| These are broad concavities in the ambitus that could be considered precursors to the ambulacral notches of certain mellitids. |
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| For each individual, 2 diameters were recorded across the ambitus and averaged. |
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| Notches are ambulacral lunules that form close enough to the ambitus that the ambitus is unable to close over the distal part of the notch to form a closed lunule. |
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| Test diameter was measured at 2 perpendicular points across the ambitus using calipers, and individuals were weighed to the nearest milligram. |
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| At ordinal levels, in cassiduloids and holectypoids, ambitus is circular, elliptical or oval, while clypeasteroids have a pentagonal to circular type. |
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