Introduction to
Chordates
BIO 122: Zoology
Newberry College
Phylum Chordata
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Most complex of all phyla
All have a notochord
rod-like semirigid body of cells
usually extends length of body
ventral to nervous system’s spine
Purposes:
1) support & stiffen body
2) provide skeletal support for muscles
Phylum Chordata
Five important features of chordates:
1. Notochord
2. Dorsal tubular nerve cord
3. Pharyngeal pouches and gill slits
4. Endostyle
5. Postanal tail
Chordate characteristics
1) Notochord - a flexible, rod-like structure
* beginning of the internal skeleton
* axis for muscle attachment, flexible w/o
shortening
* in vertebrates the notochord becomes
segmented as vertebrae
Chordate characteristics
2) Dorsal Tubular Nerve Cord - produced by
infolding of ectoderm during early development
* in many invertebrates the nerve cord is
ventral and solid
* in many anterior end becomes swollen = brain
Chordate characteristics
3) Pharyngeal Pouches and Gill Slits perforated openings
* lead from pharyngeal cavity to outside body
* in simplest aquatic chordates it allows for
suspension feeding
* in terrestrial organisms is only developmental
Chordate characteristics
4) Endostyle - or its derivative, the thyroid gland
* in the simplest chordates the endostyle
secretes mucus that traps small food particles
Chordate characteristics
5) Postanal Tail - extension of body beyond anus
* enhances ability for movement (aquatic) &
balance (terrestrial)
Additional Chordate Features
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Development pattern as in Echinoderms:
radial, indeterminate cleavage
deuterostome
enterocoelous
Segmented muscles in an unsegmented body
Complete digestive system
Closed circulatory system
Endoskeleton made of cartilage and/or bone
Classification of Chordates
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Three distinct Subphyla:
Urochordata – tunicates
Cephalochordata – lancelets
Vertebrata - vertebrates
Subphyla of Chordates
SUBPHYLUM UROCHORDATA - tunicates
 Only larval form moves, adults are sessile
larvae with all chordate characteristics
 Adults relatively small, up to a few cm long
* produce a leathery outer surface (= tunic)
* loss of notochord & tail, nerve cord greatly reduced
* become filter feeders with siphons
* gills slits become net-like to trap food
 Individuals are hermaphroditic
* reproductive cells into water, external fertilization
Diagramatic tunicate
Subphyla of Chordates
SUBPHYLUM CEPHALOCHORDATA - lancelets
 Slender, lancet-shaped, 5-7 cm long
* sandy bottoms of shallow marine environments
 Adults clearly with all the chordate characteristics
* suspension feeders, trap food in gills slits
* circulatory system closed, but no distinct heart
* no obvious brain
 Separate males and females
* fertilization external
Diagramatic lancelet
Subphyla of Chordates
SUBPHYLUM VERTEBRATA - vertebrates
 Very large and diverse group
well known due to large size
 Not all chordate
features in adults
Characteristics of Vertebrates
1.
Expanded endoskeleton - living endoskeleton
* internal skeleton, grows with the organism
* commonly is hollow, provides support
* distinctive covering around brain = cranium
Characteristics of Vertebrates
2.
Gills in pharynx - better respiration
* other subphyla use slits for filter feeding
* more active aquatic vertebrates developed
gills with muscles
* heart developed to enhance circulation
Characteristics of Vertebrates
3.
Enhanced Nervous System –
* with anterior swelling
* more complex behaviors of swimmers &
predators
* has tripartite brain (fore-, mid- and hind-brain)
* development of enhanced senses
Characteristics of Vertebrates
4.
Development of neural crest & ectodermal
placode – enhances complexity
* neural crest
enhances development of skeleton,
tooth dentine & endocrine glands
* ectodermal placodes enhance
sensory development (olfactory, eye, ear)
CLASSIFICATION OF
VERTEBRATES
Several important characteristics to separate:
1) skeleton & jaw composition: cartilage or bony
2) number & structure of paired appendages
3) dermal covering over body
4) relative number of gill slits of an adult
5) type of covering over egg
CLASSIFICATION OF
VERTEBRATES
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SUPERCLASS AGNATHA
lampreys & hagfish
cartilaginous skeleton and no jaw
no paired appendages
skin smooth (slimy)
about 7 gill slits per side
eggs with gelatinous covering (aquatic)
heart 2-chambered (1 atrium + 1 ventricle)
SUPERCLASS AGNATHA
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Lamprey (note gill slits)
CLASSIFICATION OF
VERTEBRATES
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SUPERCLASS GNATHOSTOMATA
All other vertebrates with jaws & paired
appendages
CLASSIFICATION OF
VERTEBRATES
Class Chondrichthyes (sharks & rays)
 cartilaginous skeleton and jaw present
 2 pair fins
 placoid scales
(tooth like with root)
 5-7 pair gill slits
 eggs with gelatinous
covering (aquatic)
CLASSIFICATION OF
VERTEBRATES
Class Actinopterygii (bony ray-finned fish)
 bony skeleton, jaw present
 2 paired appendages; fins
 overlapping dermal scales
(typically thin & flexible)
 gill slits with covering
operculum
 egg covering gelatinous
CLASSIFICATION OF
VERTEBRATES
Class Amphibia (amphibians)
 bony skeleton, jaw present
 2 paired appendages, legs
 smooth skin
 gills only in juvenile forms
 eggs with gelatinous covering (aquatic)
CLASSIFICATION OF
VERTEBRATES
Class Reptilia (reptiles)
 bony skeleton, jaw present
 2 paired appendages, legs
 hard scales (snakes) or plates (turtles)
 gills embryonic only
 eggs with leathery
covering (terrestrial)
CLASSIFICATION OF
VERTEBRATES
Class Aves (birds)
 bony skeleton, jaw present
 2 paired appendages;
legs + wings
 feathers + scales on legs
 gills embryonic only
 eggs with calcified shell
(terrestrial)
CLASSIFICATION OF
VERTEBRATES
Class Mammalia (mammals)
 bony skeleton, jaw present
 2 paired appendages; legs (+ arms)
 fur and/or hair
 gills embryonic only
 viviparous (few with calcified shells)