activity 2 - amphioxus
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Transcript of activity 2 - amphioxus
amphioxusamphioxus
Introduction
Organisms under Subphylum Cephalochordata:
• Has no distinct head
• But has a notochord that extends to the head part of the body.
Introduction:
Amphioxus:
- means “sharp at both ends”
- a living amphioxus is semitransparent but becomes opaque when immersed in preserving fluids.
Amphioxus and the Vertebrates
No cephalizationNo paired sense organs
Has notochord that remains throughout lifeHas no vertebral column
Notochord
Has pharyngeal slits but in large numbers
Dorsal, hollow nervous systemNo brain or cranium
Metameric muscles (myomeres) but extendes to the anterior tip of the head
Two-layered skin – epidermis and dermisBut outer layer is one-cell thick
Well-developed circulatory systemLack blood cells, muscular heart
Pulsating blood vessels
Is coelomateBut gretly restricted
External morphology of amphioxus
MYOMERES
•Lie immediately under the thin skin throughout the entire length of the body
•Provide locomotion
MYOSEPTA• a connective tissue partition to which longitudinal muscle bundles attach •It separates the myomeres
GONADS•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
BUCCAL CIRRI
•Partially strain the water as it enters the vestibule and monitor it chemically
Dorsal and ventral fin rays: maintains balance during locomotion
EYESPOT OCELLI
WHEEL ORGAN
GILL BARS
GILL SLITS
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
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
Internal Structure of Amphioxus
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.
Intestine: major site for digestion of food.
Anus: excretion of waste
Anterior end
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
Amphioxus spend much of their time buried in gravel or mud on the ocean bottom
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.
FEEDING:
Once the food is in the pharynx it is processed as follows.
Feeding:
Hypobranchial groove or endostyle
Hypobranchial groove or endostyle
Epibranchial groove
Epibranchial groove
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.
The animals swim by contracting the muscle blocks, or myomeres, that run from end to end on each side of the body.
The blocks on each side are staggered, producing a side-to-side movement of the body when swimming.