Download Invertebrate Chordates

Invertebrate Chordates
CHORDATES ARE ANIMALS THAT ARE
CHARACTERIZED BY A NOTOCHORD, A
HOLLOW DORSAL NERVE CORD, AND
PHARYNGEAL THROAT SLITS.
Notochord:
y A long flexible supporting rod that runs through at
least part of the body – usually along the dorsal
surface just beneath the nerve cord. Present usually
early in development to be replaced by a backbone in
vertebrates.
Hollow Dorsal Nerve Cord:
y Runs along the dorsal surface just above the
notochord (in most invertebrates nerve cords run
along the ventral surface). Nerves leave this cord at
regular intervals to connect with organs, muscles,
and sense organs. The front end of the cord, in most
chordates, develops into a brain.
Pharyngeal slits:
y Paired structures in the throat region of the body. In
aquatic chordates – lancets and fishes – these are gill
slits. Many invertebrates have gills of some sort in
various places whereas terrestrial chordates that use
lungs for respiration, have pharyngeal slits for a brief
period of time during the development of the
embryo.
Tunicates:
y Small marine chordates that eat plankton that they
filter from the water. Only the tadpole-shaped larvae
of tunicates have a notochord and a dorsal nerve
cord that leave when the animal undergoes
metamorphosis to become sessile, attach to the floor,
and live in colonies. These animals filter feed and
breathe at the same time through a pharyngeal
basket pierced by gill slits.
Lancelets:
y Live in the sandy body of shallow tropical oceans.
They are fishlike with a definite head.
y Feeding – pass water through their pharynx where
food gets stuck in mucus. This mucus is then
swallowed into the digestive tract that passes straight
to the anus near the tail. Lancelets have no jaw.
y Respiration – they have a mouth that opens to a long
pharyngeal region with up to 100 pairs of gill slits.
Lancelets Con’t:
y Vascular system – Simple primitive heart that
pumps blood through vessels in a closed circulatory
system. Show evidence of segmentation as their
muscles are organized into V – shaped units that are
on either side of the body. Each unit receives a
branch from the main nerve cord. This segmented
nerve and muscle organization is found in all living
vertebrates.
y Movement – they have no appendages and move by
bending their bodies back and forth.