activity 2 - amphioxus

1. amphioxusamphioxus

2. introduction
Organisms under Subphylum
Cephalochordata:
•Has no distinct head
•But has a notochord that extends to the head part of
the body.

3. introduction:
Amphioxus:
- means “sharp at both ends”
- a living amphioxus is semitransparent but becomes
opaque when immersed in preserving fluids.

4. Amphioxus and the Vertebrates

5. 
No cephalization
No paired sense organs

6. Has notochord that remains throughout life
Has no vertebral column
Notochord

7. Has pharyngeal slits but in large numbers

8. Dorsal, hollow nervous system
No brain or cranium

9. Metameric muscles (myomeres) but extendes to the
anterior tip of the head

10. Two-layered skin – epidermis and dermis
But outer layer is one-cell thick

11. Well-developed circulatory system
Lack blood cells, muscular heart
Pulsating blood vessels

12. Is coelomate
But gretly restricted

13. External morphology of amphioxus

14. MYOMERE
S
•Lie immediately under
the thin skin throughout
the entire length of the
body
•Provide locomotion
MYOSEPT
A• a connective tissue
partition to which
longitudinal muscle bundles
attach
•It separates the myomeres

15. GONAD
S•Visible through the body
wall and bulge into the water-
filled atrium, into which
sperm or eggs are shed
ATRIOPORE
•It is where the excess
water , gametes and
metabolic wastes exits

16. BUCCAL
CIRRI
•Partially strain the water as it enters
the vestibule and monitor it
chemically

17. Dorsal and ventral fin rays:
maintains balance during
locomotion

18. EYESPOT OCELLI
WHEEL
ORGAN
GILL BARS
GILL SLITS

19. GILL SLITS : where water goes through;
where strings of mucus travelling across
them trap tiny food particles
GILL BARS : supports between gill slits
OCELLI : light-sensitive organ; it assist in
orienting the animal as it burrows in the
sand

20. WHEEL ORGAN : retrieves
some of the heavier food particle
that miss the mouth, and it
directs these through the mouth
and into the pharynx along with
the water stream

21. Internal Structure of Amphioxus

24. Parts and Function
Notochord: protects and support the dorsal nerve
cord; serves as the major skeletal support
throughout life
Nerve cord: serves as central nervous system.
Pharynx: passage way for water, food and air.
Atrium: serves as a collecting chamber for
respiratory water that has passed over the gills.

25. Intestine: major site for digestion of food.
Anus: excretion of waste

26. Anterior end

27. Vestibule: collecting chamber for sea water
Oral hood: serves as entrance and storage
Velum: works as valve and filter; surrounds the
mouth
Velar tentacles: prevent undesirable objects from
entering the digestive cavity

29. Amphioxus
spend much
of their time
buried in
gravel or
mud on the
ocean
bottom

30. When feeding, they let the anterior part of the
body project from the surface of the gravel so
that they can filter food particles from water
passing through their gill slits.

31. FEEDING:

32. Once the food is in the pharynx it is processed as
follows.
Feeding:
Hypobranchial
groove or
endostyle
Epibranchial
groove

36. They burrow into
sand using
rapid
movements of
the body
The continuity of
the notochord
to the very tip
of the rostrum
may be an
adaptation for
burrowing in
sand.

37. The animals swim by contracting the muscle
blocks, or myomeres, that run from end to
end on each side of the body.

38. The blocks on each side are staggered,
producing a side-to-side movement of the
body when swimming.