The Prechordates
• Phyla that have some chordate features but
not all
• Considered to be possible ancestors to the
phylum Chordata
Phylum Chaetognatha
Arrow worms
• Approximately 70
species; 1-10 cm long
• All marine, freeliving, planktonic
• bilaterally
symmetrical, as are
all of the rest of the
phyla
Phylum Chaetognatha
Arrow worms
• body of three
regions: head,
trunk, tail
• has lateral and
caudal fins
• has
circumesophogeal
ganglia
Phylum Chaetognatha
Arrow worms
• no circulatory
system, excretory
system, respiratory
• skeleton is
hydrostatic type
• are hermaphroditic;
with crossfertilization, and
internal
• are carnivorous predators of
plankton
Phylum Hemichordata
(the acorn worms)
• about 100 species, all
marine, 0.5 cm - 2 m
• benthic (live on the
bottom) and free
living
• solitary or colonial
• vermiform- elongate
Phylum Hemichordata
(the acorn worms)
• body in three
parts;
proboscis,
collar and
trunk
• are gill slits for
respiration
• no post-anal
tail
Phylum Hemichordata
(the acorn worms)
• have free
living larvae
called
tornaria
• Resemble
echinoderm
larvae
Phylum Hemichordata
(the acorn worms)
• primarily feeding
on detritus and
microscopic
organisms
• have circulatory
system; two main
blood vessels and a
central sinus
(heart)
• sexes are separate;
fertilization is
external