HEMICHORDATES
The Half Chordates
GENERAL CHARACTERISTICS
1. bilaterally symmetrical
2. more than two cell layers
3. has tissues and organs
4. true coelom
5. possesses a through gut with an anus
6. diffuse nervous system
7. partially open circulatory system
8. glomerulus as excretory organ
9. sexual reproduction
10. marine lifestyle
DISTINCT CHARACTERISTICS
Tripartite division of the body into the proboscis, collar and trunk
ECHINODERMS HEMICHORDATES CHORDATES
Ciliated larval stage
Pharynx with multiple gill slits
SIMILARITIES Dorsal nerve cord
Ventral blood vessel
Bilateral symmetry
Gill slits
Notochord
Pentameral
Stomochord (precursor Post-anal tail
symmetry
DIFFERENCES to notochord) In
Water vascular
Mesocoelomic cord vertebrates:
system
Bony
, RELATIONSHIP WITH OTHER PHYLA
A. TRADITIONAL (based on morphological characteristics)
B. CALCICHORDATE (based on Jefferies’ Calcichordate Hypothesis)
C. MOLECULAR (DNA evidence; currently most accepted)
ORGANIZATION- MODE OF LIFE
COLONIAL
Zooids are the individual graptolite or pterobranch individuals
The colony is called a rhabdosome.
POLYMORPHISM
Budding zooids secrete the skeleton
Feeding zooids gather food and carry out sexual reproduction
There are also three types of theca: autotheca, bitheca and stolotheca
The Half Chordates
GENERAL CHARACTERISTICS
1. bilaterally symmetrical
2. more than two cell layers
3. has tissues and organs
4. true coelom
5. possesses a through gut with an anus
6. diffuse nervous system
7. partially open circulatory system
8. glomerulus as excretory organ
9. sexual reproduction
10. marine lifestyle
DISTINCT CHARACTERISTICS
Tripartite division of the body into the proboscis, collar and trunk
ECHINODERMS HEMICHORDATES CHORDATES
Ciliated larval stage
Pharynx with multiple gill slits
SIMILARITIES Dorsal nerve cord
Ventral blood vessel
Bilateral symmetry
Gill slits
Notochord
Pentameral
Stomochord (precursor Post-anal tail
symmetry
DIFFERENCES to notochord) In
Water vascular
Mesocoelomic cord vertebrates:
system
Bony
, RELATIONSHIP WITH OTHER PHYLA
A. TRADITIONAL (based on morphological characteristics)
B. CALCICHORDATE (based on Jefferies’ Calcichordate Hypothesis)
C. MOLECULAR (DNA evidence; currently most accepted)
ORGANIZATION- MODE OF LIFE
COLONIAL
Zooids are the individual graptolite or pterobranch individuals
The colony is called a rhabdosome.
POLYMORPHISM
Budding zooids secrete the skeleton
Feeding zooids gather food and carry out sexual reproduction
There are also three types of theca: autotheca, bitheca and stolotheca
