Animal Kingdom (Kingdom Animalia)

Animals are multicellular and heterotrophic. Animal kingdom is most diverse than the plant kingdom.

BASIS OF CLASSIFICATION

1. Levels of organization

3 levels (based on organization of cells):

a. Cellular level of organization: Here the cells are arranged as loose cell aggregates. E.g. Poriferans.

b. Tissue level of organization: Here the cells are arranged into tissues. E.g. Cnidarians and Ctenophores.

c. Organ level of organization: Here the tissues are arranged into organs and the organs are associated to form organ systems. Each system performs a specific physiological function. E.g. All higher animals (from platyhelminthes to chordates).

Organ systems of different animals show complexities. E.g.

- Digestive system of cnidarians and platyhelminthes is incomplete (i.e. it has only a single opening which serves as both mouth and anus). Complete digestive system has 2 openings (mouth & anus).

Circulatory system is 2 types (open and closed).

2. Body symmetry

It is the arrangement of similar body parts on 2 sides of main axis of body. Based on symmetry animals are 2 types: Asymmetrical and Symmetrical.

a. Asymmetrical: Here, body cannot be divided into 2 similar parts. E.g. Certain Poriferans, Snails etc.

b. Symmetrical: Here, body can be divided into 2 similar parts. It is 2 types.

· Radial symmetry: Body can be divided into 2 similar parts by any plane along oral aboral axis of body. E.g. some Poriferans, Cnidarians, Ctenophores and Echinoderms.

· Bilateral symmetry: Body can be divided into 2 right and left halves by a section passing through the longitudinal axis. E.g. All vertebrates and many invertebrates. The body of bilaterally symmetrical animal has an upper or vertebral dorsal side, a lower ventral side, left and right lateral sides, anterior (cephalic) side and posterior (anal) side.

3. Germ layers

These are layers of gastrula from which all the body organs are formed. Based on the number of germ layers, animals are 2 types- Diploblastic and Triploblastic.

a. Diploblastic animals: 2 germ layers- outer ectoderm and inner endoderm. E.g. Sponges and Coelenterates.

b. Triploblastic animals: 3 germ layers- Outer ectoderm, middle mesoderm and inner endoderm. E.g. Flat worms to mammals.

4. Coelom (body cavity)

It is the space between body wall and gut wall. Coelom separates the muscles of gut and body wall. On the basis of nature of coelom animals are 3 types.

a. Acoelomate: No coelom. The space between body wall and digestive cavity is filled with matrix (parenchyma). E.g. Poriferans to platyhelminthes.

b. Pseudocoelomate: Here, blastocoel becomes the coelom. It is not lined by peritoneal layer. E.g. Aschelminthes.

c. Eucoelomate (True coelomate): Here, the coelom arises from the mesoderm. Coelom is lined by peritoneal layer and filled with coelomic fluid. E.g. Annelids to mammals.

Haemocoelomates: In Arthropods and mollusks, true coelom is reduced and filled with blood.

Functions of coelom:

· It accommodates visceral organs

· Coelomic fluid gives moist environment to visceral organs. Thus friction is minimized.

· Acts as shock absorber.

5. Metamerism (segmentation)

In some animals, the body is formed of similar parts (segments or metameres). This segmentation is called metamerism. E.g. Annelids, Arthropods.

In vertebrates: only internal metamerism.

6. Notochord

It is a supporting rod formed on the dorsal side during embryonic development in some animals. Animals with notochord are called chordates and those without notochord are called non-chordates

Phylum	Levels of organization	Germ layers	Symmetry	Coelom
Porifera	Cellular	Diploblastic	Asymmetrical/ radial	Acoelomate
Cnidaria	Tissue	-do-	Radial	-do-
Ctenophora	-do-	-do-	-do-	-do-
Platy-helminthes	Organ/ Organ system	Triploblastic	Bilateral	-do-
Aschelminthes	-do-	-do-	-do-	Pseudo-coelomate
Annelida	-do-	-do-	-do-	Coelomate
Arthropoda	-do-	-do-	-do-	-do-
Mollusca	-do-	-do-	-do-	-do-
Echinodermata	-do-	-do-	Radial	-do-
Hemichordata	-do-	-do-	Bilateral	-do-
Chordata	-do-	-do-	Bilateral	-do-

COMPARISON OF DIFFERENT PHYLA
(NON-CHORDATES)

Phyla Features	Porifera (Sponges)	Cnidaria (Coelenterata)	Ctenophora (Comb Jellies or sea walnuts)	Platyhelminthes (Flatworms)	Aschelminthes (Nemathel-minthes/ Roundworms)
Habit and habitat	Aquatic (mostly marine). Sedentary. Solitary or colonial.	Aquatic (mostly marine). Solitary or colonial. Sessile or free swimming	Exclusively marine. Solitary and pelagic.	Mostly endoparasites. Some are free-living. Mainly aquatic.	Free living, aquatic and terrestrial or parasitic in plants and animals.
Digestive system	Absent. Digestion is intracellular. Water transport (canal system)to gather food.	Incomplete. Intracellular and extracellular digestion.	Incomplete. Intracellular and extracellular digestion.	Incomplete.	Complete. Tubular alimentary canal with well-developed muscular pharynx.
Respiratory system	Absent. Respiration by canal system	Absent	Absent	Absent	Absent
Circulatory system	Absent. Circulation by canal system	Absent	Absent	Absent	Absent
Excretory system	Absent. Excretion by canal system.	Body surface.	Body surface.	Flame cells for excretion and Osmoregulation.	An excretory tube to remove body waste through excretory pore.
Nervous (Neural) system	Absent.	Only a network of neurons.	Only a network of neurons.	Present.	Present.
Reprodu-ctive system	Hermaphrodite. ARP by fragmentation. SRP by the formation of sperms and ova. Fertilization internal. Development is indirect.	Polyp reproduces asexually (budding) and medusa sexually. Fertilization external. Development is indirect.	Only SRP. Hermaphrodite. Fertilization external. Development is indirect.	ARP (by fragmentation) and SRP. Hermaphrodite. Fertilization is internal. Development is indirect (many larval stages).	Sexes are separate (Dioecious). Sexual reproduction. Internal fertilization. Development is direct or indirect.
Other features	Millions of minute pores (ostia). Spongocoel (body cavity) and canals are lined with choanocytes (collar cells). Body is supported by spicules and spongin fibres.	Tentacles with cnidoblasts (stinging cells). A central gastro-vascular cavity (coelenteron) with a single opening (mouth) on hypostome. Polyp & Medusa are 2 kinds of body forms. Show polymorphism and alternation of generation. Corals have a skeleton made up of CaCO₃.	Locomotion is by 8 vertical external rows of ciliated comb plates. Tentacles present. Shows Bioluminescence.	Unsegmented, dorso-ventrally flattened body (except in tape worms). Hooks and suckers in parasitic forms. Some of them absorb nutrients from the host through their body surface.	Syncitial epidermis. Thick cuticle. Sexual dimorphism (females are longer than males).
Examples	Sycon (Scypha), Spongilla (fresh water sponge), Euspongia (Bath sponge)	Hydra, Obelia, Physalia (Portugese man of war), Aurelia, Adamsia (Sea-anemone), Pennatula (Sea pen)), Gorgonia (Sea fan), Meandrina (Brain coral) etc.	Ctenoplana, Pleurobrachia	Taenia solium (Tape worm), Fasciola (Liver fluke), Planaria (shows high regeneration capacity).	Ascaris (Roundworm), Ancylostoma (Hookworm), Wuchereria (Filarial worm).

COMPARISON OF DIFFERENT PHYLA
(NON-CHORDATES)

Phyla Features	Annelida (Segmented worms)	Arthropoda (Joint-legged animals)	Mollusca (Soft bodied animals)	Echinodermata (Spiny skinned animals)	Hemichordata
Habit and habitat	Terrestrial, fresh water or marine. Free living or parasitic.	Cosmopolitan.	Generally aquatic. Few are terrestrial.	Exclusively marine.	Marine
Digestive system	Complete.	Complete and well developed.	Complete and well developed.	Complete. Ventral (lower) mouth and dorsal (upper) anus.	Complete
Respiratory system	Cutaneous respiration. Some have branchial (gill) respiration	Either by Gills or trachea, or book gills or book lungs.	Gills in aq. forms and pulmonary sac in terrestrial forms.	Dermal branchiae (gills) or papulae and tube feet.	Gills
Circulatory system	Closed type	Open type	Open type	Reduced and open type.	Open type
Excretory system	Nephridia for excretion and Osmoregulation.	Either Antennary glands or Malpighian tubules or coxal glands.	By Metanephridia	Absent. Diffusion through gills.	Proboscis gland
Nervous (Neural) system	Paired ganglia connected by lateral nerves to a double ventral nerve cord.	A nerve ring followed by a double ventral ganglionated nerve cord.	Paired ganglia and their connectives.	Present. No brain.	Simple
Reprodu-ctive system	SRP. Earthworms & leeches are hermaphrodites. Neries is dioecious. Development is indirect.	Sexes are separate. External fertilization in aq. forms. Internal fertilization in land forms. Mostly oviparous. Development is direct or indirect.	Sexes are separate. Oviparous. Development indirect.	Sexes are separate. Fertilization external. Development indirect. Ciliated free swimming larva.	Sexes are separate. Fertilization external. Development is indirect.
Other features	True segmentation. Longitudinal and circular muscles which help in locomotion. Locomotory organs are setae (in earthworm) or parapodia (in Neries).	Largest phylum. Jointed appendages. 3 regions: head, thorax & abdomen. Body is covered by chitinous cuticle (exoskeleton). Sensory organs (antennae, compound & simple eyes, statocysts or balance organs) are present.	Second largest phylum. Body has head, visceral mass (visceral hump) & muscular foot. Anterior head region has sensory tentacles. Univalve or bivalve calcareous shell. Feather-like gills have respiratory and excretory functions. Mantle & radula seen.	Body is covered with spines for protection. Head absent. Calcareous endoskeleton (ossicles) present. Water vascular system for locomotion, respiration & food capture & transport. Great power of autotomy and regeneration.	Worm-like cylindrical body composed of an anterior proboscis, a collar and a long trunk.
Examples	Pheretima (Earthworm), Hirudinaria (Blood sucking Leech), Neries.	Spider, Scorpion, Crab, Prawn, Insects etc. Economically important insects: Apis, Bombyx, Laccifer. Vectors: Mosquitoes (Anopheles, Culex & Aedes), Housefly etc. Gregarious pest: Locusta. Living fossil: Limulus (King crab)	Pila (Apple Snail), Achatina (Land snail), Pinctada (Pearl Oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea Hare), Dentalium (Tusk shell), Chaetopleura (Chiton)	Asterias (Starfish), Echinus (Sea Urchin), Echinocardium, Antedon (Sea Lily), Cucumaria (Sea Cucumber), Ophiura (Brittle Star).	Balanoglossus (Tongue worm), Saccoglossus

IMPORTANT TERMS

1. Canal system (water transport): A system in sponges. Here, water enters through minute pores (ostia) in the body wall into a central cavity (spongocoel), from where it goes out through osculum. Canal system is used for food gathering, gas exchange and removal of wastes.

2. Hermaphrodite: Male and female sex organs are seen in same individual.

3. Tentacles: Finger-like structures which surrounds the mouth of coelenterates. Used for food capture & defense.

4. Cnidoblasts (Cnidocytes or Stinging cells): These are certain ectodermal defensive cells with a capsule called nematocyst containing poisonous fluid. Mainly found in the tentacles. Cnidoblast is used for anchorage, defense and to capture prey.

5. Polyp & Medusa: 2 types of body forms in cnidarians. Polyp is tubular attached form, with upwardly directed mouth & tentacles. It represents the asexual stage. Medusa is umbrella like, free-swimming form, with downwardly directed mouth and tentacles. It represents the sexual stage.

6. Alternation of generation (Metagenesis): This means asexual polyp generation alternates with sexual medusa generation. E.g. Obelia.

7. Polymorphism: The phenomenon showing the presence of 2 or more morphologically and functionally different types of individuals in the colony of the same species. These different individuals are called zooids.

8. Bioluminescence: It is the property of some animals to emit light from the body.

9. Sexual dimorphism: Male and female show morphological difference.

10. Cephalothorax: In some Arthropods like Arachnids and crustaceans, head and thorax fuse to form a single region called Cephalothorax.

11. Ecdysis (moulting): Shedding of exoskeleton at intervals during the growth period. It enables the growth and expansion of the body.

12. Metamorphosis: Transformation of a larva into an adult. If the adult is lost some advanced characters of the larva it is called Retrogressive metamorphosis (It is the characteristic feature of Urochordata).

13. Radula: File-like rasping organ with transverse rows of teeth present in the mouth of molluscan. It is absent in bivalves.

14. Mantle (Pallium): The membrane which covers visceral hump (visceral mass) of molluscan. The mantle encloses a cavity called mantle cavity. Mantle secretes the shell.

15. Water vascular (ambulacral) system: A system (present in Echinodermata) in which sea water enters through a porous plate called madreporite. The water vascular system consists of radiating canals and tube feet (podia) filled with water. Their main function is locomotion and capture of food.

PHYLUM CHORDATA

These are animals with notochord, dorsal tubular nerve cord and pharyngeal gill slits. Notochord is a flexible rod located in the mid dorsal line between the alimentary canal and the nerve cord in the embryo.

Differences between Chordata and Non-chordata

Chordata	Non-chordata
1. Notochord is found in the embryonic stage	Absent
2. Central nervous system is dorsal, hollow and single	Ventral, solid and double
3. Pharyngeal gill slits present	Absent
4. Ventral heart	Dorsal heart (if present)
5. A post-anal tail is present	Absent

Phylum chordata is divided into 3 subphyla: Urochordata, Cephalochordata and Vertebrata

PROTOCHORDATA (ACRANIATA)		VERTEBRATA (CRANIATA)
Urochordata (Tunicata)	Cephalochordata	VERTEBRATA (CRANIATA)
· *Notochord* present only in larval tail · Body is covered by *test* made up of *tunicin* · Exclusively marine · *Retrogressive metamorphosis* · Hermaphrodite · E.g. Ascidia, Salpa, Doliolum etc	· Notochord from head to tail region and is persistent throughout the life · Exclusively marine · Fish-like · No definite coelom · Sexes are separate · E.g. Branchiostoma (Amphioxus or Lancelet)	· Possess notochord during the embryonic period · Notochord is replaced by a cartilaginous or bony *vertebral* *column* in the adult · *Ventral* muscular *heart* · *Kidneys* for excretion & osmoregulation · *Paired appendages* which may be fins or limbs

Vertebrata: Has 2 divisions- Agnatha and Gnathostomata

Agnatha (Jawless): Includes 1 class: Cyclostomata:

· All are ectoparasites on some fishes.

· Elongated body.

· 6-15 pairs of gill slits for respiration.

· Sucking and circular mouth without jaws.

· No scales and paired fins.

· Cartilaginous cranium and vertebral column.

· Circulation closed type.

· Marine, but migrate for spawning to fresh water. After spawning, they die. Their larvae, after metamorphosis, return to ocean.

· E.g. Petromyzon (Lamprey) and Myxine (Hagfish).

Gnathostomata (bears jaw):2 super classes (Pisces & Tetrapoda)
Pisces (Fishes- bears fins): 2 classes		Tetrapoda (bear limbs): 4 classes
Chondricthyes	Osteichthyes	Amphibia	Reptilia	Aves (Birds)	Mammalia
· Marine. · *Heterocercal* caudal fin. · *Cartilaginous* *endoskeleton.* · *Gill slits* without operculum. · Skin with *placoid scales.* · Teeth are modified placoid scales which are backwardly directed. · *No air bladder* so they have to swim constantly to avoid sinking. · Sexes are separate. In males pelvic fins bear *claspers.* · Internal fertilization. · Many of them *viviparous.* Examples Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray), Torpedo (Electric ray- have *electric* *organ)*.	· Marine & fresh water. · *Homocercal* caudal fin. · *Bony endoskeleton.* · Terminal mouth. · 4 pairs of *gills* covered by an *operculum* on each side. · Scales are Cycloid, ctenoid etc. · *Air bladder* for buoyancy. · Sexes are separate. · Fertilisation external. · Mostly *oviparous.* · Development direct. Examples Marine: Exocoetus (flying fish), Hippocampus (sea horse), Sardine, Mackeral, Tuna, Remora (sucker fish), Pomfret, Cybium Fresh water: Labeo (Rohu), Catla (Katla), Clarias (Magur), Tilapia, Anabas (Climbing perch) Aquarium: Betta (Fighting fish), Pterophyllum (Angel fish) etc.	· *Aquatic larval life* & *terrestrial adult life.* · For breeding they require a watery environment. · *Pentadactyl* limbs. · *Moist skin* without scales. · A *tympanum* represents ear. · Alimentary canal, urinary & reproductive tracts open into a *Cloaca* which opens to exterior · Respiration is by *gills* (in larva), *lungs* & *skin* · *3-chambered* heart (2 auricles + 1 ventricle). · *Poikilotherms* · Sexes are separate. Fertilisation external. · *Oviparous. · Development is indirect. Examples* Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Ichthyophis (Limbless amphibia), Ambystoma (Tiger salamander), Rhacophorus (Flying frog)	· Dry & cornified skin, epidermal *scales* or *scutes. Snakes and lizards shed their scales as skin cast. · Tympanum* represents ear · Limbs- 2 pairs (if present). · *3-chambered* heart (but a septum partially separates ventricle). Heart is *4-chambered* in crocodiles. · *Poikilotherms.* · Fertilisation internal. · *Oviparous.* · Development is direct. Examples Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator, Gavialis (gharial) Hemidactylus (Wall lizard), Sphenodon (Tautara), Draco (flying dragon or flying lizard), Phrynosoma (horned lizard), Varanus (monitor). Poisonous snakes: Naja (Cobra), Bangarus (Krait), Vipera (Viper), Crotalus (rattle snake), Enhydrina (sea snake) etc. Non-poisonous snakes: Python, Typhlos (blind snake), Dryophis (tree snake)	· Presence of *feathers.* · Possess *beak.* · Forelimbs are modified into *wings.* · Hind limbs have *scales* and are modified for walking, swimming, or clasping tree branches. · Skin is dry without glands except the *oil gland* at the base of the tail. · Long, hollow and *pneumatic* bones. · Digestive tract with additional chambers, the *crop* and *gizzard* · Heart is *4-chambered* · *Homoiotherms* (warm-blooded) · Double respiration. *Air sacs* connected to lungs. · No urinary bladder. · Fertilisation is internal. · *Oviparous.* · Development is direct. Examples Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Gullus (Fowl), Bubo (Owl), Aptenodytes (Penguin), Neophron (Vulture) etc.	· Presence of *mammary glands* (milk producing glands). · 2 pairs of limbs for walking, running, climbing, burrowing, swimming or flying. · Skin with *hair* · External ear *(Pinnae)* · *Heterodont, thecodont, diphyodont.* · *4-chambered* heart. · *Homoiotherms.* · Respiration by *lungs.* · Sexes are separate. · Fertilisation internal. · *Viviparous* (except Echidna and Platypus). · Development is direct. Examples Ornithorhynchus (Platypus), Macropus (Kangaroo), Pteropus (flying fox), Camelus (Camel), Macaca (Monkey), Rattus (Rat), Canis (dog), Felis (Cat), Elephas (Elephant), Equus (Horse), Delphinus (Common Dolphin), Balaenoptera (blue whale), Panthera tigris (Tiger), Panthera leo (lion)

Click here for PDF

Animal Kingdom (Kingdom Animalia)

3 Comments