, for which small spines are used.
This is because the tube feet are used for respiration but not for movement, for which small spines are used.