Phylum chordata :
» Phylum chordata was created by Balfour in 1880.
» Originated prior to cambrian period.
» Fundamental chordate characters are notochord, dorsal tubular nerve cord, gillslits & post and tail
» Notochord originates from mesoderm.
» Present below the nervecord and above the alimentary caual as a middorsal solid rod like structure.
» Covered by outer elastic sheath, inner fibrous sheath and filled by vacuolated cells.
» Persistent throughout life in cephalochordata, cyclostomes and some fishes.
» Replaced by vertebral column in vertebrates during development.
» Nuclei pulposi are remains of notochord present at the centre of inter vertebral discs in mammals.
» Dorsal tubular nerve cord originates from ectoderm
» Present above the notochord and out side the coelom
» Forms into anterior brain and continues as spinal cord in vertebrates Gill slits-originate both from ectoderm and endoderm
» Paired lateral openings of pharynx through which water is sent outside.
» Formed by the outpushings of endodermal lining of pharynx and inpushings of ectoderm from exterior with the intervening walls broken during development
» Persistant in protochordates, cyclosto mes fishes and some aquatic amphi bians throughout life.
» vascular and act as gills for respiration in fishes, aquatic urodeles and amphibian larvae.
» useful mainly for filter-feeding in protochordates.
» Postanal tail -is the posterior part of body behind anus or cloaca.
» without coelom and viscera
» notochord, nervecord & muscles are extending into the tail.
Other chordate characters are :
» Ventral muscular myogenic heart
» Hepatic portal system
» Deuterostomous nature
» Radial and indeterminate cleavage
» Enterocoelomates but higher chordates are secondarily schizocoelomate in nature.
» Presence of creatine phosphate as muscle phosphagen
» Comparasion of chordates & nonchordates : Chordates Non chordates
1 Notochord present Notochord absent
2 Dorsal, tubular, ventral, solid, double single, nonganglionated nerve cord ganglionated nervecord
3 Ventral heart Dorsal heart
4 Blood flow is anterior to posterior in Blood flows from posterior to anterior in dorsal. dorsal blood vessels and posterior to vesselsand anterior to posterior in ventral vessels. anterior in ventral blood vessels
5 Muscle phosphagen is creatine Muscle phosphagen is arginine phosphate or both
» phosphate argininephosphate and creatine phosphate
6 Haemoglobin is present in blood Respiratory pigment dissolved-in plasma corpuscles
7 Gill slits present Gill slits absent
Classification of phylum chordata Sub phylum I : Urochordata/ Tunicata
Marine
» Sedentary or free swimming
» Solitary or colonial
» Body covered by test made of tunicin
» Notochord and nervecord present in larval stages and absent in adults
» Numerous gill slits
» Filter feeders
» Endostyle helps in feeding
» Heart tubular, functions alternately as branchial and systemic heart
» Open circulation
» Hermaphrodite, development indirect
Divided into 3 classses:
Class i)Ascidiacea -
Eg. Herdmania Ascidia Botryllus Ciona
Class ii)Thaliacea -
Eg. Salpa Doliolum Pyrosoma
Class iii)Larvacea/Appendicularia-
Eg. Oikopleura
Subphylum-II: Cephalochordata
» Marine, solitary, burrowing forms
» Typical chordates
» Notochord extends from anterior end to posterior end
» Paired fins absent
» Filter feeders with numerous pharyngeal gill slits
» Endostyle present
» Closed circulation but heart, respiratory pigment & blood corpuscles absent.
» Excretion by protonephridia with solenocytes
» Unisexual,gonoducts absent
» Development indirect
Eg. Branchiostoma(=Amphioxus), Asymmetron
Subphylum III: Vertebrata (or craniata)
» Chordates with vertebral column
» Vertebrae surround the dorsal nerve cord
» Divided into superclasses Agnatha and Gnathostomata, basing on presence and absence of jaws.
Superclass Agnatha:
» Jaw less vertebrates
» Paired appendages absent
» Single nostril
Class1: Ostracodermi-extinct agnathan group
» Ancestors of fishes
Eg. Cephalaspis, Hemicyclaspis
Class 2: Cyclostomata - extant group
» Includes lampreys, myxines
» Exoskeleton absent
» Body elongated eel like with circular suctorial mouth
» Paired fins absent
» 6-14 pairs of gill pouches
» Notochord persistent
» Cartilaginous endoskeleton
» 2 -chambered heart and mesonephric kidneys
» Single gonad and gonoducts absent
» Development indirect with ammocoete larva in lampreys
» Direct development in hag fish.
Eg: Petromyzon(Lamprey) -ectoparasitic, sanguivore
» exhibits anadromous migration during breeding season Myxine (Hag fish or slime eel)- necrophagous Super class-II: Gnathostomata- Jawed vertebrates
» Paired fins or limbs present
» Paired nostrils present Internal ear with 3 semicircular canals
» Includes pisces and tetrapods
» Pisces and amphibians are called Ichthyopsida
» Reptiles and aves are called Saurop sida
» Pisces, amphibians and reptiles are poikilotherms
» Aves and mammals are homeotherms
» Pisces and amphibians are anamniotes
» Reptiles, aves and mammals are amniotes
PISCES
» Most diverse and the largest group of vertebrates
» Study of fishes is called Ichthyology
» Originated during silurian period
» Devonian period is age of fishes
» Ostracoderms are the ancestors of fishes
» Acanthodians are the earliest group of fishes which gave rise to osteichthyes (bony fishes)
» Placoderms gave rise to chondrichthyes (cartilaginous fishes)
» Body is streamlined and differentiated into head, trunk and tail
» Body covered by mesodermal scales
» Skull monocondylic
» Vertebrae amphicoelous
» Locomotion by unpaired and paired fins
» Teeth homodont, acrodont and polyphyodont
» Respiration by gills
» Heart 2-chambered and described venous heart and branchial heart
» Single circuit circulation
» Kidneys mesonephros
» Brain covered by single meninx called meninx primitiva
» Cranial nerves 10 pairs
» Lateral line sense organs/Neuromast organs present for rheoreception. Pisces include 2 extant classes
Class i) Chondrichthyes-
» Marine fishes with cartilagenous endoskeleton
» Body covered by placoid scales
» Caudal fin heterocercal
» Mouth ventral
» Gills lamelliform and without operculum
» Air bladder absent
» Ureotelic animals and many exhibit physiological uraemia (an adaptation to live in hypertonic medium)
» Pelvic fins bear claspers, acting as copulatory organs
» Fertilisation internal
» Many are viviparous
Eg: Scoliodon (Dog fish) Scyllium (Shark) Rhinodon (Whale shark) Carcharadon (Great white shark) Sphyrna (Hammer headed shark)
