Urochordata

1. UROCHORDATA
Anatomy of the Sea Squirt
CLASSIFICATION
Kingdom: Animalia
Phylum: Chordata
Subphylum: Urochordata (Tunicates)
Class: Ascidiacea (Sea Squirts)
Larvacea (Larvaceans)
Thaliacea (Thaliaceans)

3. GENERAL CHARACTERISTICS
-Protochordates
•Morphological features: notochord, dorsal
hollow central nervous system, pharynx with
paired pouches; muscular, post-anal tail
-Group of marine chordates in which the
notochord is confined to the locomotor tail of
the larval stage

4. GENERAL CHARACTERISTICS
-Also known as Tunicates
-Enclosed in a delicate, nonliving, and
sometimes beautifully colored transparent tunic
-Filter-feeders.

5. CLASS ASCIDIACEA
→ largest class of urochordates
→ free-swimming larval stage
→ sessile as adults, either solitary or colonial

6. LARVAL STAGE
- Body consists of trunk
containing the immature
viscera and a muscular
notochord-supported tail.
- The nervous system
consists of a dorsal hollow
nerve cord, several
ganglia and nerves
- Respiratory water enters
the atrium chamber which
is then ejected through
the atriopore.
- At metamorphosis, the
notochord is resorbed and
becomes a source of
nutrients and
rearrangement of the
viscera takes place.

7. METAMORPHOSIS

8. - Incoming water current becomes
trapped in the mucus, then the cilia
and esophageal papillae sweep the
mucus and entrap food particles into
the stomach.
- Respiratory water passes over the
gills and into the atrium, a fluid-filled
collecting chamber surrounding the
pharynx. Gas exchange occurs as
water circulates with the help of the
atrial muscles.
- One blood vessel from the heart
runs anteriorly under the endostyle,
and another runs posteriorly to the
digestive organs and gonads.
- Gametes may be shed through the
excurrent siphon for external
fertilization or eggs are retained for
fertilization and early development.
ADULT

9. GARSTRANG’S HYPOTHESIS

10. UROCHORDATA
Anatomy of the Sea Squirt