Chordata is the largest phylum with most familiar group of animals, such as fishes, amphibians, reptiles, birds and mammals and less known forms such as lancelets (Amphioxus) and tunicates (Ascidian). All chordates possess three fundamental distinct features at some stage of their life cycle (Figure 2.19), they are:
Figure 2.19
1. Presence of elongated rod like notochord below the nerve cord and above the alimentary canal. It serves as a primitive internal skeleton. It may persist throughout life in lancelets and lampreys. In adult vertebrates, it may be partially or completely replaced by backbone or vertebral column.
2. A dorsal hollow or tubular fluid filled nerve cord lies above the notochord and below the dorsal body wall. It serves to integrate and co-ordinate the body functions. In higher chordates, the anterior end of the nerve cord gets enlarged to form the brain and the posterior part becomes the spinal cord, protected inside the vertebral column.
3. Presence of pharyngeal gill slits or clefts in all chordates at some stage of their lifecycle. It is a series of gill slits or clefts that perforates the walls of pharynx and appears during the development of every
Table.1
Figure 2.31
comarision of chrdates and non-chordates
chordate. In aquatic forms, pharyngeal gill slits are vascular, lamellar and form the gills for respiration. In terrestrial chordates, traces of non-functional gill clefts appear during embryonic developmental stages and disappear later. Besides the above said features, chordates are bilaterally symmetrical, triploblastic, coelomates with organ system level of organisation; they possess post anal tail, closed circulatory system with a ventral myogenic heart except in Amphioxus.
List the three features common to all chordates at sometime in their life.
(G. Oura – A tail; L. Chord – cord) They are exclusively marine and are
commonly called sea squirts. Mostly sessile, some pelagic or free swimming, exist as solitary and colonial forms. Body is
Figure 2.20
unsegmented and covered by a test or tunic. Adult forms are sac like. Coelom is absent, but has an atrial cavity surrounding the pharynx. Notochord is present only in the tail region of the larval stage, hence named urochordata. Alimentary canal is complete and circulatory system is of open type. The heart is ventral and tubular. Respiration is through gill slits and clefts. Dorsal tubular nerve cord is present only in the larval stage and a single dorsal ganglion is present in the adults. Mostly hermaphrodites, development indirect and includes a free swimming tadpole larva with chordate characters. Retrogressive metamorphosis is seen (Figure 2.20).
( L*. Cephalo-* ‘head’ ; G. chorda ‘cord’.) Cephalochordates are marine forms,
found in shallow waters, leading a burrowing mode of life. They are small fish like coelomate forms with chordate characters such us notochord, dorsal tubular nerve cord and pharyngeal gill slits throughout their life. Closed type of circulatory system is seen without heart. Excretion is by protonephridia. Sexes are separate, Fertilization is external. Development is indirect and includes a free swimming larva (Figure 2.21).
Vertebrates are also called higher chordates and they possess notochord during embryonic stage only. The notochord is replaced by a cartilaginous or bony vertebral column in the adult. Hence all vertebrates are chordates but all chordates are not vertebrates. Vertebrates possess paired appendages such as fins or limbs. Skin is covered by protective skeleton comprising of scales, feathers, hairs, claws, nails, etc. Respiration is aerobic through gills, skin, buccopharyngeal cavity and lungs. Vertebrates have a ventral muscular heart with two, three or four chambers and kidneys for excretion and osmoregulation.
Subphylum Vertebrata is divided into two divisions, Agnatha and Gnathostomata. Agnatha includes jawless fish-like aquatic vertebrates
without paired appendages. Notochord persists in the adult. Gnathostomata includes jawed vertebrates with paired appendages. Notochord is replaced partly or wholly by the vertebral column. Agnatha includes one important class – Cyclostomata. Gnathostomata includes jawed fishes (Pisces) and Tetrapoda ( amphibia, reptilia, aves and mammals). The superclass Pisces includes all fishes which are essentially aquatic forms with paired fins for swimming and gills for respiration. Pisces includes cartilaginous fishes (Chondrichthyes) and bony fishes (Osteichthyes).
All members of cyclostomata are primitive, poikilothermic, jawless aquatic vertebrates and are ectoparasites on some fishes. Body is slender and eel-like bearing six to fifteen pair of gill slits for respiration.Mouth is circular without jaws and suctorial. Heart is two chambered and circulation is of closed type. No paired appendages. Cranium and vertebral column are cartilaginous. Cyclostomes are marine but migrate to fresh waters for spawning (anadromous migration). After spawning within a few days they die. The larvae (ammocoete) after metamorphosis returns to the ocean. Examples: Petromyzon (Lamprey) and Myxine (Hag fish) (Figure 2.22).
(G. chondros –cartilage; ichthys -fish) They are marine fishes with cartilaginous
endoskeleton. Notochord is persistent throughout life. Skin is tough covered by dermal placoid scales and the caudal fin is heterocercal (asymmetrical both externally and internally). Mouth is located ventrally and teeth are modified placoid scales which are backwardly directed. Their jaws are very powerful and are predaceous animals. Respiration by lamelliform gills without operculum (gill cover). Excretory organs are mesonephric kidneys. Two chambered heart is present. Cartilaginous fishes are ureotelic and store urea in their blood to maintain osmotic concentration of body fluids. They are poikilothermic and viviparous. Sexes are separate. In males pelvic fins bear claspers to aid in internal fertilisation.
It includes both marine and freshwater fishes with bony endoskeleton and spindle
Figure 2.23
shaped body. Skin is covered by ganoid, cycloid or ctenoid scales. Respiration is by four pairs of filamentous gills and is covered by an operculum on either side. Air bladder is present with or without a connection to the gut. It helps in gaseous exchange (lung fishes) and for maintaining buoyancy in most of the ray finned fishes. They have a ventrally placed two chambered heart. Excretory organs are mesonephrickidneys and are ammonotelic. Presence of well developed lateral line sense organ. Sexes are separate, external fertilization is seen and most forms are oviparous (Figure 2.24).
Amphibians are the first vertebrates and tetrapods to live both in aquatic as well as terrestrial habitats.They are poikilothermic. Their body is divisible into the head and trunk and most of them have two pairs of limbs; tail may or may not be present. Their
skin is smooth or rough, moist, pigmented and glandular. Eyes have eyelids and the tympanum represents the ear. Respiration is by gills, lungs and through the skin. Heart is three chambered. Kidneys are mesonephric. Sexes are separate and fertilization is external. They are oviparous and development is indirect. They show hibernation and aestivation.
They are mostly terrestrial animals and their body is covered by dry, and cornified skin with epidermal scales or
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scutes. Reptiles have three chambered heart but four chambered in crocodiles. All are cold blooded amniotes (poikilotherms). Most reptiles lay cleidoic eggs with extraembryonic membranes like amnion, allantois, chorion and yolk sac. Excretion by metanephric kidneys and are uricotelic. Sexes are separate with well marked sexual dimorphism. Internal fertilization takes place and all are oviparous.
(L. Avis –bird) Aves are commonly known as birds.The characteristic feature of Aves is the presence of feathers and the ability to fly except for flightless birds (Eg. Ostrich, Kiwi, Penguin). The forelimbs are modified into wings, and the hind limbs are adapted for walking, running, swimming and perching. The skin is dry and devoid of glands except the oil gland or preen gland at the base of the tail. The exoskeleton consists of epidermal feathers, scales, claws on legs and the horny covering on the beak. The endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities (pneumatic bones). The pectoral muscles of flight (pectoralis major and pectoralis minor) are well developed. Respiration is by compact, elastic, spongy lungs that are continuous with air sacs to supplement respiration. The heart is four chambered. Aves are homeothermic. Migration and parental care is well marked. Urinary bladder is absent. Sexes are separate with well marked sexual dimorphism. In males, the testes are paired but in females, only the left ovary is well developed while the right ovary is atrophied. All birds are oviparous. Eggs are megalecithal and cleidoic. Fertilization is internal.
Hooded Pitohui
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(Pitohui dichrous) The Hooded Pitohui is a songbird found in the rain forests of New Guinea, The first poisonous bird to be documented A neurotoxin called Homobatrachotoxin is found in its skin and feathers, causes numbness and tingling in those touching the bird.
They are found in a variety of habitats. Their body is covered by hair, a unique feature of mammals. Some of them are adapted to fly or live in water. Presence of mammary glands is the most unique feature of mammals. They have two pairs of limbs adapted for walking, running, climbing, burrowing, swimming and flying. Their skin is glandular in nature, consisting of sweat glands, scent glands and sebaceous glands. Exoskeleton includes horny epidermal horns, spines, scales, claws, nails, hooves and bony dermal plates. Teeth are thecodont, heterodont and diphyodont. External ears or pinnae are present. The heart is four chambered and possess a left systematic arch. Mature RBCs are circular, biconcave and non nucleated. Mammals have a large brain when compared to other animals They show greatest intelligence among all animals. Their kidneys are
metanephric and are ureotelic. All are homeothermic, sexes are separate and fertilization is internal.
Summary
Kingdom Animalia comprises of a broad range of animal species, from tiny parasitic nematodes to the largest mammal the blue whale. The basic fundamental features such as levels of organisation, diploblastic and triploblastic organisation, patterns of symmetry, coelom, segmentation and notochord have enabled us to broadly classify the animal kingdom. Besides the fundamental features, there are many other distinctive characters which are specific for each phyla or class.
Animals are broadly classified into invertebrates and chordates. The animals which lack vertebral column are called invertebrates. The chordates are characterized by the presence of notochord, solid ventral nerve cord and gill slits. Kingdom Animalia are classified into eleven animal phyla as Porifera, Cnidaria, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata and Chordata. Chordata is the largest phylum with three sup phyla Urochordata, Cephalochordata and Vertebrata. Subphylum Vertebrata includes two divisions, Agnatha and Gnathostomata. Agnatha comprises of the class Cyclostomata. Gnathostomata includes jawed fishes (Pisces) and Tetrapoda which includes the classes amphibia, reptilia, aves and mammals.
Sálim Moizuddin
Abdul Ali
Figure 2.30
is the leadi Indian Ornithology and generally referred as India". He was born on 12 November 1896 in he was the most respected and influential na century in India, He passed away on 20 June Salim got interested in birds when he was ten. Later he has conducted many systemati across India and the neighboring countries many bird books and popularized ornitho ‘Book of Indian birds’ and the ‘Hand boo India and Pakistan’ are the most important written. His autobiography ‘Fall of a spar the beginning and experience of his life wi him with the award of Padma Bhusahan in nominated to Rajyasabha in 1985. Salim Al of people to the field of ornithology and natu in India trace back their initial motivation t
In 1990, Government of India started honour called Sálim Ali Centre for Ornith Coimbatore, Tamil Nadu. SACON is a Ce by the Ministry of Environment, Forest an All the researches and activities of SACON of India’s Biodiversity with focus on birds. in the sylvan surrounding of Anaikatty, city, within the Nilgiri Biosphere Reserve India’s biodiversity and its sustainable use participation with birds at the centre stage. S covering all aspects of biodiversity and natu have completed PhD in Ornithology and Na of existence. SACON is known for its man and international journals. Nature Educatio in the region which is inculcating love for especially to school children every year. and Salim Ali Trophy Nature Competitions Forum of SACON is the people’s bird watc by SACON.
ng pioneer of “Bird Man of Bombay and turalist of 20th 1987. Young at the age of c bird surveys . He authored logy in India. k of Birds of books he has row’ narrates th birds. Government of India honoured 1958 and Padma Vibhushan 1976. He was i through his books motivated thousands ral history. Most of the environmentalists o bird watching and Salim Ali’s books. a national research institution in his ology and Natural History (SACON) in
ntre of excellence in research supported d Climate Change, Government of India. is devoted to the cause of conservation The main campus of SACON is situated 24 kilometers northwest of Coimbatore . SACON’s mission is to help conserve through research, education and people’s ACON conducts research in Ornithology
ral history. More than 50 research scholars tural history from SACON in its 25 years y research papers published in national n programme of SACON is very popular birds and nature to thousands of people Children’s Ecology Congress of SACON are flagship events. Salim Ali Naturalist
hing movement in Coimbatore facilitated by SACON
