CHORDATA

CHORDATA

Derived from Greek word

chorde means string or cord ata means bearing
 Diversity of chordata

● 64832 species on record ● smallest - 10mm

● 32120 fishes [philippine gody]
● 6771 amphibians ● largest - 35 m
● 9320 reptiles Blue Whale]
● 9026 birds
● 5750 Mammals
 GENERAL CHARACTERISTICS

● Aquatic, terrestrial, aerial.

● All free living. no parasitic
● bilaterally symmetrical
● Presence of post anal tail
● Exoskeleton
● Triploblastic
● True coelom
● Cartilaginous or bony endoskeleton
● Pharyngeal gill slits at some stage of life, may/may
not be functional
● Complete digestive system
● Closed blood vascular system
● Excretory system - proto/meso/metanephric kidneys
● Dorsal and tubular nerve cord
● Sex are separate
 Fundamental Chordates Characteristics

● Dorsal hollow or tubular nerve cord

● Longitudinally supporting rod like notochord
● Pharyngeal gill slits
● Post-anal tail
 Dorsal hollow nerve cord

● Central nervous system is present dorsally

● Longitudinal hollow nerve tube present above the
notochord
 Notochord (Prime feature of chordates)

● Notochord is elongated
● Rod like
● Flexible
● Present beneath nerve cord
 Pharyngeal gill slits

● At some stage
● Paired lateral gill slits
● Pharyngeal wall of gut behind mouth
● Protochordates - present throughout life
● Higher vertebrates - disappear / modifies in adult
 CLASSIFICATION

On the basis of -

● Presence of notochord or vertebral column

● Presence or absence of Cranium

 Chordata

Groups Acrania Craniata

Subphylum Urochordata Cephalochordata

Vertebrata

Division Gnathostomata
Agnatha

Superclasses Pisces Tetrapoda

Classes Ostracodermi Cyclostomata

Classes Amphibia

Reptilia
Classes Chondrichthyes Osteichthyes
Aves

Mammalia
 GROUP A: Acrania (protochordata)

➔ All marine
➔ Primitive type
➔ Lacks head/skull/cranium
➔ Divided into two subphylum
◆ Urochordata
◆ Cephalochordata
 Subphylum I. Urochordata / Tunicata
➔ Notochord in larval stage only
➔ Adult appear sac like
➔ Sessile (not moving/fix at one position)
➔ Encased in protective tunic or test
➔ Divided into 3 classes
◆ Ascidiacea
◆ Thaliacea
◆ Larvacea/Appendicularia
➔ Class I: Ascidiae

◆ Sessile
◆ Scattered muscles in tunic
◆ Solitary / colonial / compound
◆ Gill clefts numerous

Herdma nia
 Class II: Thaliacea

➔ Free swimming
➔ Circular muscles in tunic

Scalpa
CLass III: Larvacea [Thaliacea]
/ Appendicularia

➔ Tiny, Transparent
➔ Free floating

Oikopleura
[Larvaceae]
 Subphylum II. Cephalochordata
➔ Notochord and nerve cord present
throughout life along entire length body

➔ Class Leptocardii
◆ Body fish like
◆ Segmented with distinct myotomes
and numerous gill-slits Asymmetron
(Lancelet)
◆ Have one family, 2 genera and 30
species
 Group B: Craniata /Euchordata

➔ Aquatic, terrestrial, aerial

➔ With distinct head
➔ Vertebral column
➔ Jaws present
➔ Brain protected by skull or cranium
 Subphylum III. Vertebrata

➔ Notochord replaced by vertebral column

➔ Body divisible into head,neck, trunk and tail
➔ Largest subphylum with 46500 species

➔ Two Divisions
◆ Agnatha
◆ Gnathostomata
 DIVISION I: Agnatha
➔ Jawless primitive fish
➔ Without true jaws
➔ Paired fins were absent
(median and caudal fin
present) Cephalapsis
➔ Have 2 classes

➔ Class I: Ostracodermi
◆ The extinct order
◆ Primitive heavily armoured
◆ The first vertebrate
 ➔ Class II: Cyclostomata

◆ Eel shaped
◆ Without scales, jaws and lateral fins
◆ Mouth round and suctorial

Myxine

Petromyzon mouth
 DIVISION II:
Gnathostomata
➔ True jaws
➔ Paired fins/limbs
➔ Have twosuperclasses

◆ Pisces
◆ Tetrapoda
Superclass I: Pisces

➔ Scaly skin
➔ Gills
➔ Paired fins
➔ Have 3 classes
Climatius
➔ Class I: Placodermi (Extinct)
◆ Primitive
◆ Jawed fishes
◆ Bony heads
➔ Class II: Chondrichthyes

◆ Cartilaginous endoskeleton
◆ Placoid scales
◆ Gill slits not covered with
operculum
◆ Pelvic claspers in males

Selachimorpha (Shark)
 ➔ Class III:Osteichthyes
◆ Bony endoskeleton
◆ cycloid/ ctenoid scales
◆ Gill slits covered with operculum
◆ Males without claspers

Hippocampus
Superclass II: Tetrapoda

➔ Land vertebrate
➔ Two pairs of pentadactyle limbs
➔ Cornified skin and lungs
➔ Have 4 classes
➔ Class I:Amphibia

◆ Aquatic larval stage

◆ Larva have gills
◆ Adults terrestrial
◆ Adults breathe through
lungs
◆ Moist skin
◆ 3 chambered heart Ambystoma
[salamander]
 ➔ Class II: Reptilia
◆ Terrestrial
◆ Dry skin
◆ Horny scales
◆ Heart incomplete 4 chambered
◆ Cold blooded
◆ Respiration by lungs
Crocodylinea
 ➔ Class III: Aves

◆ Flying vertebrate
◆ Covered with feathers
◆ Forelimbs modified into
wings
◆ No teeth in beak
◆ 4 chambered heart
◆ Warm blooded

Pavo cristatus
 ➔ Class IV:Mammalia

◆ Body covered with hair

◆ Glandular skin
◆ Female with mammary
glands
◆ 4 chambered heart
◆ Warm blooded
Panthera leo
Protochordata
 Proptochordata= First chordates

Urochordata Cephalochordata
 General Characters of Protochordata
1. Exclusively marine and small forms.
2. Cranium or brain-box, jaws, vertebral column and pair appendages are absent.
3. Dorsal tubular nerve cord, notochord, gill-slits and myotomes are usually
present.
4. Sexes may be separate or united.
5. This group includes the lowly-organised members of Phylum Chordata.

SUBPHYLUM II- Urochrodata (tunicata)

1. Exclusively marine commonly known as sea squirts.

2. Solitary or colonial.
3. Fixed or free-swimming.
4. Body is covered by a cuticular tunic or test in adult stage. [Tunicine (C6H10O5)n]
5. Notochord present in the larval stages and absent in the adults.
6. Dorsal tubular nerve cord is present in the larval forms, while degenerates in the form
of small ganglion in adults.
7. Numerous pharyngeal gill-slits are present.
8. Heart is ventral, simple and tubular.
9. Sexes are united, i.e., hermaphrodite.
Class I-ASCIDIACEA
1. Solitary, colonial or compound. Bottom living.
2. Body form and size variable.
3. Test permanent, well developed and thick.
4. Atrium opens dorsally by atriopore.
5. Pharynx large with many persistent gill-slits.
6. Sexes united. Larva free-swimming and highly developed
7. Adults usually sessile after retrogressive metamorphosis when larval notochord, nerve
cord and tail are lost and brain reduced to a solid dorsal ganglion.
8. Stolon simple or none.
Order 1. Enterogona
1. Body sometimes divided into thorax and
abdomen.
2. Neural gland usually ventral to ganglion.
3. Gonad, lying in or behind intestinal loop.
4. Larva with 2 sense organs (ocelli and
otolith).
Examples: Ciona, Phallusia.

Order 2. Pleurogona
1. Body compact, undivided.
2. Neural gland dorsal or lateral to ganglion.
3. Gonads 2 or more embedded in mantle
wall. Ciona
4. Larva with otolith.
Examples: Herdmania, Botryllus, Molgula,
Styela.

Botryllus
Herdmania
Class II-THALIACEACA

1. Adults free living, pelagic, in warm and temperate seas. Solitary or

colonial.
2. Body shape and size variable
3. Tunic permanent, thin and transparent, with circular muscle bands.
4. Atriopore located posteriorly.
5. Pharynx with 2 large or many small gill-slits.
6. Sexes united. Larva formed or absent.
7. Adult without notochord, nerve cord and tail.
8. Asexual budding/reproduction from complex stolon.
9. Life history with an alternation of generations.

Order I. Pyrosomida

1. Colony compact, tubular, closed at one and phosphorescent

throughout the life, to the invasion of its egg by a symbiluminescent
bacteria.
2. Zooids embedded in a common test.
3. Muscle bands confined to body ends.
4. Gill-slits tall, numerous, upto 50.
5. No free-swimming larval stage.
6. Reproduces by budding.
Examples : Single genus, Pyrosoma.
Order 2. Doliolida (=Cyclomyaria)
1. Body characteristically barrel-shaped.
2. Muscle bands form 8 complete rings.
3. Gill-slits small, few to many.
4. A tailed larva with notochord present.
Examples : Doliolum, Doliopsis.

Order 3. Salpida (= Desmomyaria)

1. Body cylindrical or prism-shaped.
2. Muscle bands incomplete ventrally.
3. Pharynx communicates freely with atrium through a large gill-slit.
4. Tailed larva absent.
Examples : Salpa, Scyclosalpa.
 Class III: LARVACEA

1. Small (5 mm long), solitary, free-swimming, pelagic, neotenic,

larva-like forms with persistent tail, notochord, nerve cord and
brain.
2. Test forming a temporary house, renewed periodically
3. Atrium and atrial aperture absent.
4. Gill-slits 2, opening directly to outside.
5. Sexes united. No metamorphosis.
Examples: 1. Oikopleura, 2. Appendicularia.

Order 1: Endostylophora
1. House bilaterally symmetrical, with separate inhalent and Appendicularia
exhalent apertures.
2. Pharynx with endostyle.
Examples : Oikopleura, Appendicularia

Order 2:. Polystylophora

1. House biradially symmetrical, aperture with single aperture
2. Pharynx without endostyle.
Example: Kowalevskia.
 Herdmania

Ciona Ascidia
Phylum: Chordata
Group: Protochordata
Subphylum: Urochordata
Class: Ascidiacea
Order: Ascidiae simplices
Genus: Herdmania
Species: pallida

Habit and Habitat. Henimania pallida is a solitary, sedentary marine form. They sometime
live as commensalism with gastropod shells like Xanchus species (Shankh and Conch).

1. Herdmania is commonly called sea squirt.

2. Animal is attached at its postero-ventral end by a foot, which is large, rough, leathery
with attached foreign objects.
3. Body is roughly oblong in outline, about 9.5 to 12 cm long and 5.2 to 6.9 cm in
breadth, and enclosed in a soft leathery test or tunic formed of tunicin and protein.
4. The colour of the body of a fresh specimen is pink.
5. Free end (antero-dorsal) of the body is provided with branchial and the atrial apertures
located over branchial and atrial siphons respectively,
6. Mouth opens by branchial aperture, while anus by atrial aperture.
7. Pharynx is sac-like perforated by numerous stigmata.
8. Alimentary canal is U-shaped. Food comprises chiefly microscopic plants and animals,
viz. diatoms, algae and infusorians.
9. Respiration by branchial-sac, Test also acts as an accessory respiratory organ.
10. Blood vascular system is open type.
11. Excretory organ is neural gland situated above the nerve ganglion.
12. Sexes are united or hermaphroditic and protogynous. Gonads only a single pair.
13. Fertilization is external. Development includes a free-swimming tadpole larva
having all the chordate characters (dorsal nerve cord, and notochord).
14. Metamorphosis is retrogressive in which nerve cord, notochord, tail with tail fins
degenerate. it looses chordate characters.

Geographical distribution. Herdmania pallida is found in Indian, Pacific and the

Atlantic Oceans and also from Malya and West Indies.
SUBPHYLUM I-CEPHALOCHORDATA

1. Exclusively marine and solitary forms.

2. Notochord and nerve cord extend the entire length of the body.
3. Notochord persists as such.
4. Limbs or paired fins are absent. Median fins are present.
5. Mouth is ventral and anterior, while anus is ventral and posterior.
6. Pharynx is large, perforated by numerous pharyngeal gill-slits and surrounded by
atrium.
7. Exoskeleton, head, brain, auditory organs, and jaws are absent.
8. Sexes are separate.
9. Gonads are metamerically arranged on the body wall.

Example: Amphioxus (= Branchiostoma)

Phylum: Chordata
Group: Protochordata
Subphylum: Cephalochordata
Class: Leptocardiion
Genus: Amphioxus (Branchiostoma)
Species: lanceolatum

Habit and Habitat. Amphioxus is a fish-like burrowing marine animal. It burrows in the
sand by its posterior end, anterior end protrudes out of the sand for feeding. It is a ciliary
feeder.
1. Amphioxus is commonly called lancelet.
2. Body is elongated, measuring 5 cm in length, laterally compressed and pointed at both
ends. The anterior end projects forwards as the rostrum.
3. The fins are low and continuous with each other, a dorsal, a ventral and a caudal fin.
There are two metapleural folds, extending up to atriopore.
4. The myotomes are arranged on both the sides separated by V-shaped connective
tissue partitions, the myosepta or myocommata.
5. The atriopore is median and ventral and lies at the junction of metapleural folds and
ventral fin.
6. Alimentary canal is straight. The mouth is ventral to rostrum and is guarded by the oral
hood bearing numerous oral cirri. The anus lies on the left side, a short distance in
front of the posterior end.
7. Notochord extends throughout the length of the body and nerve cord lies above
the notochord whose anterior end is swollen forming the unspecialised brain.
8. The gonads consist of 26 pairs and are metamerically arranged on both the sides of
the pharynx, beneath the myotomes.
9. The sexes are separate but externally not distinguishable (absence of sexual
dimorphism).

• Geographical distribution. Amphioxus lanceolatum is worldwide in distribution

being found on the shores of all continents and many oceanic islands.

• Special features: Amphioxus shows primitive, specialized and degenerate

characters.

• Primitive characters are notochord extending into snout, segmented myotomes,

absence of paired fins and jaws, straight intestine, ciliary feeding and tubular heart.

• Specialised characters are eleborated oral hood and velum and several pharyngeal
gill-slits.
• Degenerate features are unspecialised, reduced brain and sense organs.