Differentiate between the 3 classes of urochordate
Answer:
Urochordates or Tunicata are devided into 3 classes:
1. Ascidiacea
2. Larvacea
3. Thaliacea
Ascidiace
Larvacea
Thaliacea
Fixed or free swimming. Free swimming
Free swimming and pelagic
Solitary or colonial
Body is saccular. Tail is absent Tail is present throughout Body is cask shaped with
their life
opening at the opposite ends.
Tail is absent in the adult
The body is covered by a test
True test covering is lacking
The body is covered by
transparent test.
Atrium is present
Atrium is absent
Atrium is present
Pharynx is large and contains Two gill slits are present
Pharynx is small. Gill-slits
numerous
gill
slits
or
number is less.
stigmata, opening into the
atrial cavity
Notochord and nerve-cord are Notochord and nerve cord are Notochord and nerve-cord are
absent
persistent
absent in the adult
The dorsal lamina is present
The dorsal lamina is absent
The dorsal lamina is present
The test is secreted by the The test is not permanent and The test is permanent
body wall of the adult animal is secreted at times only
Reproduction is both asexual Only sexual reproduction is They exhibit alteration of
and sexual. These are bisexual known.
They
are generation by reproducing
animals
hermaphrodite and there is sexual and asexual forms.
no
metamorphosis
in These are bisexual animals
development
Life-history includes a typical They are neotenic forms i.e. Tailed larva may be present or
tadpole larva that is free larval nature is retained absent
swimming
with
well throughout life.
developed tail and possesses
well developed dorsal tubular
nerve chord