Echinoderms and Chordates

A.  Characteristics of Echinoderms
     1.  tube feet
     2.  pentamerous radial symmetry
     3.  endoskeleton of calcareous plates
     4.  coelom forms by enterocoelous means
     5.  coelom is tripartite, i.e., three separate compartments
B.  Groups of Echinoderms
     1.  Asteroidea
          a.  Central disk not differentiated from arms
          b.  Typically five or pattern of five arms
     2.  Ophiuroidea-brittle stars
          a.  Central disk distinct from arms
          b.  Arms long and slender, break-off easily
     3.  Echinoidea--urchins and sand dollars
          a.  Lack arms, but still have pentamerous symmetry
          b.  Have feeding structure called Aristotle's lantern
               Structure has five teeth that are used for grazing
               on micro and macroscopic algae
     4.  Crinoidea-sea lillys
          a.  Have arms, often branched that are used for filter
               feeding
          b.  Typically have "vase" shaped body that sits atop a
               long stem consisting of many ossicles
          c.  Typically sedentary, although they can move by 
               "beating" arms
     5.  Holothuroidea-sea cucumbers
          a.  Have pentamerous symmetry, but body is elongated 
               along dorsal ventral axis.
          b.  Skeleton much reduced consisting of small ossicles
               embedded in body wall
C.  The Chordates--Characteristics
     1.  Dorsal hollow nerve cord
     2.  Dorsal notochord
     3.  Paired pharyngeal gill-slits
     4.  Post-anal tail
     5.  Ventral heart
D.  The Chordates--The Non-vertebrate members
     1.  Hemichordates
          a.  Often included in their own phylum.
          b.  Have structures that are typically chordate structures
               eg., paired pharyngeal gill-slits, 
          c.  Other structures are like, but not exactly true 
               chordate structures, eg, nerve cord and notochord
          d.  Distinquishing characteristic is the proboscis and
               the collar in the acorn worms, and the tentacles on
               the Enteropneusts
     2.  The chordate invertebrates
          a.  Urochordata--sea squirts, etc.  As adults very much
               unlike chordates, i.e., only have gill slits.  Have
               a test of cellulose that covers over body.  Larval
               stage has all the characteristics
          b.  Larvacea--tad-pole like creatures that look very much
               like the larval stages of the above group.  Have all
               the characteristics
          c.  Cephalochordata--Sea lancelets.  The most vertebrate-
               like of the non-vertebrate chordates.  Body fusiform
               with distinct gill slits, notochord, nerve cord and 
               post anal tail.  
          b.  All the above groups are marine.
E.  How can we make the connections between the Chordates and the 
     Echinoderms?
     1.  Can't base it on adult features.  Adults of both groups
          are radically different.  The feature of tube feet, 
          spines, pentamerous symmetry, etc. make it impossible to
          associate the two groups
     2.  The one commonality is with the larval stages.  The common
          larvae is called a dipleurula larvae.  It is a bilaterally
          symmetrical organism with a complete gut and a ciliary
          band that is used for locomotion.  The actual stage in the
          hemichordates is called a tornaria larvae.