Habits:

• Frogs are non-poisonous, harmless and usually silent animals.
• Unless disturbed, the detection of frog’s presence is difficult.
• Along with being an excellent jumper, it is very agile

Habitat of frog:

• Frogs commonly dwell in or near water and in relatively damp areas on land.
• Indian bull frog (Rana tigrina) lives in or near permanent freshwater lakes, ponds and streams.
• It spends its most of the time in the water.
• The reasons for why the frog reside near the water are:
• To keep skin moist so as to perform cutaneous respiration.
• To escape from enemies by jumping into the water.
• Their oviposition, fertilization and embryonic development takes place in water.

Locomotion of frog:

• Frog locomotes in two ways, by leaping on ground and swimming in water.
• Its muscular and endoskeletal systems have been modified to do so.
• Leaping:
  • While resting on land, frog’s short forelimbs are kept upright and the long hind limbs are folded in the manner of Z.
  • The hind limbs are powerful.
  • As the front part is inclined upwards during normal resting position, it is termed as squatting posture.
  • The sudden extension of hind limbs during leaping acts as springs throwing the body to air.
  • In a single jump, frog can jump a distance of 1.5 to 2 meters.
  • The forelimbs act as shock absorbers on landing back to the ground.
  • The forelimbs also manipulate and adjust the direction of the jump.
• Swimming:
  • The swimming of frog in water is possible because of the powerful backwards thrusts of its hind limbs that act like propellers.
  • In course of their backward strokes, the toes are spread apart and the broad webs push against water, leading the body forward.
  • When the frog is paddling around leisurely, the right and left forelimbs move alternately.
  • Forelimbs carry out two roles i.e. assist in propelling and in guiding the direction of movement.
  • Only the tip of snout carrying nostrils is exposed, when frog comes to surface to breathe, or just float. In this time, the fore and hind limbs are extended in water.
  • If disturbed in this position, it dives under water right away.

Feeding habit of frog:

• Being carnivorous in nature, it feeds on living insects, worms, molluscs and tadpoles.
• It catches its prey by a sudden flip of its protrusible sticky tongue which is attached at the front end and is free behind.
• It ignores motionless object or food.
• It doesn’t chew, but swallows whole food.

Croaking sound of frog:

• Croaking is a term given for characteristic noise or sound produced by frogs.
• It is commonly heard during rains which is its breeding season.
• It is considered as mating call.
• The air is forced from lungs over vocal cords into mouth cavity and is returned back again. This is how croaking sound is produced.
• Croaking can be done under water and on land as well.
• Croaking is heard louder in males due to presence of a pair of distensible balloon-like loose skin folds on throat, called vocal sacs.
• Vocal sacs act as resonators.

Hibernation and aestivation in Frog:

• As frogs are cold-blooded animals, the body temperature alters with that of surrounding.
• In the time of adverse environmental conditions such as cold winter and hot summer days, frogs hide themselves in the soft damp bottom mud for protection.
• They now stop feeding and become metabolically inactive.
• They survive on glycogen and fat stored in their bodies.
• Pulmonary respiration is suspended.
• Cutaneous respiration through moist skin is sufficient.
• This condition of dormancy or suspension of liveliness is termed as hibernation or ‘winter sleep’ during winter and aestivation or ‘summer sleep’ in summer.
• As soon as the cold winter or hot summer ends, the frogs return back to their normal active life.

Camouflage adaptation in frog:

• Frogs have the color changing ability of skin to match with that of surroundings.
• It helps them to escape from enemies by remaining unnoticeable.
• This type of protective coloration is termed as camouflage.
• The change in color is possible due to dispersion or concentration of special amoeboid pigment cells in their skin.

Breeding in frog:

• As soon as the rainy season starts, frog comes out from aestivation.
• It starts breeding immediately which lasts from July to September.
• Males gather in shallow waters and attract females by croaking which is often a sex call.
• The male mounts upon the back of the female and grasps firmly around her thorax by his forelegs.
• The males have nuptial pads on the bases of inner fingers which are fully developed during breeding season.
• It helps them in holding the slippery female.
• Amplexus is the term given for this sexual embrace.
• Amplexus continues for several days till the female deposits several hundred ova or eggs through her cloaca into water.
• Milt or seminal fluid is discharged by males over eggs.
•  Milt or seminal fluid contains spermatozoa that fertilizes eggs.
• Hence, fertilization is external.
• Now, the male releases grip, leaving the female.
• Frog’s spawn (mass of eggs) is embedded in a gelatinous material which on contact with water swells into a protective transparent jelly.
• The fertilized eggs or zygotes develop into tadpoles within two weeks of time.
• Tadpoles are free-swimming aquatic larvae.
• These tadpoles undergo metamorphosis to become adult terrestrial frogs.

Enemies of frog:

• The number or frogs and tadpoles are reduced by several natural enemies.
• The major enemies are snakes, mongooses, turtles, racoons, crows, vultures, aquatic birds, fishes, other amphibians and man.
• Frogs also becomes host for different kinds of parasites such as protozoans (Opalina, Nyctotherus, Balantidium, Trichomonas, Entamoeba), lung flukes (Haemotoloechus, Pneumobites) and nematodes (Rhabdias).

Economic importance of frog:

• As a vertebrate type, frog is studied widely in laboratory.
• It is also used for researches in Physiology, Pharmacology and human pregnancy tests.
• It is also used as a fish bait.
• It is regarded as farmer’s friend as it feeds on insects harmful for crops.
• The hindlegs of frogs are used as food source by men.
• In some parts of world, they are reared at farms.

External features of Frog:

1. Morphology of frog

• Shape and size:
  • Body of a frog is somewhat spindle-shaped, pointed anteriorly and rounded posteriorly.
  • It is slightly flattened dorsoventrally.
  • It is streamlined so that it offers least resistance while swimming.
  • Body is divisible into distinct head, trunk and limbs.
  • Both neck and tail are absent.
  • Size varies from 12 to 18cm in length and 5 to 8cm in width.
• Skin and color:
  • Skin of frog is thin, moist and smooth.
  • It fits loosely on the body.
  • Skin lacks placoid scales or any other hard exoskeletal parts.
  • Dermal plicae (dorso-lateral folds or thickenings) is present on skin of back.
• Head:
  • Head of frog is flat, roughly triangular in outline and has a short blunt anterior snout terminating in a wide transverse mouth.
  • Just above the mouth, at the tip of the snout, two openings are present.
  • These openings are termed as the external nares or external nostrils which lie dorsally. It helps in respiration.
  • On top of head, two very large, spherical and protruding eyes are present dorso-laterally.
  • These eyes make marked prominences on the roof of buccal cavity when pressed downwards.
  • Eyes do not rest on any bone unlike higher animals.
  • Upper eyelid is almost immovable and is thick and pigmented.
  • Lower eyelid is freely moveable and is thin and semitransparent.
  • A transparent third eyelid or nictitating membrane arises from the lower eyelid.
  • This membrane covers and protects eyes during swimming and prevents from drying in air.
  • Vestigial pineal eye is present just in front of eyes.
  • It is represented by median light-colored patch or brow spot.
  • The ear drum or tympanum is present behind and below each eye.
  • The eardrum is a conspicuous, flat and deeply pigmented circular patch that receives sound waves.
  • Frog lacks external ear.
  • In male, vocal sacs are present in form of two bluish patches of skin.
  • Vocal sacs act as resonators to intensify sound of croaking during breeding season.
• Trunk:
  • Head is broadly joined behind with the flat trunk.
  • Trunk is ovoid in structure.
  • Its back is raised in the middle in a characteristic sacral prominence of hump.
  • It is clearly seen when the frog is squatting.
  • A small circular cloacal aperture or vent is present at the posterior end of trunk.
  • It serves for the discharge of faecal and urinary wastes as well as reproductive products (ova or sperm).
• Limbs:
  • Laterally, the trunk bears two pairs of limbs or appendages.
  • The short forelimbs arise anteriorly from trunk just behind the head.
  • Each forelimb consists of:
    • The upper arm (brachium)
    • Forearm (antebrachium)
    • Wrist (carpus)
    • Hand (manus) bearing 4 digits without web.
    • Thumb or pollex is vestigial.
  • In case of male frog, the base of first inner finger is thickened, especially in breeding season. It forms the nuptial pad for clasping the female during amplexus.
  • The much elongated and powerful hind limbs or legs arise close together posteriorly from trunk.
  • Each hind limb consists of:
    •  the thigh
    •  shank (crus)
    • much lengthened ankle (tarsus) and large foot (pes)
  • Foot has 5 slender clawless toes connected by broad thin webs of skin which assist in swimming.
  • A rudimentary sixth digit called prehaullex is present in addition to it.
  • It is enclosed within the skin and is not seen as sixth digit.

2. Sexual dimorphism in frog:

• There are some variations in external characters by which male and female frogs can be differentiated:
• Males are normally smaller in size and darker in color than females.
• Males are slim while females are stout, especially when they bear eggs.
• Males croak loudly as they have vocal sacs whereas vocal sacs are absent in females. The eardrum is larger in male.
• Males have swollen copulatory or nuptial pads on inner fingers whereas it is lacking in females.
• During amplexus, the upper one is male and the lower one is female.

3. Coelom and viscera of frog:

• A large body cavity or coelom is present inside the trunk of frog.
• It consists most of the internal organs or viscera.
• A thin, transparent membrane of mesodermal origin is termed as the peritoneum.
• It lines the body cavity (parietal peritoneum) and also covers the internal organs (visceral peritoneum).
• Most digestive and reproductive organs are suspended from mid-dorsal body wall by mesenteries (double layers of peritoneum).
•  Through mesenteries, nerves and blood vessels connect to the organs.
• A watery coelomic fluid fills the body cavity.
• It lubricates the viscera and prevents from friction.
• Pericardium encloses the heart.
• Pericardium is a special coelomic cavity.
• The remaining coelom is termed as perivisceral or abdominal cavity.
• Pericardio-peritoneal canal is absent.

4. Endoskeleton of frog:

• There is absence of exoskeleton in modern Amphibia.
• The frog has well developed endoskeleton.
• It consists largely of bone and cartilage.

Frog: Characteristic features and morphology

The post Frog: Characteristic features and morphology appeared first on Online Biology Notes.

Some important branches of biology are given below:

A

Anatomy: Study of internal structure

Anthropology: Study of Human beings

Arthrology: Study of Joints of bones

B

Bacteriology: Study of Bacteria

Biochemistry: Study of Chemical of organism

Bioclimatology: Study of influence of climates on Organism

Biogeography: Study of Distribution of plants and animals

Bioinformatics: Study of applied information technology to life sciences; documentation data

Botany: Study of plant science

C

Carcinomalogy: Study of Cancer

Cardiology: Study of Heart

Cell Biology: Study of Cell

Craniology: Study of Skull

Crybiology: Study of Life at low temperature

D

Dermatology: Study of Skin

Developmental biology:  Study of development of organism from zygote to full structure

E

Embryology: Study of Embryonic development of organisms

Entomology: Study of Insects

Epidemiology: Study of Epidemic diseases

Enthology: Study of Variety of human race

Ethology: Study of Animal behavior

Etiology: Study of Causes of diseases

Eugenics: Study of Improvement of human race by altering its genetic composition

Evolution: Study of Origin and evolution of life

Exobiology: Study of Life on other planets

G

Genetic: Study of s Heredity and variations

Gynaecology: Study of Treatment of women’s diseases

H

Haematology: Study of Blood

Helminthology: Study of Helminthes or worms

Hepatology: Study of Liver

Herpetology: Study of Amphibians and reptiles

I

Ichthyology: Study of Fishes

Integrative biology: Study of whole organisms

Immunology: Study of structure and function of immune system

K

Karyology: Study of Nucleus

L

Limnology: Study of Fresh water

M

Malacology: Study of Snail

Mastology: Study of Mammary glands

Morphology: Study of Form and structure

Mycology: Study of Fungi

N

Nematology: Study of Nematodes

Nephrology: Study of Kidneys

O

Oology: Study of Eggs

Ophilogy: Study of Snakes

Ophthalmology: Study of Eyes

Ornithology: Study of Birds

Osteology: Study of Bones

P

Paleontology: Study of Fossils

Parasitology: Study of Parasites

Pathology: Study of diseases

Physiology: Study of Life processes and functions of organisms.

Protozoology: Study of protozoa

S

Saurology: Study of Lizards

Serology: Study of Blood.

Synecology: Study of Community in environment

T

Taxanomy: Study of Identification, nomenclature and classification of organisms

V

Virology: study of viruses

Z

Zoology: Study of animal science

Branches of Biology

The post Branches of Biology appeared first on Online Biology Notes.

1. (Noton; back and chorda; cord).
2. Kingdom: Animalia
3. Presence of a notochord
4. They are backboned animals (vertebrates),
5. Most of the living chordates are familiar vertebrate animals.
6. Presence of dorsal hollow nerve cord
7. Blood vascular system: Present, closed type
8. Ventral heart, hepatic portal system and RBC are present.
9. Germ layer: Triploblastic.
10. Symmetry: bilateral symmetry body.
11. Coelom: Present. Well developed
12. Presence of gill (pharyngeal) slits
13. Presence of post anal tail

Phylum Chordata is divided into four sub-phylum:

1. Hemichordata,
2. Urochordata,
3. Cephalochordata
4. vertebrata or Craniata

1. Sub-Phylum: Hemichordata

• (hemi: half; chorde: cord)
• Habitat: exclusively marine
• Notochord present only in anterior region
• Notochord is also known as Buccal diverticulum
• Body is soft worm like
• Body is divided into Probosis, collar and trunk
• Sexes are separate
• Fertilization: external
• Examples: Balanoglossus, Cephalodiscus, Atubaria

2. Sub-phylum: Urochordata

• ( uros: tail; chorde: cord)
• Habitat: marine
• Notochord present only in tail region of tadpole larvae
• Adult lack tail and organ for locomotion
• Sex: Hermaphrodite
• Fertilization: Cross and external
• Development: indirect
• Examples: Hermania, Salpa, Doliolum

3. Sub-phylum: Cephalochordate

• (kephalo: head; chorde: cord)
• Notochord present from head to tail and persist throughout life
• Pharynx is well developed with numerous gill slits
• Coelom present
• Body resemble small fish like
• Circulatory system well developed
• Sexes: separate
• Fertilization: external
• Development: indirect
• Examples; Amphioxus, Asymmetron

4. Subphylum: Vertebrata

• (vertebra: backbone)
• Also known as craniate)
• Habitat: Aquatic as well as terrestrial
• Notochord is replaced by vertebrae or backbone
• Germ layer: triploblastic
• Symmetry: bilateral
• Body divided into head, trunk and tail
• Excretion: a pair of kidney
• Circulation system: closed type
• Blood pigment present
• Sexes: separate
• Fertilization; internal or external

The vertebrata is sub-divided into two divisions:

i. Agnatha (Lack jaw) and

ii. Gnathostomata (Possess jaw).

• The Gnathostomata are further divided into six classes:
• Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia.

Characteristics of Phylum Chordata

The post Phylum Chordata characteristics appeared first on Online Biology Notes.

The post Difference between Chondrichthyes (cartilaginous fish) and Osteichthyes (bony fish) appeared first on Online Biology Notes.

Other major differences between Prokaryotic cells and eukaryotic cells are as follows,

Major Difference between Prokaryotic cells and Eukaryotic cells

The post Major Difference between Prokaryotic cells and Eukaryotic cells appeared first on Online Biology Notes.

• In ecology, it is an animal behaviour of mass movement of animals from one place to another.
• The purposes for migration varies accordingly with the types of animals.
• Migratory behaviour of fish is a regular phenomenon. Their journey is purposed mainly for feeding and reproduction.

Types fish migration on the basis of needs:

1. Alimentary or Feeding migration: migration for search of feeding ground. It occur when food resources get exhausted.
2. Gametic or spwaning migration: it occur during breeding season in search for the suitable spawning ground.
3. Climatic or seasonal migration: migration in search for suitable climatic condition.
4. Osmo-regulatory migration: migration for water and electrolytes balance from sea to fresh water and vice-versa.
5. Juvenile migration: it is larval migration from spawning ground to the feeding habitats of their parent.

Movement of fishes during the migration

1. Drifting movement: It is a passive movement of fish along with water currents
2. Dispersal movement: It is a random locomotory movement of fish from a uniform habitat to diverse direction
3. Swimming movement: It is an orientated movement of fish either toward or away from the source of stimulus
4. Denatant and Contranatant movement: It is an active swimming movement. Denatant movement is swimming with the water current while contrantant movement is swimming against water current

Types of fish migration

The migration of some fishes is a regular journey and is truly an innate animal behaviour. Fish migration are classified into following types:

1. Diadromous migration:

• it is the migration of fish between sea and fresh water.
• As we know, most of the fishes are restricted to either fresh water or sea water. Changes in habitat may causes osmotic imbalance in those fishes. However some fishes regularly migrate between sea and fresh water and have perfect osmotic balance, they are the true migratory fish.
• This migration is of two types-

i. Anadromous migration:

• it is the migration of marine fishes from sea to fresh water for spawning.
• Fishes spend most of their life living and feeding in sea.
• They only migrate during breeding season to the river for spawning ground.
• Eg. Salmon, Hisla, Lamprey etc.

• Salmon migrate for breeding during winter from sea to river. While migrating, some physiological changes occurs:
• – stops feeding during journey
• – changes colour from silver to dull reddish brown
• – gonads mature
• They select suitable spawning ground and make a saucer-like nest in which female lays eggs and male releases smelt over them. Juvenile larva hatched out from the egg known as Alevins. Alveins then transform into parr and metamorphosed into adult when return to the sea.

ii. Catadronous migration:

• It is the migration of fresh water fishes from river to sea during breeding season for spawning. Eg. Eel (Anguilla spp)
• Both European eel (Anguilla anguilla or Anguilla vulgaris) and the American eel (Anguilla rostrata) migrate from the continental rivers to Sargasso Sea off Bermuda in south Atlantic for spawning, crossing Atlantic Ocean.
• Before and during migration some physiological changes occur in their bodies:
• – deposit large amount of fat in their bodies which serves as reserve food during the journey
• – Colour changes from yellow to metallic silvery grey.
• – Digestive tract shrinks and stops feeding
• – Eyes get enlarged and vision sharpens. Other sensory organs also become sensitive.
• – Skin serves respiratory organ.
• – Gonads get matured and enlarged.
• The lay eggs in suitable spawning ground and are fertilized by males. After spawning they die. The larva hatch out and develop into young ell and finally return to river.

2. Potamodromous migration:

• it is fresh water migration of fresh from one habitat to another for feeding or spawning.
• Eg. Carps, catfish

3. Oceanodromous migration:

• It is the migration of fish within sea in search of suitable feeding and spawning ground.
• eg. Clupea, Thummus, Tuna

4. Latitudinal migration:

• it is the migration of fish from north to south and vice-versa.
• It is a climatic migration.
• Eg. Sward fish migrate north in spring and south in autumn.

5. Vertical migration:

• it is a daily migration of fish from deep to the surface and vice-versa for food, protection and spawning.
• Eg. Sward fish usually move vertically downward to greater depth for food.

6. Shoreward migration:

• it is the migration of fish from water to land. However it is a temporary migration.
• Eg. Eel migrate from one pond to another pond via moist meadow grass.

Significance of fish migration

• to find suitable feeding and spawning ground
• for protection from predators
• survive from extreme climatic conditions
• increases genetic diversity
• it is an adaptational characters for survival and existences

Migration in fishes

The post Migration in fishes appeared first on Online Biology Notes.

1. (Mollis or molluscs: soft)
2. Kingdom: Animalia
3. Habitat: Mostly aquatic and few are terrestrial
4. Body is soft without segmentation
5. Grade of organization: Organ system grade
6. Germ layer: Triploblastic
7. Symmetry: BIlaterally symmetry
8. The body is divided into head, muscular foot and visceral mass.
9. The body is covered by a mantle and a shell
10. Respiration: by gills (ctinidia) in the mantle cavity. lungs in terrestrial forms
11. Digestive system: Complete and developed
12. Circulatory system: Closed type
13. Heart consists of one or two auricle and one ventricle
14. Excretion: pair of Metanephridia (Kidney)
15. Nervous system: consists of three pair of ganglia (cerebral, visceral and pedal)
16. Sexes: Dioecious and few are hermaphrodite
17. Reproduction: gamatic fusion
18. Fertilization: external or internal
19. Development: direct or indirect by trochophore larvae.

Classification of Phylum Mollusca

There are six classes of which three are more prominent.

Class 1 Pelecypoda or Bivalvia

• Habitat: mostly marine
• They burrow in mud and sand.
• Symmetry: bilateral and the body is laterally compressed.
• No distinct head
• Examples: Mussels, Unio, Mytilus,

Class 2 Gastropoda

• Habitat: These are either aquatic or terrestrial
• They possess a spiral shell.
• The foot is large and flat.
• Head is well developed with tentacles and eyes.
• Examples: Hilex (Snail), Limax (Slug), Pila (Apple snail)

Class 3 Cephalopoda

• Habitat: mostly marine.
• They are adapted for swimming.
• The foot is modified into eight to ten long tentacles in the head region.
• The shell is either external, internal or absent.
• Examples: Octopus, Loligo, Sepia, spirula, Nautilus

Class 4 Monoplacophora

• Habitat: exclusively marine
• Head is present without eyes and tentacles
• Gills are external
• Excretion: by serially arranged nephridia
• Examples:

Class 5 Amphineura

• Habitat: mostly marine
• Body is elongated
• Eye and tentacles are absent
• Radula is present
• Examples; Chiton, Neomenia

Class 6 Scaphopoda

• Habitat: marine
• Body is bilateral symmetry elongated and enclosed in tusk shell
• Foot is reduced
• Excretion: a pair of Kidney
• Examples: Cadulus, Dentalium

Phylum Mollusca: General Characteristics and Classification

The post Phylum Mollusca: General Characteristics and Classification appeared first on Online Biology Notes.

1. (Echinos: Spines; derma: Skin)
2. Kingdom: Animalia
3. Habitat: These are exclusively marine
4. Grade of organization: organ system grade
5. Germ layer: triploblastic
6. Symmetry: Adults are radially symmetrical while the larvae are bilaterally symmetrical.
7. Coelom: present ( coelomate)
8. Body without segmentation
9. The shape of the body is flat, star like, spherical or elongated.
10. Head is absent
11. Presence of tube feet
12. Presence of water vascular system
13. Mouth is present on ventral side while anus is present on dorsal side
14. Respiration: by papule, gills or clocal respiratory tree
15. Nervous system: absent, they are brainless organism.
16. Circulatory system: is reduced, heart is absent
17. Blood has no pigment.
18. Digestive system: complete
19. Excretory system: absent
20. Sexes: mostly dioecious, rarely monocious
21. Reproduction:

• Sexual: by gamatic fusion
• Asexual: regeneration

1. Fertilization: external
2. Development: indirect with characteristic larvae

Classification of phylum Echinodermata

It is divided into 5 classes:

1. Asteroidea
2. Ophiuroidea
3. Echinoidea
4. Holothuroidea
5. Crinoidea

Class 1 Asteroidea

• Body is flattened star shaped with five arms
• They possesses tube feet with a sucker
• Presence of calcareous plates and movable spines.
• Respiratory organ: papulae
• Examples: Asterias (Star fish), Astropecten, Zoraster, Oreaster

Class 2 Ophiuroidea

• Body is flat with pentamerous disc
• They possess a long arm which is sharply demarcated from the central disc.
• They possesses tube feet without sucker
• Anus and intestine are absent
• Respiratory organ: Bursae
• Examples: Ophiderma, ophiothrix, Astrophyton, Amphuria, etc

Class 3 Echinoidea

• Body is disc-like hemi-spherical
• They are devoid of arms or free-rays.
• They possesses tube feet with a sucker.
• They possess compact skeleton and movable spines.
• Examples: Echinus (Sea urchin), Cidaris, Arbacia, Echinocardium. Diadema

Class 4 Holothuroidea

• Body is elongated in the oral-aboral axis and it is like cucumber.
• They have no arms, spines and pedicellariae.
• The tube feet are sucking type which is modified into tentacles and form a circle around mouth.
• Respiratory organ: cloacal respiratory tree
• Examples: Cucumaria (Sea cucumber), Holothuria, Mesothuria, etc

Class 5 Crinoidea

• Body is star shaped
• Some of the forms were extinct and living forms.
• Arms bifurcated, with two pinnules.
• They have tube feet without suckers
• Examples: Neometra, Antedon, Rhizocrinus, etc

Phylum Echinodermata: General Characteristics and Classification

The post Phylum Echinodermata General Characteristics and Classification appeared first on Online Biology Notes.

1. Arthros; Jointed, podos; Foot)
2. Kingdom: Animalia
3. Habitat: mostly terrestrial, also aquatic
4. Insects are the most successful life form on the planet: they make up more than half of all living things on Earth
5. Body has Three-part: head, thorax, abdomen.
6. Body is metamerically segmented
7. Three pairs of jointed legs (6 legs).
8. Compound eyes which contain several thousand lenses leading to a larger field of vision.
9. They possess two antenna.
10. Symmetry: bilateral
11. Germ layer: triploblastic
12. Grade of organization: organ system grade
13. Coelom: hoemocoel
14. Chitinous (hard) exoskeleton, no bones or a skeleton
15. Respiratory system: by general body surface, by gills, tracheae or book lungs
16. Circulatory system: open type with dorsal heart.
17. Excretion: malpighian tubules or green gland
18. Nervous system: dorsal brain with ventral nerve cord
19. Sexes are separate. Sexually dimorphism is present
20. Fertilization: internal.
21. Development: direct or indirect with larval stages.

Classification of Phylum Arthropoda

Arthropoda is classified into five classes on the basis of body divisions, body appendages, habitat, organs of respiration and modes of excretion.

Class 1 Crustacea

(Crusta: shell)

• Habitat: They are mostly aquatic, few are terrestrial and very few are parasitic.
• Cephalothorex: Head is often fused with thoracic segments to form cephalothorax.
• Thorax and abdomen have a pair of biramous appendages in each segment.
• Respiration: through the gills or general body surface.
• Excretory organs are modified coelomoducts which may either maxillary glands or antennary glands.
• Examples: Cancer (crab), Palaemon (Prawn), Daphnia (water flea) etc.

Class 2 Myriapoda

(Myrios: ten thousand; podos: foot)

• Habitat: Mostly terrestrial.
• Many appendages: Body is long with numerous segments each having one or two pairs of legs.
• Head is distinct with antennae, a pair of eyes and two to three pairs of jaws.
• Excretion: by malpighian tubules.
• Respiration: by trachea.
• Examples: Julus (Millipede), Scolopendra (Centipede), Spirobolus etc

Class 3 Insects

(Insectus: divided)

• Habitat: Mostly terrestrial and rarely aquatic
• Body divided into three regions: head, thorax and abdomen.
• Thorax has three segments, each bearing a pair of leg and a pair of wings found on second and third segments.
• Abdomen has 7-11 segments without appendages.
• Respiration: by tracheae, gills etc.
• Excretion: usually by malpighian tubules.
• Examples; Pieris (Butterfly), Periplaneta (Cockroach), Tabernus (Housefly), Mosquiotes, Ants, etc.

Class 4 Arachnida

(Arachne: spider)

• Habitat: mostly terrestrial and rarely aquatic
• Body is usually divided into cephalothorax and abdomen.
• There are four pairs of legs attached to the cephalothorax.
• Respiration: by tracheae or book lungs or gills.
• Excretion: by malpighian tubules or coxal gland or both.
• Examples: Aramea (Spider), Palamnaeus (Scorpion), Limulus (King Crab), etc

Class 5 Onychophora

(Onychos: claw; phoros: bearing)

• Habitat: mostly terrestrial
• Small sized arthropods
• Body is segmented
• Respiration: by tracheae.
• Excretion: by nephridia
• Examples: Paripatus

Phylum Arthropoda: General characteristics and Classification

The post Phylum Arthropoda: General characteristics and Classification appeared first on Online Biology Notes.

1. (Annelus: little ring)
2. Kingdom: Animalia
3. Habitat: mostly aquatic, some are terrestrial
4. Habit: free living
5. Symmetry: bilateral symmetry
6. Coelom: coelomate (Body cavity is a true coelom, often divided by internal septa)
7. Body is metamerically segmented
8. Grade of organization: organ system grade
9. Germ layer: triploblastic
10. Body possesses 3 separate sections, a prosomium, a trunk and a pygidium.
11. Digestive system: complete and developed
12. Respiration: by general body surface
13. Nervous system: nervous system with an anterior nerve ring, ganglia and a ventral nerve chord.
14. Circulatory system: Has a true closed circulatory system.
15. Excretion: by nephridia
16. Reproduction: Sexual and gonochoristic or hermaphoditic.
17. Fertilization: Internal or external
18. Development: direct with no larval stages

Classification of Phylum Annelida

Phylum Annelida is divided into four main classes, primarly on the basis of setae, parapodia, metameres and other morphological features.

Class 1 Polychaeta

(Polys: many; chaite:hair)

• Habitat: They are marine, terrestrial, and freshwater.
• Archetypical protosome development (schizocoely).
• True coelomates (schizocoelomates).
• Bilaterally symmetry, segmented worms.
• Complete digestive system.
• Closed circulatory system.
• Well-developed nervous system.
• Excretory system: Both metanephridia and protonephridia.
• Lateral epidermal setae with each segment.
• Dioecious or hermaphroditic.
• Fertilization: external
• Examples: Nereis (sandworm), Syllis, Sabella

Class 2 Oligochaeta

(Oligos: few, chaite: hair)

• Habitat: mostly terrestrial and few are freshwater
• Body metamerically segmented
• Clitellum present
• Hermaphrodite but cross fertilization occur
• Fertilization: external
• Cocoon formation occur
• Examples: Pheretima posthuma (Earthworm), Lumbricus, Stlaria, Tubifex

Class 3 Hiradinea

(Hirudo: leech)

• Habitat: primarily freshwater annelids but some are marine, terrestrial and parasitic
• The body has definite number or segments.
• The tentacles, parapodia and setae are totally absent.
• They are hermaphrodite.
• Fertilization: internal and a larval stage is absent.
• Examples: .Hirudinaria (Leech)

Class 4 Archiannelida

(Arch; first)

• Habitat: They are strictly marine.
• The body is long and worm like.
• The setae and parapodia normally absent.
• They may be unisexual or hermaphrodite.
• The development: indirect forming trochophore larva.
• Examples: .Protodrillus. Dinophilus, Protodrilus

Phylum Annelida: General Characteristics and Classification

The post Phylum Annelida: General Characteristics and Classification appeared first on Online Biology Notes.