Animal Kingdom- Notes

  

4. ANIMAL KINGDOM

Animals are multicellular and heterotrophic organisms without cell wall and chlorophyll.

Kingdom Animalia includes 11 major phyla:

1.  Porifera	7.   Arthropoda
2.  Cnidaria	8.   Mollusca
3.  Ctenophora	9.   Echinodermata
4.  Platyhelminthes	10. Hemichordata
5.  Aschelminthes	11. Chordata
6.  Annelida

BASIS OF CLASSIFICATION

1. Levels of organization

Based on this, animals are grouped into four levels:

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

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

c.   Organ level of organization: Here, tissues are arranged into organs. E.g. Higher animals (Platyhelminthes to chordates).

d.   Organ system level of organization: Here, organs are associated to organ system. Each system performs a specific physiological function. E.g. Higher animals.

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

Digestive system is 2 types:

o  Incomplete:  It has only a single opening that acts as mouth & anus. Seen in Cnidaria and Platyhelminthes.

o  Complete: It has 2 openings (mouth & anus).

      Circulatory system is 2 types: open & closed.

2. Body symmetry

It is the arrangement of similar body parts on 2 sides of main axis of the body. So, body can be divided into 2 equal halves. Based on symmetry, animals are 3 types:

a.   Asymmetrical: Here, body cannot be divided into 2 equal halves. E.g. Most Poriferans, Snails etc.

b.   Radial symmetry: Here, body can be divided into 2 equal halves in any vertical plane along central axis (oral-aboral axis) of the body. E.g. some Poriferans, Cnidarians, Ctenophores and Echinoderms (adult).

c.   Bilateral symmetry: Here, body can be divided into equal right & left halves in only one plane. E.g. Platyhelminthes to Chordata (except adult Echinoderms).

       

Radial symmetry            Bilateral symmetry

3. Germinal layers (Embryonic layers)

These are layers of embryo 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. In between these layers, an undifferentiated jelly-like layer called mesoglea is present.  E.g. Cnidaria & Ctenophora.

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

(a)  Diploblastic (b)  Triploblastic

4. Coelom (body cavity)

It is the cavity lined by mesoderm. It is seen b/w body wall & gut wall. Coelom separates muscles of gut & body wall.

Based on the 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. Porifera to Platyhelminthes.

b.   Pseudocoelomate: False coelom. Here, the body cavity is not lined by mesoderm. Mesoderm is scattered pouches. E.g. Aschelminthes.

c.   Coelomate: True coelom. Here, the coelom arises from the mesoderm. E.g. Annelida to Chordata.

     Coelomate         Pseudocoelomate       Acoelomate                                       

5. Metamerism (segmentation)

It is the phenomenon in which the body or organs is externally and internally divided into repeated segments (metameres). E.g. Annelids (earthworm etc.), Arthropods.  

6. Notochord

It is a mesodermally derived 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.

GENERAL CHARACTERS OF DIFFERENT PHYLA (NON-CHORDATES)

Features	Porifera (Sponges)	Cnidaria (Coelenterata)	Ctenophora (Comb jellies or Sea walnuts)
Grades of organization	Cellular	Tissue	Tissue
Symmetry	Asymmetrical. Some are radial.	Radial	Radial
Germ layers	-	Diploblastic	Diploblastic
Coelom	Acoelomate	Acoelomate	Acoelomate
Habit and habitat	Aquatic (mostly marine). Sedentary. Solitary/colonial.	Aquatic (mostly marine). Sessile/free swimming. Solitary/colonial.	Exclusively marine. Solitary & pelagic
Digestive system	Absent. Intracellular digestion.	Incomplete. Intracellular & extracellular digestion.	Incomplete. Intracellular and extracellular digestion.
Respiratory system	Absent	Absent	Absent
Circulatory system	Absent	Absent	Absent
Reproduction	Asexual (fragmentation) & Sexual. Sexes are not separate (Hermaphrodite). Internal fertilization. Development is indirect (have larval stage).	Polyp reproduces asexually (budding) and medusa sexually. Most are separate sexes. External fertilization. Development is indirect.	Only Sexual. Hermaphrodite. External fertilization. Development is indirect.
Unique features	Water canal (water transport) system. Millions of ostia (pores). Spongocoel & canals are lined with choanocytes (collar cells). Body is supported by spicules and spongin fibres.	Tentacles with cnidoblasts. Gastro-vascular cavity (coelenteron) with an opening (mouth) on hypostome. Polyp & Medusa forms are seen. Some shows alternation of generation (metagenesis). Corals have skeleton (CaCO3).	Locomotion is by 8 vertical external rows of ciliated comb plates. Tentacles present. Shows Bioluminescence (ability to emit light from the body).
Examples	Sycon (Scypha), Spongilla (fresh water sponge), Euspongia (Bath sponge)	Hydra, Obelia, Aurelia (Jellyfish), Physalia (Portuguese man of war), Adamsia (Sea-anemone), Pennatula (Sea pen), Gorgonia (Sea fan), Meandrina (Brain coral)	Ctenoplana, Pleurobrachia

1.     Water canal system: 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.     Tentacles: Finger-like structures which surrounds the mouth of coelenterates. Used for food capture & defense.

3.     Cnidoblasts (Cnidocytes): These are stinging cells (on tentacle & body) with poison-filled capsule (nematocyst). Function: For anchorage, defense and to capture prey.

4.     Polyp & Medusa: 2 types of body forms in cnidarians.

Polyp is cylindrical & sessile. E.g. Hydra, Adamsia.

Medusa is umbrella like, free-swimming. E.g. Aurelia (Jelly fish).

5.     Alternation of generation (Metagenesis): The phenomenon in which polyps produce medusae asexually and medusae form the polyps sexually. E.g. Obelia.

        

         

GENERAL CHARACTERS OF DIFFERENT PHYLA (NON-CHORDATES)

Features	Platyhelminthes (Flatworms)	Aschelminthes (Roundworms)
Grades of organization	Organ & Organ system	Organ system
Symmetry	Bilateral	Bilateral
Germ layers	Triploblastic	Triploblastic
Coelom	Acoelomate	Pseudocoelomate
Habit and habitat	Mainly aquatic. Endoparasites. Some are free-living.	Aquatic and terrestrial. Free living or parasitic in plants & animals.
Digestive system	Incomplete	Complete. Tubular alimentary canal with well-developed muscular pharynx.
Respiratory system	Absent	Absent
Circulatory system	Absent	Absent
Reproduction	Asexual (fragmentation) and Sexual. Hermaphrodite. Internal Fertilization. Development is indirect. Many larval stages.	Dioecious (sexes are separate). Sexual reproduction. Internal fertilization. Development is direct or indirect.
Unique features	Dorso-ventrally flattened body. Excretion and osmo-regulation by Flame cells (protonephridia). Parasites have Hooks & suckers. Some absorb nutrients from the host through their body surface.	Body is circular in cross section. Thick cuticle. An excretory tube to remove body waste through excretory pore. Male & female are distinct. Females are longer than males.
Examples	Taenia solium (Tape worm), Fasciola (Liver fluke), Planaria (shows high regeneration capacity).	Ascaris (Roundworm), Ancylostoma (Hookworm), Wuchereria (Filarial worm).

                                                                                                                                                                                                                        

Examples for Platyhelminthes	Examples for Aschelminthes	Examples for Annelida
Examples for Arthropoda

 

 

GENERAL CHARACTERS OF DIFFERENT PHYLA (NON-CHORDATES)

Features	Annelida (Segmented or Ringed worms)	Arthropoda (Joint-legged animals)	Mollusca (Soft-bodied animals)
Grades of organization	Organ system	Organ system	Organ system
Symmetry	Bilateral	Bilateral	Bilateral
Germ layers	Triploblastic	Triploblastic	Triploblastic
Coelom	Coelomate	Coelomate	Coelomate
Habit and habitat	Terrestrial, fresh water or marine. Free living or parasitic.	Cosmopolitan	Aquatic. Few are terrestrial.
Digestive system	Complete	Complete	Complete
Respiratory system	Cutaneous respiration. Some have branchial (gill) respiration.	Gills/ book gills/ trachea/book lungs	Gills in aq. forms & pulmonary sac in terrestrial forms.
Circulatory system	Closed type	Open type	Open type
Reproduction	Sexual. Earthworms & leeches are monoecious. Neries is dioecious. Development is direct or indirect.	Mostly dioecious. Usually internal fertilization. Mostly oviparous. Development is direct or indirect.	Dioecious. Oviparous. Development is direct or indirect.
Unique features	Segmentation like rings. Longitudinal and circular muscles help in locomotion. Locomotory organs are setae (in earthworm) or parapodia (in Neries). Excretion by Nephridia. Paired ganglia connected by lateral nerves to a double ventral nerve cord.	Jointed appendages. Body has 3 regions: head, thorax & abdomen. Body is covered by chitinous cuticle (exoskeleton). Excretion by Malpighian tubules. Sensory organs are antennae, compound & simple eyes, statocysts (balance organs).	Body has head, visceral hump & muscular foot.  Head has sensory tentacles. Calcareous shell. Mantle: The soft membrane which covers visceral mass. Mantle cavity (Space b/w hump & mantle) contains feather-like gills for respiration & excretion. Radula: File-like rasping organ in the mouth. It is used for feeding.
Examples	Pheretima (earthworm), Hirudinaria (blood sucking Leech), Neries (aquatic. Parapodia for swimming).	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), Pinctada (Pearl Oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea Hare), Dentalium (Tusk shell), Chaetopleura (Chiton)

1.   Arthropoda is the largest phylum. Over two-thirds of all named species are arthropods.

2.   Mollusca is the second largest phylum.

                    

Examples for Mollusca                                        Examples for Echinodermata                              Example for Hemichordata

GENERAL CHARACTERS OF DIFFERENT PHYLA (NON-CHORDATES)

Features	Echinodermata (Spiny-skinned animals)	Hemichordata
Grades of organization	Organ system	Organ system
Symmetry	Adults radial. Larvae bilateral.	Bilateral
Germ layers	Triploblastic	Triploblastic
Coelom	Coelomate	Coelomate
Habit and habitat	Exclusively marine.	Exclusively marine.
Digestive system	Complete. Ventral mouth & dorsal anus.	Complete
Respiratory system	Skin gills. Water vascular system.	Gills
Circulatory system	Open type	Open type
Reproduction	Dioecious. External fertilization. Development is indirect. Free-swimming larva.	Dioecious. External fertilization. Development is indirect.
Unique features	They have an endoskeleton of calcareous ossicles (Spiny bodied). Water vascular system for locomotion, respiration, capture & transport of food. Excretory system absent.	Worm-like cylindrical body formed of anterior proboscis, a collar and a long trunk. Collar bears stomochord (a rudimentary structure similar to notochord). Excretion by Proboscis gland.
Examples	Asterias (Starfish), Echinus (Sea Urchin), Echinocardium, Antedon (Sea Lily), Cucumaria (Sea Cucumber), Ophiura (Brittle Star)	Balanoglossus (Tongue worm), Saccoglossus

Hemichordata was earlier considered as a sub-phylum of Chordata. Like chordates, it has pharyngeal gill slits.

PHYLUM CHORDATA

It includes 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 characteristics (Body plan)	Chordata	Non-Chordata
	1.    Notochord is found in the embryonic stage.	Absent
	2.    Central nervous system is dorsal, hollow & single.	Ventral, solid & double
	3.    Pharyngeal gill slits present.	Absent
	4.    Ventral heart.	Dorsal heart (if present)
	5.    Post-anal part (tail) is present.	Absent

 Phylum Chordata is classified into 3 subphyla: Urochordata, Cephalochordata & Vertebrata.

PROTOCHORDATA (ACRANIATA)		VERTEBRATA (CRANIATA)
Urochordata (Tunicata)	Cephalochordata
·   Notochord present only in larval tail. ·   Body is covered by test made up of tunicin. ·   Exclusively marine. ·   Hermaphrodite. ·   E.g. Ascidia, Salpa, Doliolum.	·   Notochord from head to tail region and is persistent throughout the life. ·   Fish-like body. ·   Exclusively marine. ·   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 (fins or limbs).

CLASSIFICATION OF VERTEBRATA

                                                                   

CLASS CYCLOSTOMATA

·     All are ectoparasites on some fishes.

·     Elongated body without scales and paired fins.

·     6-15 pairs of gill slits for respiration.

·     Sucking and circular mouth without jaws.

·     Cartilaginous cranium and vertebral column.

·     Circulation is 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).

SUPERCLASS PISCES (FISHES)

Class Chondricthyes (Cartilaginous fishes)	Class Osteichthyes (Bony fishes)
Marine. Stream-lined body. Predaceous.	Marine & fresh water. Stream-lined body.
Cartilaginous endoskeleton. Notochord is persistent throughout life.	Bony endoskeleton.
Ventral mouth.	Terminal mouth.
Gill slits without operculum. Powerful jaws.	4 pairs of gills covered by operculum on each side.
Skin with placoid scales. Teeth are modified placoid scales which are backwardly directed.	Scales are Cycloid, ctenoid etc.
No air bladder. So, they have to swim constantly to avoid sinking.	Air bladder for buoyancy.
Poikilotherms (cold-blooded): Animals that lack the capacity to regulate their body temperature.	Poikilotherms (cold-blooded).
Two-chambered heart (one auricle and one ventricle).	Two-chambered heart (one auricle and one ventricle).
Sexes are separate. In males, pelvic fins bear claspers. Internal fertilization. Many of them viviparous.	Sexes are separate. External fertilisation. Mostly oviparous. Development is direct.
Examples Scoliodon (Dogfish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray- has poison sting), Torpedo (Electric ray- has electric organ).	Examples ·   Marine: Exocoetus (flying fish), Hippocampus (seahorse). ·   Fresh water: Labeo (Rohu), Catla (Katla), Clarias (Magur). ·   Aquarium: Betta (Fighting fish), Pterophyllum (Angel fish).

SUPERCLASS TETRAPODA

Class Amphibia	Class Reptilia	Class Aves (Birds)	Class Mammalia
They live in aquatic & terrestrial habitats and need water for breeding.	Dry & cornified skin, epidermal scales or scutes.	Presence of feathers and beak. Forelimbs are modified into wings.	Presence of mammary glands (milk producing glands).
Body has head & trunk. Some have tail. Moist skin without scales. Most have 2 pairs of limbs.	Snakes and lizards shed their scales as skin cast. Limbs- 2 pairs (if present). Crawling mode of locomotion.	Dry skin without glands except the oil gland at the base of tail. Hind limbs have scales and are modified for walking, swimming or clasping tree branches. Hollow & pneumatic long bones.	Skin with hair.   2 pairs of limbs for walking, running, climbing, burrowing, swimming or flying.
Tympanum represents ear.	Tympanum represents ear.	Tympanum represents ear.	External ear (Pinnae).
3-chambered heart (2 auricles + 1 ventricle).	3-chambered heart (4- chambered in crocodiles).	4-chambered heart.	4-chambered heart.
Poikilotherms	Poikilotherms	Homoiotherms (warm-blooded): Ability to maintain a constant body temperature.	Homoiotherms
Alimentary canal, urinary & reproductive tracts open into a Cloaca which opens to exterior.	Well-developed alimentary canal.	Digestive tract has additional chambers, the crop & gizzard.	Well-developed alimentary canal. Dentition is Heterodont, thecodont & diphyodont.
Respiration is by gills (in larva), lungs & skin	Respiration by lungs.	Air sacs connected to lungs.	Respiration by lungs.
Sexes are separate. External fertilisation. Oviparous. Development is indirect.	Internal fertilisation. Oviparous. Development is direct.	Internal fertilisation. Oviparous. Development is direct.	Sexes are separate. Internal fertilisation. Viviparous (except Echidna and Platypus). Development is direct.
Examples Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Ichthyophis (Limbless amphibia)	Examples Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator, Hemidactylus (Wall lizard). Poisonous snakes: Naja (Cobra), Bangarus (Krait), Vipera (Viper) etc. Non-poisonous snakes: Python etc.	Examples Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture) etc.	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)