Page 310 - Introduction to Paleobiology and The Fossil Record

Chapter 12

Spiralians 1: lophophorates

Key points

• Three spiralian invertebrate groups have lophophores, a fi lamentous feeding organ:
brachiopods, bryozoans and phoronids.
• Brachiopods are twin-valved shellfish, with a lophophore and usually a pedicle, adapted

to a wide range of life strategies on the seafl oor.
• The phylum Brachiopoda is currently divided into the linguliformeans, with organo-
phosphatic shells, and the craniiformeans and rhynchonelliformeans, both with calcare-
ous shells.
• Paleozoic communities were dominated by orthides and strophomenides, together with
a variety of spire-bearing forms; rhynchonellides and terebratulides are typical of the
lower-diversity post-Paleozoic brachiopod assemblages.
• Brachiopods dominated the filter-feeding benthos of the Paleozoic but never fully recov-

ered in abundance or diversity from losses during the end-Permian mass extinction.
• Living brachiopods are relatively rare, occupying mostly cryptic and deep-water
habitats.
• Bryozoans are colonial invertebrates with lophophores, commonly displaying marked
non-genetic variation across a wide range of environments.
• The Stenolaemata dominated Paleozoic bryozoan faunas, with only the cyclostomes
surviving the combined effects of the end-Permian and end-Triassic mass extinctions; as
the cyclostomes continued to decline after the end-Cretaceous extinction event, the
cheilostomes radiated to dominate Cenozoic assemblages.

We may consider here under the name Molluscoidea, the two groups of animals which
are known respectively as the Polyzoa [Bryozoa] and the Brachiopoda. These two

groups, in many respects closely allied to one another, present affinities on the one
hand to the Worms and on the other hand to the Mollusca . . .
R.A. Nicholson and R. Lydekker (1890) Manual of Palaeontology, 3rd edn