introduction to chordates bio 122: zoology newberry college

Introduction to Chordates

BIO 122: ZoologyNewberry College

Phylum Chordata

Most complex of all phyla All have a notochord

rod-like semirigid body of cellsusually extends length of bodyventral to nervous system’s spine

Purposes:1) support & stiffen body2) provide skeletal support for muscles

Phylum Chordata

Five important features of chordates:1. Notochord2. Dorsal tubular nerve cord3. Pharyngeal pouches and gill slits4. Endostyle5. 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


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


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


4) Endostyle - or its derivative, the thyroid gland* in the simplest chordates the endostyle secretes mucus that traps small food particles


5) Postanal Tail - extension of body beyond anus* enhances ability for movement (aquatic) & balance (terrestrial)

Additional Chordate Features

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

Three distinct Subphyla:Urochordata – tunicatesCephalochordata – lanceletsVertebrata - 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


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 lanceletDiagramatic lancelet


SUBPHYLUM VERTEBRATA - vertebrates

Very large and diverse groupwell known due to large size

Not all chordatefeatures 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


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


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


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 bony2) number & structure of paired appendages3) dermal covering over body4) relative number of gill slits of an adult5) type of covering over egg


SUPERCLASS AGNATHA lampreys & hagfishcartilaginous skeleton and no jawno paired appendagesskin smooth (slimy)about 7 gill slits per sideeggs with gelatinous covering (aquatic)heart 2-chambered (1 atrium + 1 ventricle)

SUPERCLASS AGNATHA

Lamprey (note gill slits)


SUPERCLASS GNATHOSTOMATA All other vertebrates with jaws & paired appendages


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)


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


Class Amphibia (amphibians) bony skeleton, jaw present 2 paired appendages, legs smooth skin gills only in juvenile forms eggs with gelatinous covering

(aquatic)


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))


Class Aves (birds) bony skeleton, jaw present 2 paired appendages;

legs + wings feathers + scales on legs gills embryonic only eggs with calcified shell

(terrestrial)


Class Mammalia (mammals) bony skeleton, jaw present 2 paired appendages; legs (+ arms) fur and/or hair gills embryonic only viviparous (few with calcified shells)

introduction to chordates bio 122: zoology newberry college

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