ABSTRACT
So let us switch to the fixosessile Pelmetozoa. In the Paleozoic they comprised more classes than all extant echinoderms together and in the shallow seas of the Mesozoic they were still common enough to locally become rock-forming. In the present seas, this wealth is reduced to one clade, the crinoids. To observe their more representative examples we need a submersible, because only in the lightless refuge of the deep sea do the once thriving stemmed crinoids persist. These “living fossils” serve as a model for the reconstruction of extinct forms; but as in modeling ammonites after living Nautilus, we should be aware of potential limits to such comparisons.
