Kingdom Animalia comprises millions of animal species and studying them without a basic classification may lead to confusion. In addition to this, there are several new species of animals being constantly discovered. Classification is very essential for identification, naming and assigning a systematic position to the newly discovered species. Animal Kingdom is classified mainly based on the closely resembling characteristic features. Kingdom Animalia is characterised of eukaryotic, multicellular, heterotrophic organisms. They include about 35 phyla of which 11 are considered as major phyla. Almost 99 percent of animals are invertebrates or animals without backbone. The remaining represents vertebrates or animals with backbone. On the basis of the presence or absence of notochord (vertebral column), animals are also categorised into two major groups and they are non chordates and chordates.
Basis of classification
Multicellular organisms are structurally
and functionally different but yet they possess certain common fundamental features such as the arrangement of cell layers, the levels of organisation, nature of coelom, the presence or absence of segmentation, notochord and the organisation of the organ system.
Levels of organisation
All members of Kingdom Animalia are metazoans (multicellular animals) and exhibit different patterns of cellular organisation. The cells of the metazoans are not capable of
independent existence and exhibit division of labour. Among the metazoans, cells may be functionally isolated or similar kinds of cells may be grouped together to form tissues, organ and organ systems.
Cellular level of organisation This basic level of organisation is seen
in sponges. The cells in the sponges are arranged as loose aggregates and do not form tissues, i.e. they exhibit cellular level of organisation. There is division of labour among the cells and different types of cells are functionally isolated. In sponges, the outer layer is formed of pinacocytes (plate- like cells that maintain the size and structure of the sponge) and the inner layer is formed of choanocytes. These are flagellated collar cells that create and maintain water flow through the sponge thus facilitating respiratory and digestive functions.
Animals such as sponges lack nervous tissue and muscle tissue, what does this tell you about sponges?
Tissue level of organisation In some animals, cells that perform
similar functions are aggregated to form tissues. The cells of a tissue integrate in a highly coordinated fashion to perform a common function, due to the presence of nerve cells and sensory cells. This tissue level of organisation is exhibited in diploblastic animals like cnidarians. The formation of tissues is the first step towards evolution of body plan in animals (Hydra - Coelenterata).
Organ level of organisation Different kinds of tissues aggregate
to form an organ to perform a specific function. Organ level of organisation is a
further advancement over the tissue level of organisation and appears for the first time in the Phylum Platyhelminthes and seen in other higher phyla.
Organ system level of organisation The most efficient and highest level of
organisation among the animals is exhibited by flatworms, nematodes, annelids, arthropods, molluscs, echinoderms and chordates. The evolution of mesoderm in these animals has led to their structural complexity. The tissues are organised to form organs and organ systems. Each system is associated with a specific function and show organ system level of organisation. Highly specialized nerve and sensory cells coordinate and integrate the functions of the organ systems, which can be very primitive and simple or complex depending on the individual animal. For example, the digestive system of Platyhelminthes has only a single opening to the exterior which serves as both mouth and anus, and hence called an incomplete digestive system. From Aschelminthes to Chordates, all animals have a complete digestive system with two openings, the mouth and the anus.
Similarly, the circulatory system is of two types, the open type: in which the blood remains filled in tissue spaces due to the absence of blood capillaries. (arthropods, molluscs, echinoderms and urochordates) and the closed type: in which the blood is circulated through blood vessels of varying diameters (arteries, veins and capillaries) as in annelids, cephalochordates and vertebrates.
Diploblastic and Triploblastic organisation
During embryonic development, the tissues and organs of animals originate from two or three embryonic germ layers. On the basis of the origin and develop- ment, animals are classified into two cate- gories: Diploblastic and Triploblastic.
Animals in which the cells are arranged in two embryonic layers (Figure 2.1), the external ectoderm, and internal endoderm are called diploblastic animals. In these animals the ectoderm gives rise to the epidermis (the outer layer of the body wall) and endoderm gives rise to gastrodermis (tissue lining the gut cavity). An undifferentiated layer present between the ectoderm and endoderm is the mesoglea. (Corals, Jellyfish, Sea anemone)
Animals in which the developing embryo has three germinal layers are called triploblastic animals and consists of outer ectoderm (skin, hair, neuron, nail, teeth, etc), inner endoderm (gut, lung, liver) and middle mesoderm (muscle, bone, heart). Most of the triploblastic animals show organ system level of organisation (Flat worms to Chordates).
Germinal layers 2.1.png
Patterns of symmetry
Symmetry is the body arrangement
in which parts that lie on opposite side
of an axis are identical. An animal’s body plan results from the animal’s pattern of development. The simplest body plan is seen in sponges (Figure 2.2). They do not display symmetry and are asymmetrical. Such animals lack a definite body plan or are irregular shaped and any plane passing through the centre of the body does not divide them into two equal halves (Sponges). An asymmetrical body plan is also seen in adult gastropods (snails).
Asymmetry in sponges 2.2.png
Symmetrical animals have paired body parts that are arranged on either side of a plane passing through the central axis. When any plane passing through the central axis of the body divides an organism into two identical parts, it is called radial symmetry. Such radially symmetrical animals have a top and bottom side but no dorsal (back) and ventral (abdomen) side, no right and left side. They have a body plan in which the body parts are organised in a circle around an axis. It is the principal symmetry in diploblastic animals. Cnidarians such as sea anemone and corals (Figure 2.3) are radially symmetrical. However, triploblastic animals like echinoderms (e.g., starfish) have five planes of symmetry and show Pentamerous radial symmetry.
Animals which possess two pairs of symmetrical sides are said to be
Bilateral symmetry in Insects 2.5.png
biradially symmetrical (Figure 2.4). Biradial symmetry is a combination of radial and bilateral symmetry as seen in ctenophores. There are only two planes of symmetry, one through the longitudinal and sagittal axis and the other through the longitudinal and transverse axis. (e.g., Comb jellyfish – Pleurobrachia)
Animals which have two similar halves on either side of the central plane show bilateral symmetry (Figure 2.5). It is an advantageous type of symmetry in triploblastic animals, which helps in seeking food, locating mates and escaping
Figure. 2. 3 Radial and Pentamerous radial symmetry
Radial symmetry in sea anemone
Pentamerous radial symmetry in starfish
Biradial symmetry in comb jelly 2.4.png
from predators more efficiently. Animals that have dorsal and ventral sides, anterior and posterior ends, right and left sides are bilaterally symmetrical and exhibit cephalisation, in which the sensory and brain structures are concentrated at the anterior end of the animal.
Coelom
The presence of body cavity or coelom
is important in classifying animals. Most animals possess a body cavity between the body wall and the alimentary canal, and is lined with mesoderm (Figure 2.6)
Animals which do not possess a body cavity are called acoelomates. Since there is no body cavity in these animals their body is solid without a perivisceral cavity, this restricts the free movement of internal organs. (e.g., Flatworms)
In some animals, the body cavity is not fully lined by the mesodermal epithelium, but the mesoderm is formed as scattered pouches between the ectoderm and endoderm. Such a body cavity is called a pseudocoel and is filled with pseudocoelomic fluid. Animals that possess a pseudocoel are called pseudocoelomates e.g., Round worms. The pseudocoelomic fluid in the pseudocoelom acts as a hydrostatic skeleton and allows free movement of the visceral organs and for circulation of nutrients.
Eucoelom or true coelom is a fluid- filled cavity that develops within the mesoderm and is lined by mesodermal epithelium called peritoneum. Such animals with a true body cavity are called coelomates or eucoelomates. Based on the mode of formation of coelom, the eucoelomates are classified into two types, Schizocoelomates – in these animals the
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body cavity is formed by splitting of mesoderm. (e.g., annelids, arthropods, molluscs). In Enterocoelomate animals the body cavity is formed from the mesodermal pouches of archenteron. (e.g., Echinoderms, hemichordates and chordates) (Figure 2.7).
Development of Schizocoelom Ectoderm Gut
Endoderm
Early mesoderm
cells
Split in mesoderm Developing
coelom Development of Enterocelom
Early mesoderm
cells Gut
Ectoderm
Endoderm Separation of
pouches from gut Developing
coelom
Development of Schizocoelomata and Enterocoelomata 2.7.png
Diagrammatic repre 2.6.png
What is the advantage of true coelom over a pseudocoelom?
Segmentation and Notochord
In some animals, the body is externally and internally divided into a series of repeated units called segments with a serial repetition of some organs (Metamerism). The simplest form of segmentation is
found in Annelids in which each unit of the body is very similar to the next one. But in arthropods (cockroach), the segments may look different and has different functions.
Animals which possess notochord at any stage of their development are called chordates. Notochord is a mesodermally derived rod like structure formed on the dorsal side during embryonic development in some animals. Based on the presence or absence of notochord, animals are classified as chordates (Cephalochordates, Urochordates, Pisces to Mammalia) and nonchordates (Porifera to Hemichordata).
Classification of Kingdom Animalia
Animal kingdom is divided into two sub-kingdoms, the Parazoa and Eumetazoa based on their organisation. 1. Parazoa: These include the multicellular sponges and their cells are loosely aggregated and do not form tissues or organs. 2. Eumetazoa: These include multicellular animals with well defined tissues, which are organised as organs and organ systems. Eumetazoans includes two taxonomic levels called grades. They include Radiata and Bilateria.
sentation of coelom in animals
Kingdom
Cellular level
Radial
Bilateral
Tissue/Organ/ Organ system
Animalia (multicellular)
SymmetryLevels of Organisation
Grade 1: Radiata
Among the eumetazoa, a few animals have an organisation of two layers of cells, the outer ectoderm and inner endoderm, separated by a jelly like mesoglea. They are radially symmetrical and are diploblastic. Examples: Cnidarians (sea anemone, jelly fish) and Ctenophores (comb jellies).
Grade 2: Bilateria
The eumetazoans other than Radiata, show organ level of organisation and are bilaterally symmetrical and triploblastic. The grade Bilateria includes two taxonomic levels called Division.
Division 1: Protostomia (Proto: first; stomium: mouth)
Protostomia includes the eumetazoans in which the embryonic blastopore develops into mouth. This division includes three subdivisions namely acoelomata, pseudocoelomata and schizocoelomata.
Figure 2.8 Classification of Kingdom Anima
Porifera
Platyhelminthes
Aschelminthes
Annelida Arthropoda Mollusca Echinodermata Hemichordata Chordata
Without body cavity (aceolomates)
Coelenterata (Cnidaria)
Ctenophora
With false coelom (pseudocoelomates)
With true coelom (coelomates)
PhylumBody Cavity or Coelom
Division 2: Deuterostomia (deuteron: secondary; stomium: mouth)
Eumetazoans in which anus is formed from or near the blastopore and the mouth is formed away from the blastopore. It includes only one subdivision Enterocoelomata. They have a true coelom called enterocoel, formed from the archenteron.
Non Chordates (Invertebrata) 2.3.1 Phylum: Porifera
(L. poros-pore; ferre-to bear)
These pore bearing animals are commonly called sponges. They are aquatic, mostly marine, asymmetrical and a few species live in freshwaters. They are primitive, multicellular, sessile animals with cellular level of organisation in which the cells are loosely arranged. They are either radially symmetrical or asymmetrical animals.
They possess a water transport system or canal system where water enters through minute pores called ostia lining the body wall through which the water enters into a
lia based on common fundamental features
|——|
| Kingdom Levels of Symmetry Bo dy Cavity PhylumOrganisation or Co elom |
|---|
| Cellular levelP oriferaCoelenterataAnimalia (Cnidaria)(multicellular) RadialCtenophoraTiOrgan systessue/Organ/m Wi(aceolthouomatt body caes) vity PlatyhelminthesBilateral Wi(pseudocoelth false coelomatomes) AschelminthesAnnelidaArthropodaWith true coel om Mollusca(coelomates) EchinodermataHemichordataChordata |
central cavity (spongocoel) and goes out through the osculum. This water transport system is helpful in food gathering, circulation, respiration and removal of waste. Choanocytes or collar cells are special flagellated cells lining the spongocoel and the canals. The body is supported by a skeleton made up of calcareous and siliceous spicules or spongin or both. Nutrition is holozoic and intracellular. All sponges are hermaphrodites (i.e.) the ova and sperms are produced by the same individual. They also reproduce asexually by fragmentation or gemmule formation and sexually by the formation of gametes. Development is indirect with different types of larval stages such as parenchymula and amphiblastula.
Examples: Sycon (Scypha), Spongilla (fresh water sponge), Euspongia (bath sponge) Euplectella (Venus flower basket) (Figure 2.9).
Examples of Porifera 2.9.png
Sycon Hyalonema
Chalina Euplectella
The underwater sea bed is the new habitat where the discovery and development of Marine Pharmaceuticals are in peak. Anticancerous, Antimalarial drugs and other bioactive molecules have been isolated and tested successfully.
Phylum: Cnidaria
(G. knode -needle or sting cells) Cnidarians (were previously called
Coelenterata), are aquatic, sessile or free swimming, solitary or colonial forms with radial symmetry The name Cnidaria is derived from cnidocytes or cnidoblasts with stinging cells or nematocyst on tentacles. Cnidoblasts are used for anchorage, defense, and to capture the prey. Cnidarians are the first group of animals to exhibit tissue level organisation and are diploblastic. They have a central vascular cavity or coelenteron (serves both digestion and circulatory function) with a single opening called mouth or hypostome, which serves the process of ingestion and egestion. Digestion is both extracellular and intracellular. The nervous system is primitive and is formed of diffused nerve net. Cnidarians like corals have a skeleton made up of calcium carbonate. Cnidarians exhibit two basic body forms, polyp and medusa. The polyp forms are sessile and cylindrical (e.g. Hydra, Adamsia), whereas the medusa are umbrella shaped and free swimming. Cnidarians which exist
Examples of Cnidarians 2.10.png
Adamsia Pennatula
Meandrina Physalia
in both forms, also exhibit alternation of generations in their life cycle (Metagenesis). The polyp represents the asexual generation and medusa represents the sexual generation. Polyps produce medusa asexually and medusa forms polyps sexually. Development is indirect and includes a free swimming ciliated planula larva.
Examples: Physalia (Portugese man of war), Adamsia (Sea anemone), Pennatula (Sea pen), Meandrina (Brain coral) (Figure 2.10).
Compare the advantages and disadvantages of direct and indirect development.
Phylum: Ctenophora
(G. Ktenos -comb; phoros -bearing) Ctenophora are exclusively marine,
biradially symmetrical, diploblastic animals with tissue level of organisation. Though they are diploblastic, their mesoglea is different from that of cnidaria. It contains amoebocytes and smooth muscle cells. They have eight external rows of ciliated comb plates (comb jellies) which help in locomotion, hence commonly called comb jellies or sea walnuts. Bioluminescence (the ability of a living organism to emit light) is well marked in ctenophores. They lack nematocysts but possess special cells called lasso cells or colloblasts which help in food capture. Digestion is both extracellular and intracellular. Sexes are not separate (monoecious). They reproduce only by sexual means. Fertilization is external and development is indirect and includes a larval stage called cydippid larva. e.g., Pleurobrachia (Figure 2.11).
Examples : Pleurobrachia and Ctenoplana.
Example of Ctenophora- Pleurobrachia 2.11.png
Phylum: Platyhelminthes (Flatworms)
(G. Platy -broad or flat; helmin-worm) They have a dorsoventrally flattened
body and hence called flatworms. These animals are bilaterally symmetrical, triploblastic, acoelomate with organ system level of organisation. They show moderate cephalization and unidirectional movement. They are, mostly endoparasites of animals including human beings. Hooks and suckers are present in the parasitic forms and serve as organs of attachment. Their body is not segmented, but some exhibit pseudosegmentation. Some of the parasitic flatworms absorb nutrients directly from the host through their body surface. However, flatworms like liver fluke have an incomplete digestive system. Specialized excretory cells called flame cells help in osmoregulation and excretion. Sexes are not separate (monoecious); fertilisation is internal and development is through larval stages (miracidium, sporocyst, redia, cercaria). Polyembryony
is common in some flatworms (Liver flukes). Some members like Planaria show high regeneration capacity ( Figure 2.12).
Examples: Taenia solium (Tape worm), Fasciola hepatica (Liver fluke), Schistosoma (Blood fluke).
Phylum: Aschelminthes (Round Worms)
(G. Askes –cavity; helminths – worms) Previously called
Nematoda, this phylum is now named as Aschelminthes. The body of these worms is circular (round) in cross section and hence are called round worms. They are free living or parasitic on aquatic and terrestrial plants and animals. They are bilaterally symmetrical, triploblastic and pseudocoelomate animals with organ system level of organisation. The body is unsegmented and covered by a transparent,
Example Planaria Liverfl 2.12.png
Example Ascaris Filarial 2.13.png
tough and protective collagenous layer called cuticle. The alimentary canal is complete with a well developed mouth, muscular pharynx and anus. Excretory system consists of renette glands. Sexes are separate; and exhibit sexual dimorphism; often females are longer than males. Fertilisation is internal; majority are oviparous (e.g. Ascaris) few are ovoviviparous (Wuchereria). Development may be direct or indirect.
Examples. Ascaris lumbricoides (Round worm), Enterobius vermicularis (Pin worm), Wuchereria bancrofti (Filarial worm), Ancylostoma_a _deuodenale (Hook worm) (Figure 2.13).
Phylum: Annelida (Segmented worm)
(L. annulus -a ring, and G. edios- form) Annelids were the first segmented
animals to evolve. They are aquatic or terrestrial, free living but some are parasitic. They are triploblastic, bilaterally
s of Platyhelminthes uke Tapeworm
s of Aschelminthes worm Hook worm
symmetrical, schizocoelomates and exhibit organ system level of body organisation. The coelom with coelomic fluid creates a hydrostatic skeleton and aids in locomotion. Their elongated body is metamerically segmented and the body surface is divided into segment or metameres. Internally the segments are divided from one another by partitions called septa. This phenomenon is known as metamerism. The longitudinal and circular muscles in the body wall help in locomotion. Aquatic annelids like Nereis have lateral appendages called parapodia, which help in swimming. Chitinous setae in Earthworms, and suckers in Leech help in locomotion. The circulatory system is of closed type and the respiratory pigments are haemoglobin and chlorocruorin. Nervous system consists of paired ganglion connected by the lateral nerves to the double ventral nerve cord. They reproduce sexually. Development is direct or indirect and includes a trochophore larva. Some are monoecious (earthworms) while some are dioecious (Neries and Leech). (Figure 2.14)
Examples: Lampito mauritii (earthworm), Neries (sand worm), Hirudinaria (leech).
How is cephalisation advantageous to animals in finding food?
Exam Earthworm Nere 2.14.png
Filariasis has been a major public health problem in India next only to malaria. The disease was recorded in India as early as 6th century B.C. by the famous Indian physician, Susruta in his book Susruta Samhita. In 7 th century A.D., Madhavakara described signs and symptoms of the disese in his treatise ‘ Madhava Nidhana’ which holds good even today. In 1709, Clarke identified elephantoid legs in Cochin. The microfilariae in the peripheral blood was first identified by Lewis in 1872 in Calcutta (Kolkata).
Phylum: Arthropoda
(G**.** arthros- jointed; podes- feet) This is the largest phylum of the
Kingdom Animalia and includes the largest class called insecta (total species ranges from 2-10 million). They are bilaterally symmetrical, segmented, triploblastic and schizocoelomate animals with organ system grade of body organisation. They have jointed appendages which are used for locomotion, feeding and are sensory in function. Body is covered by chitinous exoskeleton for protection and to prevent water loss, It is shed off periodically by a process called moulting or ecdysis. The body consists of a head, thorax, and abdomen with a body
ples of Annelida is Leech
cavity called haemocoel. Respiratory organs are gills, book gills, book lungs and trachea. Circulatory system is of open type. Sensory organs like antennae, eyes (compound and simple), statocysts (organs of balance/ equilibrium) are present. Excretion takes place through malpighian tubules, green glands, coxal glands, etc. They are mostly dioecious and oviparous; fertilization is usually internal. Development may be direct or indirect. Life history includes many larval stages followed by metamorphosis.
Examples : Limulus (King crab, a living fossil), Palamnaeus (Scorpion), Eupagarus (Hermit crab), Apis (Honey bee), Musca (House fly), Vectors- Anopheles, Culex, Aedes (mosquitoes), Economically important insects - Apis- (Honey bee), Bombyx (Silk worm), Laccifer (Lac insects), Gregarious pest - Locusta (Locust) (Figure 2.15)
Spider silk is five times stronger than steel of the same diameter. It has been suggested that a Boeing 747 could be stopped in flight by a single pencil- width strand and spider silk is almost as strong as Kevlar, the toughest man-made polymer.
Examp 2.15.png
Prawn Hermit
Scorpion Spid
Phylum: Mollusca
(L. molluscs –soft bodied) This is the second largest animal
phylum. Molluscs are terrestrial and aquatic (marine or fresh water) and exhibit organ system level of body organisation. They are bilaterally symmetrical (except univalves eg. apple snail) triploblastic and coelomate animals. Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and a visceral hump or visceral mass. A soft layer of skin forms a mantle over the visceral hump. The space between the visceral mass and mantle (pallium) is called the mantle cavity in which a number of feather like gills (ctenidia) are present, which are respiratory in function. The digestive system is complete and mouth contains a rasping organ called radula with transverse rows of chitinous teeth for feeding (radula is absent in bivalves). The sense organs are tentacles, eyes and osphraidium (to test the purity of water and present in bivalves and gastropods). Excretory organs are nephridia. Open type of circulatory system is seen except for cephalopods such as squids, cuttle fishes and octopus. Blood contains haemocyanin, a copper containing
les of Arthropoda
crab Locust
er Limulus (Living fossil)
respiratory pigment. They are dioecious and oviparous. Development is indirect with a veliger larva (a modified trochophore larva).
Examples: Pila (Apple snail), Lamellidens (Mussel), Pinctada (Pearl oyster), Sepia (Cuttle fish), Loligo (Squid), Octopus (Devil fish) (Figure 2.16).
Examples of Mollusca 2.16.png
Pila Octopus
Squid Oyster
Marbled Cone Snail (Conus marmoreus)
This cone-shaped snail can deliver
dangerous venom which may result in vision loss, respiratory failure, muscle paralysis and eventually death. There is no anti-venom available.
Phylum Echinodermata
(G*. Echinos* – spiny; dermos –skin) All Echinoderms are marine animals.
The adults are radially symmetrical but the
larvae are bilaterally symmetrical. These animals have a mesodermal endoskeleton of calcareous ossicles and hence the name Echinodermata (spiny skin). They are exclusively marine with organ system level of organisation. The most distinctive feature of echinoderms is the presence of the water vascular system or ambulacral system with tube feet or podia, which helps in locomotion, capture and transport of food and respiration. The digestive system is complete with mouth on ventral side and anus on the dorsal side. Excretory organs are absent. The nervous system and sensory organs are poorly developed. The circulatory system is open type without heart and blood vessels. Sexes are separate. Reproduction is sexual and fertilization is external. Development is indirect with free swimming bilaterally symmetrical larval forms. Some echinoderms exhibit autotomy with remarkable powers of regeneration. e.g. Star fish. (Figure 2.17)
Examples: Asterias (Starfish or Sea star), Echinus (Sea-urchin), Antedon (Sea- lily), Cucumaria (Sea-cucumber), Ophiura (Brittle star)
Brittle star
Examples of Echinodermata 2.17.png
Starfish
Sea cucumber Sea urchin
Phylum: Hemichordata
(G.hemi –half; chorda-string) Hemichordates were earlier
treated as a subphylum of Chordata (or Prochordata). They are now regarded to be an independent phylum of invertebrates, close to Echinodermata. The animals of this group possess the characters of invertebrates as well as chordates.
This phylum consists of a small group of worm-like, soft marine animals, mostly tubiculous and commonly called the ‘acorn worms’ or ‘tongue worms’. They are bilaterally symmetrical, triploblastic and coelomate animals with organ system level of organisation. Their body is cylindrical and is divided into three regions, the anterior proboscis, a short collar and a long trunk. Most hemichordates are ciliary feeders. Their circulatory system is simple and open or lacune type with a dorsal heart. Respiration is through paired gill slits opening into the pharynx. Excretion is by a single proboscis gland or glomerulus situated in the proboscis. Nervous system is primitive. Sexes are separate and exhibit sexual mode of reproduction; Fertilization is external. Development is indirect with a free swimming tornaria larva.
Examples: Balanoglossus, Saccoglossus, Ptychodera flava (Indian Hemichordate found in Kurusadai islands in Tamilnadu) (Figure 2.18).
Example of 2.18.png
Hemichordata - Balanoglossus
Phylum: Chordata
(G. Chorda –string)
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:
Muscle segments Notochord
MouthPharyngeal slits or cleftsAnusMuscular,
post-anal tail
Dorsal, hollow
nerve cord
A Typical Chordate 2.19.png
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
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.
Subphylum: Urochordata or Tunicata
(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
Table. 1 Comparison of chordates and non-cho Chordates
Notochord is present Dorsal, hollow and single nerve cord Pharynx perforated by gill slits Heart is ventrally placed A post anal tail is present Alimentary canal is placed ventral to the nerve cord
Exampl Ascidia Salpa 2.20.png
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).
Examples: Ascidia, Salpa, Doliolum
Subphylum: Cephalochordata
( L*. Cephalo-* ‘head’ ; G. chorda ‘cord’.) Cephalochordates are marine forms,
found in shallow waters, leading a burrowing mode of life. They are small
rdates Non-chordates
Notochord is absent Double ventral solid nerve cord Gill slits absent Heart is dorsal or laterally placed or absent A post anal tail is absent Alimentary canal is placed dorsal to the nerve cord
es of Urochordata Doliolum
| C ho rd ates | Non-cho rd ates |
|---|---|
| Noto chord i s p res en t | Noto chord i s a bs en t |
| D ors a l, h ol lo w a nd sin g le n er ve co rd | D ouble v en t ra l s olid n er ve co rd |
| Phar y nx p er fora te d b y g i l l s li ts | Gi l l s li ts a bs en t |
| He ar t i s v en t ra l ly p l ace d | Hear t i s do rsal o r l atera lly p lace d o r a bs ent |
| A p os t a na l t ai l i s p res en t | A p os t a na l t ai l i s a bs en t |
| A lim en t ar y c ana l i s p l ace d v en t ra l t o t hener ve co rd | A lim en t ar y c ana l i s p l ace d do rs a l t o t hener ve co rd |
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).
Example: Branchiostoma (Amphioxus or lancelet)
Example of Cephalochordata - Amphioxus 2.21.png
Pharyngeal gill slits
Atrial pore
Cerebral vesicle Nerve cord
Buccal Mouth Gonads Anus
Notochord
Subphylum-Vertebrata
(L*. Vertebrus* –back bone )
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).
Class: Cyclostomata
(G.cyklos–circle; stomata -mouth)
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).
Examples of Cyclostomata 2.22.png
Lamprey Hag fish
Class: Chondrichthyes
(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.
Examples: Scoliodon (Shark), Trygon (Sting ray), Pristis (Saw fish) (Figure 2.23).
Class: Osteichthyes
(G. osteon –bone; ichthys -fish)
It includes both marine and freshwater fishes with bony endoskeleton and spindle
Examp 2.24.png
Flying fish Sea horse Angel
Example Shark Pris 2.23.png
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 mesonephric kidneys 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).
Examples: Exocoetus (Flying fish), Hippocampus (Sea horse), Labeo (Rohu), Catla (Catla), Echeneis (Sucker fish), Pterophyllum (Angel fish)
Class: Amphibia
(G. amphi-both; bios -life)
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
les of Osteichthyes
fish Carp Sucker fish
s of Chondrichthyes tis Sting ray
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.
Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), lcthyophis (Limbless amphibians) (Figure 2.25).
Examples of Amphibia 2.25.png
Frog Toad
Salamander Icthyophis (Caecilians)
Class: Reptilia
(L. repere or reptum – to creep or crawl)
They are mostly terrestrial animals and their body is covered by dry, and cornified skin with epidermal scales or
Turtles spend most of their life in the water Carapace is laterally compressed and streamlined. Mostly live in the water or are always found near it. Most of them have webbed feet.
TURTLE Vs
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.
Examples : Chelone (Turtle), Testudo (tortoise), Hemidactylus (House lizard), Chameleon (Tree lizard), Calotes (Garden lizard), Draco (Flying lizard), Crocodilus (crocodile), Poisonous snakes - Naja (Cobra), Bangarus (Krait), Vipera (Viper) (Figure 2.26).
Examples of Reptiles 2.26.png
King cobra Draco (Flying Lizard)
Crocodile Chameleon
Tortoises spend most of their life on land. Carapace is usually dome-shaped. These are primarily terrestrial. Feet are short and sturdy with bent legs.
TORTOISE
Class Aves
(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 (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.
Examples Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture), Chalcophaps indica (Tamilnadu state bird, Common Emerald Dove) (Figure 2.27).
Examples of Aves 2.27.png
VultureCommon Emerald Dove (Tamil Nadu State Bird)
PenguinHumming Bird
Class: Mammalia
(L. Mamma – Breast)
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.
Examples Oviparous- Ornithorhynchus (Platypus), Viviparous- Macropus (Kangaroo), Pteropus (Flying
Exam 2.28.png
Monkeys Elepha
PlatypDolphin
Bat Pang
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.
fox), Macaca (Monkey), Canis (Dog), Felis (Cat), Elephas (Elephant), Equus (Horse), Delphinus (Common dolphin) Balaenoptera (Blue whale), Panthera tigris (Tiger), Panther leo (Lion), Homo sapiens (Human) Bos (Cattle) (Figure 2.28).
Sálim Moizuddin Abdul Ali 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