Activity 1 Sea Squirt

1. ACTIVITY #1 Agra Dullano Fernandez Pacudan

2. Larval Structure of Sea Squirt

3. Sea Squirt Metamorphosis

4. 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.

5. 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.

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

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

8. Adult Sea Squirt External features

9. 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

10. 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

11. Internal features

12. 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

13. 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)

14. 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

15. Nervous system Cerebral ganglion – serves as a primitive brain

16. 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

17. 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.

18. Digestive Process Ascidiacea

19. 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

20. 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 .

21. Pathway Water (through body cavity) Water (w/ food particles) Water (w/ excretions)