Introduction to Chordates BIO 122: Zoology Newberry College

Phylum Chordata 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: Notochord Dorsal tubular nerve cord Pharyngeal pouches and gill slits Endostyle 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 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 – 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 Expanded endoskeleton - living endoskeleton * internal skeleton, grows with the organism * commonly is hollow, provides support * distinctive covering around brain = cranium

Characteristics of Vertebrates 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 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 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 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 Lamprey (note gill slits)

CLASSIFICATION OF VERTEBRATES 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)