The Lophophorates

A.  The Lophophorates--Characteristics
     1.  U-shaped circle of tentacles with mouth at center and
          anus at side
     2.  U-shaped digestive tract
     3.  Typically eucoelomate, with a deuterostomate-type of
          structure with respect to the origin of the coelom
B.  The Lophophorates--Groups
     1.  Phoronida
          a.  Worm like creatures living in the deep-sea
          b.  Coelom is definitely tri-partite
          c.  Worms are small, usually less than centimeter in 
               diameter and less than 100 cm long
     2.  Brachiopods
          a.  Consist of two groups, inarticulate and articulate.
               These groups are differentiated by presence or 
               absence of hinge articulation.  Both groups have a
               fleshy-like structure called a pedicel that passes
               from the shell into the substrate.  The shell is
               composed of calcium phosphate which differs from
               from the calcium carbonate of mollusks.
          b.  An ancient group present at the Cambrian explosion.
               Some thoughts are that the group has been 
               out-competed by the bivalves.  The group has been
               pushed into marginal or deeper water environments.
          c.  Some of the articulate brachiopods in the Paleozoic 
               were highly ornamented, with spines, etc.
          d.  The organism used its lophophore as a filter device
               Many only have mouth and no anus.  
     3.  Ectoprocta or Bryozoa--The moss animals
          a.  Consist of polypoid individuals (zooids) that are in
               a colony.  Typically each zooid lives in a calcarous
               "house" that is attached to other zooids.  
          b.  Uses the pressure of fluids in the space between
               the zooid and its container to push lophophore out.
               Muscles pull the lophophore back in.  
          c.  Colony has more than one type of zooid.
C.  Where does this group fit into the exisiting arrangement of 
      groups?
     1.  One hypothesis has the lophophorate groups related to the
          deuterostomes, perhaps to some basal group that was 
          ancestral to both groups.
     2.  Another hypothesis puts them into a separate and distinct
          group from both the protostomes and the deuterostomes,
          perhaps in between the two groups.
     3.  Some features, eg., the coelomic arrangements in the 
          phoronids, demonstrate close connections to the deutero-
          stomes.  Other features, such as larval structures
          may indicate a protostomate heritage.