1. ACTIVITY #1
Agra
Dullano
Fernandez
Pacudan

2. Larval Structure of Sea Squirt

6. Sea Squirt Metamorphosis

7. In the case of the ascidians these features
disappear in adult life when the larvae pass
through metamorphosis and most of the
chordate features are lost.
After the metamorphosis, the ascidians'
larval stage is more biologically complex than
the adult form of the animal.

8. Metamorphosis starts when the tunicate
finds a suitable rock/coral to affix to and
cements itself in place.
When they undergo metamorphosis, they
lose their tail and other vertebrate
characteristics. The remainder of the body twists
through 180 degrees in order to become a small
tunicate.

9. What are the parts that are lost during
metamorphosis?
Notochord
Tail
hollow neural tube running along the body
(cerebral ganglion)
Sensory vesicle
Ocellus
statolith

11. What are the parts that developed during
metamorphosis?
₰ Nervous system
₰ Viscera
₰ Incurrent and excurrent siphon
₰ Tunic
₰ Stolon

13. Adult Sea Squirt
External features

14. • Tunic – acts as a kind of exoskeleton that protects
the internal organs of the sea squirt
▫ Contains blood vessels and scattered cells
▫ This may be smooth, spiny or hairy for
defense
• Stolon/Base – is the point of attachment of a
sessile adult to a permanent substrate

15. • Incurrent siphon – originated from the larval
mouth
▫ Food particles come in along with the incoming
water stream
• Excurrent siphon – originated from the
atriopore
▫ Expels digestive wastes, gametes and the feeding
current carried out of the atrium

17. Internal features

18. Digestive System
• Pharynx – acts as a sieve for food
▫ Food particles are trapped
▫ Collects food, oxygen, and water then
slowly ingests it
• Endostyle – a groove in the pharynx that
secretes mucus(movement is caused by action of
cilia) that traps food particles and conveys them
into the digestive tract

19. • Oesophagus – passageway of food particles
towards the stomach
• Stomach – where the entrapped food particles
from the endostyle go and become
digested, after being swept by cilia and
oesophageal papillae (found in the oesophagus)

20. • Intestine – food from the stomach passes
through and emerges into the anus
• Anus – where the digestive wastes pass through
and are expelled out through the excurrent
siphon

21. Nervous system
• Cerebral ganglion – serves as a primitive
brain

22. Reproductive system
• Gonads – are hermaphroditic and consist of
ovary and testis on each side
• Genital ducts – sperm and egg cells are
discharged separately towards the excurrent
siphon

23. Circulatory system
• Atrium – a fluid filled collecting chamber
surrounding the pharynx
▫ Where atrial muscles pumped out and
discharged the deoxygenated water to
the exterior via the excurrent siphon
• Heart – where blood is pumped alternately
forward for a few beats, then backward, pausing
before reversing the flow.

24. Digestive Process
Ascidiacea

25. Digestive Process
• Water, along with any food particles (mainly
plankton) it contains enters the incurrent
siphon.
• Mucus, secreted by the endostyle, traps food
particles as water is pushed out of the gill slits.
• Food passes through the oesophagus and into
the stomach

26. Digestive Process
• The stomach secretes enzymes that digest the
food.
• Digested material travels through the intestine,
which opens up at a cloaca at the base of the
excurrent siphon.

27. Pathway
Water Incurrent
(w/ food particles) Siphon
Pharynx
Oesophagus
Stomach Water
(through
Intestine body cavity)
Cloaca
Water Excurrent
(w/ excretions) Siphon