CHORDATA
GENERAL CHARACTERISTICS
- possesses the following (for at least some period of their life cycle):
- notochord - a cartilaginous rod running underneath and supporting the nerve
cord
- dorsal nerve cord - a bundle of nerve fibers which runs down the "back" and
connects the brain with the lateral muscles and other organs
- pharyngeal slits - a series of openings that connect the inside of the throat to
the outside of the "neck", often but not always used as gills
- post-anal tail - an extension of the body past the anal opening
DISTINCT CHARACTERISTICS
, A. TRADITIONAL (based on morphological characteristics)
B. CALCICHORDATE (based on Jefferies’ Calcichordate Hypothesis)
C. MOLECULAR (DNA evidence; currently most accepted)
HEMICHORDATES CHORDATES
Pharynx with multiple gill slits
Dorsal nerve cord
SIMILARITIES Ventral blood vessel
Bilateral symmetry
Gill slits
Notochord
Stomochord (precursor Post-anal tail
DIFFERENCES to notochord) In
Mesocoelomic cord vertebrates:
Bony
PHYLUM CHORDATA
Vetulicolians
Calcichordates
Urochordates
Cephalochordates
Conodonts
,VETULICOLIANS (AND YUNNANOZOONS)
- “sausage balloons”
- knotted in the middle: bulbous sections sandwiching a flexible connection
- large mouth with strengthened rim and guts
- five circular structures: gill slits
- Early to Middle Cambrian
- From their general form, it is assumed that all vetulicolians discovered thus far
were swimming animals that spent much, if not all, of their time living in the water
column
- From their mouths, which had no features for chewing or grasping, it is
automatically assumed that they were not predators
- From their gill slits, many researchers regard the vetulicolians as being
planktivores
CALCICHORDATES
- includes stylophorans and carpoids
- asymmetrical organisms having a calcitic outer skeleton pierced by numerous
holes
- compact body portion and a long-segmented appendage
- Middle Cambrian to Middle Devonian
PROBLEMS
- morphological and phylogenetic analyses do not correspond to requirements
- much hypothesis dependent on disputed anatomical structures
- calcite skeleton of carpoids and echinoderms was lost three times on the lines of
cephalochordates, tunicates and vertebrates
, UROCHORDATES
- includes the tunicates, ascidians, and “sea squirts”
- the name tunicate derives from the cellulose-like carbohydrate material, called
the tunic, which covers the outer body of tunicates
- sessile and suspension feeders: seawater enters the inhalant siphon, through the
pharynx, atrium and exits the exhalant siphon
CEPHALOCHORDATES
- has a well-defined notochord and dorsal nerve chord, ventral blood vessel,
pharyngeal basket, post-anal tail, liver, kidney more advanced nervous system
and many genetic and molecular features unique to them and higher chordates
- represented in modern oceans by the amphioxus or lancelet
GENERAL CHARACTERISTICS
- possesses the following (for at least some period of their life cycle):
- notochord - a cartilaginous rod running underneath and supporting the nerve
cord
- dorsal nerve cord - a bundle of nerve fibers which runs down the "back" and
connects the brain with the lateral muscles and other organs
- pharyngeal slits - a series of openings that connect the inside of the throat to
the outside of the "neck", often but not always used as gills
- post-anal tail - an extension of the body past the anal opening
DISTINCT CHARACTERISTICS
, A. TRADITIONAL (based on morphological characteristics)
B. CALCICHORDATE (based on Jefferies’ Calcichordate Hypothesis)
C. MOLECULAR (DNA evidence; currently most accepted)
HEMICHORDATES CHORDATES
Pharynx with multiple gill slits
Dorsal nerve cord
SIMILARITIES Ventral blood vessel
Bilateral symmetry
Gill slits
Notochord
Stomochord (precursor Post-anal tail
DIFFERENCES to notochord) In
Mesocoelomic cord vertebrates:
Bony
PHYLUM CHORDATA
Vetulicolians
Calcichordates
Urochordates
Cephalochordates
Conodonts
,VETULICOLIANS (AND YUNNANOZOONS)
- “sausage balloons”
- knotted in the middle: bulbous sections sandwiching a flexible connection
- large mouth with strengthened rim and guts
- five circular structures: gill slits
- Early to Middle Cambrian
- From their general form, it is assumed that all vetulicolians discovered thus far
were swimming animals that spent much, if not all, of their time living in the water
column
- From their mouths, which had no features for chewing or grasping, it is
automatically assumed that they were not predators
- From their gill slits, many researchers regard the vetulicolians as being
planktivores
CALCICHORDATES
- includes stylophorans and carpoids
- asymmetrical organisms having a calcitic outer skeleton pierced by numerous
holes
- compact body portion and a long-segmented appendage
- Middle Cambrian to Middle Devonian
PROBLEMS
- morphological and phylogenetic analyses do not correspond to requirements
- much hypothesis dependent on disputed anatomical structures
- calcite skeleton of carpoids and echinoderms was lost three times on the lines of
cephalochordates, tunicates and vertebrates
, UROCHORDATES
- includes the tunicates, ascidians, and “sea squirts”
- the name tunicate derives from the cellulose-like carbohydrate material, called
the tunic, which covers the outer body of tunicates
- sessile and suspension feeders: seawater enters the inhalant siphon, through the
pharynx, atrium and exits the exhalant siphon
CEPHALOCHORDATES
- has a well-defined notochord and dorsal nerve chord, ventral blood vessel,
pharyngeal basket, post-anal tail, liver, kidney more advanced nervous system
and many genetic and molecular features unique to them and higher chordates
- represented in modern oceans by the amphioxus or lancelet
