The Burgess Shale - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 38

MarrellaPhylum Arthropoda
A small, feathery arthropod, often known
as the 'lace-crab', it is the most common
Burgess animal, with over 15,000
specimens discovered, yet it is known from
no other Cambrian deposit ( 39, 40 ). It was
the first to be discovered by Walcott
and the first to be redescribed by
Whittington. A head shield has two pairs of
curving spines, while the head has
two pairs of antennae. The 20 body
segments each bear a pair of identical legs,
suggesting that it is a primitive arthropod
and could be ancestral to the three
major groups of aquatic arthropods
(crustaceans, trilobites, chelicerates; see
Whittington, 1971).

known animal ( 37 , 38 ). This was partly
because it had been reconstructed upside-
down, standing on rigid spines and waving
its tentacles in the water. Additional
specimens suggested reversing this
interpretation and suddenly it was
apparent that this genus was a marine
velvet worm, a caterpillar-like group called
the lobopodians ('lobed feet').
Hallucigenia crawled on its fleshy limbs
and used its spines for protection as it
scavenged for decaying food. Aysheaia is
another such Burgess lobopod (see
Conway Morris, 1977b).

39

39 The arthropod Marrella
splendensMM. Length
20 mm 0.8 in.

40

40 Reconstruction of
Marrella.