ANIMALIA

 Animals are metazoans that differ from plants in a number of characteristics like absence of plastids, cell wall and central vacuole. There are about 1.2 million animal species which show great diversity in shape, size, colour, habits, habitat, structures etc. 

CHARACTERISTICS OF ANIMALIA 

- They are multicellular consumers of the ecosystem.

- They are made up of eukaryotic cells and have no cell wall, plastids, central vacuole and photosynthetic pigments.

- Lower animals exhibit cellular or tissue level of organization and higher animals have organ system level of organization.

- Mostly free living and some (sponges and several coelenterates) are fixed. 

- They take food by ingestion i.e., holozoic in nutrition and digestion takes place in an internal cavity. Some forms have absorptive nutrition and their digestive cavity is absent. The undigested food is removed by egestion.

-They have muscle cells (contraction and relaxation of body parts) and nerve cells (transmit nerve impulses). Porifers lack nerve cells.

- Lower animals have asexual and sexual reproduction. Higher animals have generally sexual reproduction.

- They exhibit meiosis and form gametes (only haploid stage) before fertilization.

- In adult stage of life cycle, they have typical diploid or triploid body. The zygote form a multicellular embryo. 

SOME GENERAL FEATURES OF ANIMALIA

1. Habitat: May be Aquatic or Terrestrial

(A) Aquatic Animals: fresh water or marine:

• Fresh Water Animals: Found in ponds, rivers,streams etc. e.g., snails, Amoeba, Paramecium, prawn etc. Marine Animals: Found in sea water where salt concentration is high e.g., all echinoderms, cartilage fishes and most of sponges and coelenterates.

• Pelagic : Animals live in sea or open water eg..jelly fishes. (a) Zooplankton : Drift with water currents e.g., invertebrates and their larvae.(b) Nektons: Swim actively even against water flow e.g., most of fishes.

• Benthic : Animals live at the bottom of sea e.g.,star fish. • Neuston: Animals float or swim on the surface of water.

• Seston: Living or non-living things that float orswim in water.

• Tripton: Non-living sestons float or swim in water. 

• Neritic : Animals are present in coastal water. 

• Sedentary (Sessile): Animals attached to the substratum:

(a) Epizoons: Animals fixed over other animals.

(b) Periphytons or Epiphytic: Fixed or attached over rooted plants

(c) Epilithic: Fixed on rocks or stones.

(B) Terrestrial Animals : Animals living on land: • Fossorial: Live inside burrows e.g., snake, earthworm, rabbit, duck billed platypus, etc.

• Arboreal: Live on the trees e.g., bats, apes,monkeys, most of birds etc. • Cursorial: Fast runners e.g., tiger, lion, horse,kangaroo, dog etc.

• Scansorial : Climb the walls or rocks e.g., wall lizards, flying squirrels ete.

• Aerial/Volant/Flying: Flying animals e.g., birds,bats, most of insects etc. • Cave dwellers: Reside in caves e.g., bats etc.

• Diurnal : Active during day hours e.g., butterfly, housefly etc.

• Nocturnal: Active during night hours e.g., moth, bats, owl etc.

• Vespertine: Active during evening hours e.g., birds etc.

• Auroral: Active during dawn e.g., earthworm etc. • Parasites: Live on or in the body of others e.g., fluke, tapeworm, ticks, mites etc. 

(C) Aggregations: Animals may be solitary living alone e.g., tapeworm, grasshopper) or gregarious (living in aggregations e.g., locust) or colonial (obligatory interdependence e.g., termites, honey bees etc.)

Animals usually aggregate during migration or mating. The group of these gregarious animals are known differently as

● Flock — Sheep, parrot

• Swarm — Locust, bees 

• Shoal — Fishes

• Herd — Cattle, zebra

• Troop — Monkey, lions

Their family may be

Monogamous: One female and one male e.g., Sparrow, white band gibbon etc.

Polygamous: One male with several females e.g., 

Matriarchy: Female is head of family e.g., African Deer etc.elephant etc.

Patriarchy: Male is head of family e.g., deer, zebraetc.

II. Levels or Grades of Organization

• Acellular/Protoplasmic Level: All the activities are functioned by one cell body e.g., Protozoa or acellular protists. 

• Cellular Level: These animals are made up of many cells which do not form definite tissues and there is no coordination among them. e.g.,mesozoans and Sponges.

• Cell-Tissue Level: These animals are made up of many cells which coordinate to perform a specific function. They form four types of tissues e.g., epithelial, connective, muscular and nervous tissues. Their body is made up of only two germ layers i.e., ectoderm and endoderm and are called diploblastic animals. e.g., Cnidaria or Coelenterata.

• Tissue-Organ Level: Their tissues are aggregated to form organs which have a more specialised function than tissues. They have a third cellular germ layer in between the ectoderm and endoderm i.e., mesoderm. They are triploblastic animals.e.g., Platyhelminthes.

• Organ-System Level : This is the highest level of organization. These animals are multicellular and several organs are associated to form a distinct system to perform a distinct function. e.g., from roundworms to mammals.

III. Body Plan

• Cell Aggregate Body Plan : The body is an aggregation of cells with meagre differentiation and no coordination. e.g., sponges.

• Blind Sac Body Plan : The body is like a sac or cavity with one opening which acts as both mouth and anus (incomplete alimentary canal) e.g., flatworms, coelenterates.

• Tube Within a Tube Plan : The body wall forms an outer tube and alimentary canal forms an inner or second tube. Alimentary canal is complete with two openings - anterior mouth (for ingestion) and posterior anus (for egestion). Their types are -

(a) Protostomous/Protostomy Plan : Mouth is formed earlier than anus from blastopore of archenteron in gastrula larva e.g., flatworms, roundworms, annelids, molluscs and arthropods. 1

(b) Deuterostomous/Deuterostomy Plan : Anus is formed first from blastopore of gastrula e.g., echinoderms, hemichordates, and chordates.

IV. Symmetry

It is the arrangement of body parts on two sides of main axis of body. Their types are

• Asymmetrical : Body is highly irregular that it cannot be divided in two similar parts by any plane e.g., certain sponges, snails.

• Symmetrical: The body is divided into two similar parts by one or more planes.

(a) Spherical/Universal Symmetry : The body is like a ball and can be divided into two equal parts by any plane passing through the centre of body e.g., some corals.

(b) Radial Symmetry : The body is in the form of a flat or cylinder (tall). It can be divided into equal halves by any plane passing through the centre from top to bottom e.g., some sponges, coelenterates, echinoderms. Their types are

(i) Tetramerous Radial Symmetry : Body parts arranged in 4 or multiple of 4 e.g., Jelly fish. 

(ii) Pentamerous Radial Symmetry: Body parts arranged in 5 or multiple of 5 e.g., Echinoderms.

(iii) Hexamerous Radial Symmetry : Body parts arranged in 6 or multiple of 6 e.g., Sea anemone.

(In sea anemone, body has biradial symmetry i.e., both radially and bilaterally symmetrical as parts formed by sagittal plane are not similar to parts produced by transverse plane.)

Their body is differentiated into oral (side which is having mouth) and aboral side (side opposite to oral side). Mostly they are sedentary i.e. attached to the substrate. Its advantage is that they collect the food from different directions.

(c) Bilateral symmetry: Body is divided into two equal halves by one plane only (mid-sagittal) all the vertebrates. The body has a anterior (head) end, posterior (tail) end, proximal (near site of body) end, distal (head/mouth region or away from the site of origin) end, dorsal (upper or vertebral) side, ventral (lower or towards the substratum during locomotion) side and two lateral (right and left) sides.

V. Cephalization

It is the differentiation of anterior or oral end of the animal due to concentration of brain and sense organs into a definite head. It is developed in flatworms and found in all phyla from platyhelminthes to chordata.

VI. Appendages

These are the out growth structures of the body which are used in feeding, locomotion and some other functions e.g., tentacles (coelenterates), parapodia (many annelids), foot (molluscs), antennae and legs (arthropods), tubefeet or podia (echinoderms), fins (fishes), limbs and wings (tetrapods). These may be paired (one on either side) or unpaired (e.g., dorsal fin and caudal fin in fishes).

VII. Metamerism/Segmentation

The repetition of internal body parts is called metamerism. Each segment is called a metamere or somite e.g., annelids, arthropods, molluscs and chordate. When the external division corresponds to internal division, it is called metameric segmentation. e.g., In annelids, the body is externally divided by annuli and internally by septa. In adult chordates, internal segmentation is exhibited by repetition of ribs, vertebral nerve, muscles and blood vessels. In arthropods, only external metamerism is present. In tapeworm, pseudometamerism or false segmentation is present because segmentation is not of embryonic origin.

In true/metameric segmentation, segments are always formed from posterior to anterior side whereas reverse is true for pseudosegmentation.

VIII. Germ Layers

All the tissues and organs develop from germ layers (layers of gastrula) as

Ectoderm - Outer layer ; Mesoderm - Middle layer; Endoderm - Inner layer. -- -

On the basis of number of germ layers, animals may be -

• Diploblastic : Two layers, outer ectoderm and inner endoderm or gastroderm. e.g., porifers and coelenterates, ctenophores.

• Triploblastic: All the three layers are presente.g., from platyhelminthes to mammals.

X. Body Temperatures

• Homeothermal/ Warm-blooded/Endothermal : Body temperature is constant and does not vary with surrounding temperature e.g., birds and mammals.

• Poikilothermal/Cold-blooded/Ectothemal: 

Body temperature is not constant, it varies with change in surrounding temperature e.g., invertebrates, fish, amphibians and reptiles. They defend in two ways.

(a) Hibernation/Winter sleep: Remains inactive during winters e.g., amphibians and lizards.

(b) Aestivation/Summer sleep: Remains inactive during hot summer e.g., amphibians. 

IX. Coelom/Body Cavity

It is the space between body wall and which is filled with a fluid and is lined by peritoneum derived from mesoderm. ,

• Acoelomate : No coelom. e.g., coelenterates, ctenophores, flatworms and proboscis worms.

• Pseudocoelomate/False coelomate : Developed from blastocoel. Coelom is present but not lined by peritoneal layer. e.g., roundworms (Ascaris).

• Eucoelomates/True coelomate : The body cavity is lined by peritoneal layers (outer side parietal epithelium and inner side visceral peritoneum). e.g., from annelids to mammals.

True Coelom is of two types on the basis of their origin.

• Schizocoel : Formed by splitting of mesodermal sheet e.g., annelids, arthropods and molluscs.

• In arthropods and molluscs, coelom is reduced, filled with blood and is called as haemocoel.

• Enterocoel: Formed from the enteron of gastrula e.g., echinoderms and chordates.

XI. Skeleton

It is the hard structure (frame) of body which provides shape, support and protection to the body. It is of two

1. Exoskeleton : Secreted by skin or ectoderm and is made up of non-living material e.g., chitinous plates or sclerites (arthropods), epidermal scales (reptiles), calcareous shell (molluscs), plates below skin (echinoderms), horny scales, feathers, claws, hair, nails, hoofs and horns (vertebrates).

2. Endoskeleton : Internal skeleton, produced by mesoderm or sometimes endoderm, may be living (cartilages and bones in vertebrates) or non-living (e.g., calcareous plates in echinoderms and calcareous or silicious spicules in porifers). 

XII. Digestive System

Includes ingestion, digestion and egestion of food. The alimentary canal is of two types -

1. Incomplete : Mouth present, anus absent e.g., coelenterates and flatworms.

2. Complete : Mouth for ingestion and anus for egestion e.g., roundworms to mammals.

XIII. Nutrition

Animals are heterotrophs (except some protozoans, they are autotroph). There are three types of feeding habits :

1. Ingestive/Holozoic : Herbivorous (plant feeder), carnivorous (animal feeder), omnivorous (animal and plant feeder), detrivorous (detritus feeder), scavenging (scavengers feeds on carrions), frugivorous (fruit eater), insectivorous (insect eater), cannibalism (eating other members of same species), sanguivorous (blood feeder), coprophagous (eating own faeces), coprozoic (feeding on faces of other animals) etc.

2. Saprozic : Live on the dead, decaying tissues e.g. fungi.

3. Parasitic : Living on or in another organism e.g., round worms, flukes etc.

XIV. Respiratory System

Exchange of gases takes place by general body surface (sponges, coelentrates), gills i.e., branchial respiration (crustaceans, mollusca, pisces), lungs i.e., pulmonary respiration (tetrapods), book lungs (arachnids), bookgills (Limulus), trachea (insects, centipedes, millipedes) and skin i.e., cutaneous respiration (annelids and amphibians).

XV. Circulatory System

It includes transport of material in the body. Their types are :

• Open Circulatory System : Blood flows in spaces or sinuses e.g., arthropods, molluscs except cephelopods, and leeches, tunicates.

Blood is conveyed directly to the organs without the formation of capillaries. These are usually low pressure systems so the blood to different organs is not well regulated. The blood returns to heart slowly.

• Closed Circulatory System : Blood flows inside the blood vessels e.g., annelids and all vertebrates. They are high pressure systems. The distribution of blood to different organs is well regulated. Blood is returned to the heart rapidly.

Blood may be colourless (insects), bluish due to stematics (Non-Chordates)

copper containing haemocyanin in plasma (molluscs), red due to haemoglobin in RBCs (vertebrates) or in plasma (annelids). Circulatory system is absent in Taenia.

XVI. Excretory System

It includes removal of nitrogenous wastes out of the body to maintain homeostasis. Many aquatic animals have no excretory organs e.g., porifers, coelenterates and echinoderms. There are various types of excretory organs. These are protonephridia or flame cells in platyhelminthes, renett cell or excretory canals in roundworms, nephridia in annelids, antennary or green glands in crustaceans, coxal glands and malpighian tubules in arachnids, malpighian tubules and urate cells in insects, centipedes and millipedes, renal organ or kidneys in molluscs and kidneys in vertebrates.

The animals may be of four types on the basis of nature of main nitrogenous waste.

1. Ammonotelic Animals : Excrete ammonia e.g., mostly aquatic invertebrates (sponges, coelenterates) and some aquatic vertebrates (bony fishes, tailed amphibians).

2. Ureotelic Animals : Nitrogenous waste is urea e.g., cartilage fishes (shark, rays), tailless amphibians, and mammals.

3. Uricotelic Animals : Excretory waste is uric acid e.g., insects, land snail, land reptiles and birds.

4. Aminotelic Animals : Excrete amino acids e.g., some molluscs and some echinoderms.

XVII. Nervous System

It controls and coordinates body functions. It is absent in porifers, diffuse type in coelenterates, ladder type in flatworms and roundworms, central nervous system is circum-pharyngeal nerve ring and ventral solid ganglionated nerve cord in annelids, central nervous system is circum-oesophageal nerve ring and a double, ventral, solid ganglionated nerve cord in arthropods, ganglia interconnected by commissures and connectives in molluscs, oral and aboral nerve rings and radial nerves in echinoderms and central nervous system is anterior broader brain, posterior longer and narrow spinal cord (CNS is dorsal, hollow and nonganglionated) in vertebrates.

XVIII. Reproduction

Animals may be

• Bisexual/Monoecious/Hermaphrodite: Male and female sex organs in one individual e.g., tapeworm, earthworm, leech, liverfluke. 

• Unisexual/dioecious : When an individual have either male or female sex organ e.g., frog, lizard, rabbit, man etc. In most of the cases they can be distinguished externally i.e., they show sexual dimorphism e.g., peacock and peahen, lion and lioness.

There are two methods of reproduction :

1. Asexual Methods : No formation and fusion of gametes e.g., binary fission, multiple fission, budding (Hydra) and fragmentation.

2. Sexual Methods: It involves formation and fusion of gametes. Fertilization may be external (enchinoderms, bony fishes and amphibians) or internal (land vertebrates and cartilage fishes). It may be cross fertilization (different animal) or self-fertilization (same animal). Cross fertilization takes place due to two conditions :

(i) Protandrous : Testes mature earlier than ovaries e.g., leech, earthworm.

(ii) Protogynous : Ovaries mature earlier than testes e.g., Scypha, Herdmania, human beings. Development may be direct i.e., young ones resembles the adult (earthworm, cockroach, human beings) or indirect i.e., young ones do ,