ORIGIN OF CHORDATES Flashcards
A large phylum of animals that includes the
vertebrates together with the sea squirts and
lancelets.
Chordates
Chordate is A phylum of animals having at least at some stage of
development (3)
Notochord
Dorsally situated CNS
Gill slits
The chordate evolved during what period
Cambrian
Chordate Evolved during the Cambrian period from a __ ancestors (__,__)
Deuterostome
Echinoderm
Hemichordates
Chordate origin was proposed by a French zoologist __
Geoffrey Saint Hilaire
Chordate body plan was
derived from a turned-over
version of
Annelid
He enumerated several
criticisms/differences that
surpass similarities (chordate origin)
Georges Cuvier
Segmentation of annelid is _ to _
Skin
Gut
Type of cleavage in annelids
Spiral cleavage
Type of cleavage in vertebrates
Radial cleavage
Annleids are protostome/deuterostome
Protostomes
Vertebrates are protostomes/deuterostomes
Deuterostomes
Known as the first mouth in chordate phylogeny
Protostomes
Known as the second mouth in chordate phylogeny
Deuterostomes
Proposed that echinoderm
larvae gave rise to chordates
by neoteny
Johannes Muller (1860)
Refers to the retention of
juvenile features in the adult
animal
Neoteny
__ are also
deuterostomes and possess
mesodermal skeletal elements
(made from CaCO3
).
Echinoderms
__ is a small fossil group of echinoderms with
skeleton similar to that echinoderm with a tail similar to the
stalk of crinoid proposed to be a link between echinoderms
and vertebrates
Calcichordate
Hemichordate origin
suggested that ancestral
deuterostomes were
sedentary tentacle feeders
whose mucous-laden
ciliated tentacles served to
trap planktons as they were
waved in water (like modern
hemichordates).
Romer (1959)
Calcichordate fossil
Echinoderm origin
Hemichordate fossil
Acorn worm
Balanoglossus
Hemichordate origin
Urochordate origin
__ and __ tadpole-like
larva of urochordates which
carries typical chordate
characters.
W. Garstang (1928)
Berrill (1955)
suggested
that chordates evolved from
some sessile filter-feeding
urochordate by the larval
stage evolving into adult by
neoteny and by losing the
sedentary adult stage
W. Garstang (1928)
Tunicate adult
Tunicate larva
Urochordate origin
primitive and advanced
characters of
cephalochordates possess
all chordate characters in
typical state
(Theory and person)
Cephalochordate origin
Chamberlain (1900)
Pikaia gracilens fossil
Modern amphioxus
Cephalochordate origin
proposed that the common
ancestor of echinoderms and
chordates was a sessile ciliary
arm feeder that lived in the
plankton-rich environment of
the Cambrian.
* Later evolved in a free
swimming form at a time of
food scarcity.
(Theory and author)
Combined theory
E.J.W Barrington (1965)
Yuknessia
Pikaia gracilens
Combined theory
(4) structures of a chordate
Dorsal hallow nerve cord
❑Notochord
❑Pharyngeal pouches/slits
❑Postanal Tail
Dorsally located.
* Nerves are branched to this
cord at regular intervals and
connect to internal organs,
muscles, and sense organ.
Hollow nerve cord
A long supporting rod that
runs through the body just
below the nerve cord.
* Most chordates have this during their embryonic stage.
Notochord
These are paired structures in the
throat (pharynx) region.
* In some animals such as fishes
and amphibians these slits will
develop into gills, in higher
chordates it will disappear during
development.
Pharyngeal slits
Pharyngeal slits
adults that live in water and breathe via gills
Permanent slits
Pharyngeal slits
Adults live on land
temporary slits
Posteriorly located.
* contains bones and
muscles used by animals
for swimming and
balancing their body.
Tail
2 groups under phylum chordata
Group Protochordata (Acrania)
Group Craniata
Subphylum
Sea squirts and tunicates
Notochord, nerve cord, post-anal tail
present only in free-swimming larvae;
Ascidian adults sessile’ or occasionally
planktonic, encased in tunic that contain
some cellulose; marine
Subphylum Urochordata
Subphylum
Lancelets(Amphioxus) , Assymetron
Notochord, nerve cord, post-anal tail
and gill slits persist throughout life;
body laterally compresses and
transparent; fishlike form
Subphylum Cephalochordata
Gr. A- without, and gnathos – jaw
Cyclostoma: hagfishes and lampreys
Without true jaw and appendages
Superclass Agnatha
Fish-like; jawless; no paired
appendages; suctorial mouth with
horny teeth and rasping tongue;
nasal sac not connected to
mouth; seven pairs of gill slits
Class Cephalaspidomorphi
Fish-like; jawless; no paired
appendages terminal mouth with four
pairs of tentacles; no sac with duct to
pharynx; 5 to 15 pairs of slits; partially
hermaphroditic. Hagfishes
Class Myxini
Gr. Gnathos – jaw and stoma – mouth
Jawed fishes and all tetrapods
With jaws and usually paired appendages
Superclass Gnathostomata
Gr. Chondros - cartilage and ichthys
– fish
Streamed liked fish body with
heterocercal tail; cartilaginous
skeleton; five to seven gills with
separate openings; no operculum;
no swim bladder
Class Chondrichthyes
Gr. Osteon – bone and ichthys – fish
fusiform body; mostly ossified skeleton
single gill opening on each side covered with
operculum,; usually with swim bladder
Class Osteichthyes
