gives support to the body and maintain its shape. It permits slight bending movement of the body
myotomes
responsible for a significant number of the body's motor functions
cirri
act as sensory devices and as a filter for the water passing into the body
Gill slits
Functions as a filter feeding device
Oral hood atriopore
serves as entrance and storage of food serves as exit passage of water
Metapleural folds
help to stabilize the lancelet while swimming
Caudal fin
used for propulsion and steering
Dorsal fin
stabilize the animal against rolling and to assist in sudden turns
anus
Excretion of waste
Wheel organ
draws food through the use of its cilia for digestion
Ocelli
act as simple eyes to detect light
Velar tentacles
prevent undesirable objects from entering the digestive cavity
velum
work as valve and filter; surrounds the mouth
atrium
Surrounds the pharynx; where water enters
cecum
Functions for secretion and absorption
1. What are the generalized features of chordates seen in amphioxus?
In common with vertebrates, lancelets have a hollow nerve cord running along the back, pharyngeal slits and a tail that runs past the anus. Also like vertebrates, the muscles are arranged in blocks called myomeres. 2. What are the other charachteristics shared by amphioxus and vertebrates?
Other similar characteristics include dorsal and ventral aortas and branchial (gill) arches (blood vessels running over the gills). 3. What makes amphioxus distinct from vertebrates?
Unlike vertebrates, the dorsal nerve cord is not p rotected by bone but by a simpler notochord made up of a cylinder of cells that are closely packed to form a toughened rod. The lancelet notochord, unlike the vertebrate spine, extends into the head. The nerve cord is only slightly larger in the head region than in the rest of the body, so that lancelets cannot be said to possess a true brain. Neither do they have any eyes, or other complex sense organs comparable to those of vertebrates. Amphioxus also lack tripartite brain (with forebrain, midbrain and hindbrain) protected by a skull, chambered heart, closed circulatory system and neural crest found on the embryonic neural tube and are engaged in the formation of the cranium, tooth dentine, some endocrine glands and Schwann cells, which provide myelin insulation to nerve cells).
References:
Romer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia, PA: HoltSaunders International. pp. 18–21. ISBN 0-03-910284-X.
