The Trilobite, once the master of the seas, slowly
yields to the stronger competitors, and the latter part of the
Carboniferous period sees the last genus of Trilobites finally
extinguished. The Eurypterids (large scorpion-like Crustacea,
several feet long) suffer equally, and are represented by a few
lingering species. The stress favours the development of new and
more highly organised Crustacea. One is the Limulus or
"king-crab," which seems to be a descendant, or near relative, of
the Trilobite, and has survived until modern times. Others
announce the coming of the long-tailed Crustacea, of the lobster
and shrimp type. They had primitive representatives in the
earlier periods, but seem to have been overshadowed by the
Trilobites and Eurypterids. As these in turn are crushed, the
more highly organised Malacostraca take the lead, and primitive
specimens of the shrimp and lobster make their appearance.
The Echinoderms are still mainly represented by the sea-lilies.
The rocks which are composed of their remains show that vast
areas of the sea-floor must have been covered with groves of
sea-lilies, bending on their long, flexible stalks and waving
their great flower-like arms in the water to attract food.
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