It burrows in
the loose bottom, or lies in it with its large compound eyes
peeping out in search of prey. It is the chief representative of
the hard-cased group (Crustacea) which will later replace it with
the lobster, the shrimp, the crab, and the water-flea. Its
remains form from a third to a fourth of all the buried Cambrian
skeletons. With it, swimming in the water, are smaller members of
the same family, which come nearer to our familiar small
Crustacea.
Shell-fish are the next most conspicuous inhabitants. Molluscs
are already well represented, but the more numerous are the more
elementary Brachiopods ("lampshells"), which come next to the
Trilobites in number and variety. Worms (or Annelids) wind in and
out of the mud, leaving their tracks and tubes for later ages.
Strange ball or cup-shaped little animals, with a hard frame,
mounted on stony stalks and waving irregular arms to draw in the
food-bearing water, are the earliest representatives of the
Echinoderms. Some of these Cystids will presently blossom into
the wonderful sea-lily population of the next age, some are
already quitting their stalks, to become the free-moving
star-fish, of which a primitive specimen has been found in the
later Cambrian.
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