The word Chondrichthyes is formed from the Greek word chondros meaning cartilage and ichthys meaning fish. Cartilaginous fishes belong to the class Chondrichthyes. They are marine and carnivorous animals. Their number of species is 1,207.
Characteristics of Chondrichthys
1. Their body is flat or mace-shaped. They are jawed animals.
2. Their endoskeleton is made of cartilage.
3. Their body skin is hard and tough.
4. Body covered by placoid scales.
5. There are 5-7 pairs of gill slits on both sides of the head.
6. They do not have horns.
7. The mouth and nostrils are located at the base of the digit. There are numerous rows of placoid teeth in the jaws. Siddiq Publications
8. The body does not have air sacs or sacs.
9. The digestive system consists of a J-shaped stomach, a spiral-shaped intestine, and a fatty liver.
10. Their heart is two-chambered and known as the venus heart.
11. Caudal fin heterocercal type. That is, the caudal fin is divided into two unequal parts.
12. In male fish the pelvic fins are modified to form copulatory organ clusters.
13. They are unisexual animals. Fertilization occurs. Direct exposure. They are ovaries, ovaries or uterus. Dr. Siddiq Publications
Some animals of the Chondrichthyes
Shark- Scoliodon sorrakowah
Thutree shark- Scoliodon laticaudus
Hammerhead shark- Eusphyra blochii
Saw fish – Pristis pectinata
Ratfish- Hydrologus collei
Guitar fish – Rhinobatos rhinobatos
Raja – Raja raja
Sting Ray – Plesiobatis daviesi
Electric fish – Torpedo torpedo
White skates- Rostroraja alba
.
Placoid scale
Microscopic scales present in the skin of cartilaginous fish are called placoid scales. It is a triangular plate formed from the skin. It has three sharp spines. For example – Scoliodon laticaudus. Dr. Siddiq Publications
Heterocercal
If the caudal fin segments of fish are not equal then it is called heterocercal. Chondrichthys fishes have heterocercles. For example, Scoliodon laticaudus.
Dog fish
The fish whose mouth is shaped like a dog’s mouth are called dog fish or dog fish. Their jaws have sharp teeth. Dogfish belong to the Chondrichthyes class. For example – Scoliodon laticaudus. Dr. Siddiq Publications
Sow fish
Those fishes which have a long tip like a saw at the front of their body are called saw fish or saw fish. They belong to the Chondrichthyes class. For example – Pristis pectinata.
Actinopterygii, Osteichthyes
The word Actinopterygii is formed from the Greek word actis meaning rays, pteryx meaning fin. Actinopterygii means ray-finned. Ray-finned fishes are known as Actinopterygii. About 96% of living fish belong to this category. They are 10 mm to 4 m long and weigh 1500 kg. Their number of species is 31,045. 12 classes, 48 tribes and 253 species of this class have been identified in the fresh water of Bangladesh.
Characteristics of Actinopterygii
1. Their endoskeleton is made up of bones.
2. Body covered with cycloid, tinoid and ganoid scales. Some fish do not have scales. Such as- horn, Magur etc. Dr. Siddiq Publications
3. All body fins are bony and have dermal rays (lepidotrachea).
4. Their gills are covered with kanko.
5. Caudal fin homocircular type. That is, the tail fin is divided into two equal parts.
6. Their mouth is located at the tip.
7. Their brain consists of cerebellum, optic lobe and cerebrum.
8. There are 10 pairs of carotid nerves in the body.
9. The reproductive organs consist of four pairs of gills. On both sides of the head, there is a flower opening. Dr. Siddiq Publications
10. Air sacs are present in the body.
11. They breathe and float with the help of crackers.
12. Their heart is two-chambered and known as the venus heart.
13. They are unisexual animals. Excretion occurs. Direct and indirect effusion is observed.
[key words to remember features: endoskeleton, cycloid, tenoid, ganoid, cutaneous ray, conch, homocercal, pore, brain, carotid nerve, gill, air sac, heart]
Some fishes of the class Actinopterygii
Ilisha- Tenualosa ilisha
Roe – Labeo rohita
Catla- Catla catla
Taki fish – Channa punctatus
Magur fish – Clarias batrachus
Boal- Wallago attu
Queen fish – Botia dario
Tuna fish – Thunnus albacares
Where fish- Anabas testudineus
Chital fish- Notopterus chitala
Pangasius fish – Pangasius pangasius
Cirrhinus cirrhosus
Bombay Dak/Lytra fish- Harpadon nehereus
Sturgeon fish – Acipenser oxyrhynchus
Paddle fish – Polyodon spathula
Horn fish – Heteropneustis fossilis
Sunfish – Mola mola
Cat fish
Those fishes that have barbs around their mouth like cat’s whiskers are called cat fish. Catfish belong to the class Actinopterygii. For example, horn fish, magur fish etc. Dr. Siddiq Publications
Homocercal
If two segments of the caudal fin of a fish are equal, it is called homocircular. Fishes of the class Actinoterygii have homocercles. For example – Ilisha (Tenualosa ilisha).
Cycloid scale
Fish scales that are round or oval, with growth lines and smooth edges are called cycloid scales. The inner part of the rib is called the anterior part, the outer part is called the posterior part and the two side parts are called the lateral parts. The tip has longitudinal grooves or radii. For example – Labeo rohita. Dr. Siddiq Publications
Cteoid scale
The cartilage in bony fish is called tinoid cartilage. Its posterior margin is finely barbed. For example – Anabas testudineus.
Sarcopterygii
The word Sarcopterygii is derived from the Greek words sarkos meaning flesh and pteryx meaning fin. Pindaca finned fishes belong to the class Sarcopterygiae. Their paired fins are fleshy hence they are known as lobe finned. They are known as lungfish and coelacanth. Lungfish are widespread in Africa, South America and Australia. Coelacanths are widespread along the coast of the Indian Ocean and Indonesia. Scientists believe that from this class of fish, amphibians emerged as quadrupeds and terrestrials. There are currently 8 species of fish alive.
Characteristics of Sarcopterygiae
1. The endoskeleton is made up of endochondral bone.
2. Body covered with ganoid or cosmed scales. Cosmead starch contains cosmin.
3. Pinds have paired fins with fleshy lobes.
4. The caudal fin is diphysercal in nature. That is, the two parts of the caudal fin are united and are located around the tail as a uniform and flexible fin.
5. Bony gills are present on both sides of the head. They breathe through gills.
6. Their gills are covered by gills.
7. Their air sacs or patacas are rich in blood vessels and help them to swim and float.
8. Their heart has two chambers.
9. They are cold blooded or ectothermic animals. That is, their body temperature changes with the rise and fall of the environment temperature.
10. Their jaws have enamel covered teeth.
11. They are unisexual animals. They are external or internal.
[key words to remember features: endoskeleton, ganoid, cosmed, fin, diphycercal, gill, kanko, cracker, ectothermic, enamel]
Sarcopterygia bear evidence of evolution
1. Their endoskeleton is made up of bones. Therefore, the body structure is developed.
2. Body covered with ganoid or cosmed scales. It acts as an exoskeleton.
3. The body consists of paired fins with fleshy segments which are suitable for locomotion.
4. Their caudal fins are diphycircal in nature. It acts as a locomotor organ.
5. They have jaw teeth. Teeth are covered by enamel
6. There are air sacs in the body. It holds air and helps the fish float and breathe.
7. They are unisexual and occur either externally or internally
Some fishes of the class Sarcopterygiae
Coelacanth – Latimeria chalumnae
Australian Long Fish – Neoceratodus forsteri
African Long Fish – Protopterus onnectens
South American Lungfish – Lepidosiren paradoxa
Lung fish
Those fishes whose air sacs have been converted into lungs are called lung fish. Lungfish belong to the class Sarcopterygiae. For example – Neoceratodus forsteri.
Ganoid scale
In bony fishes, rhomboid-shaped scales are called ganoid scales. It is also called Cosmed Aish. It is composed of cosmine. It is covered by enamel called ganyon.
Diphycercal
When two segments of the caudal fin of a fish are united to form a uniform and flexible fin, it is called diphyserical. Fishes of the class Sarcopterygiae have diphycercles. Eg – Latimeria chalumnae
Fish
Cold-blooded aquatic vertebrates that carry out respiration with the help of gills and move with the help of fins are called fish. The classes Myxini, Cephalospidomorpha, Chond
Amphibia
The word Amphibia is formed from the Greek word amphi meaning both and bios meaning life. Animals of this class were the first to conquer land. They are known as amphibians because they live in water and on land. There are currently 7,700 living amphibian species. Among them 715 species of amphibians with tails, 200 species of amphibians without legs and 6,785 species of amphibians with four legs. 2 classes, 4 tribes, 47 frogs and 2 Sicilian amphibians have been identified in Bangladesh.
Characteristics of amphibians
1. Body skin glabrous, glandular, non-scaly, smooth and moist.
2. Respiration is by gills in the larval stage and by lungs in the adult stage.
3. There are 4 clawless toes on the forefoot and 5 on the hindfoot.
4. They are cold-blooded ectothermic animals. That is, their body temperature changes with the rise and fall of the environment temperature.
5. The first stage of life lives in water and the adult stage lives on land. That is, they live a double life.
6. The heart has three chambers. The heart consists of two atria, one ventricle, one sinus venosus and one conus arteriosus.
7. Renal and hepatic portal systems are advanced.
8. Their body is divided into head, neck and trunk.
9. The crown of the head is connected to the spinal cord by two occipital condyles.
10. The nervous system is divided into three parts. Central, peripheral and automated. There are 10 pairs of carotid nerves.
11. They are unisexual animals. They are excreted.
12. Their life cycle includes the tadpole larval stage.
[key words to remember features: skin, gills, lungs, fingers, ectothermic, bivalve, heart, hepatic portal system, occipital condyle, nervous system, tadpole]
Amphibians bear evidence of evolution
1. The skin is glabrous, glandular, moist and non-scaly which is conducive to both aquatic and terrestrial environments.
2. Respires by gills and complete lungs in the larval stage. Therefore the first stage of life can easily live in water and the full stage in water.
3. Contains paired carotid nerves that transport impulses.
4. The heart has three chambers, two atria and one ventricle. In the process of evolution, Nilaya bifurcation will be divided into four chambers.
5. The eye has three lobes. It protects the eyes.
6. 4 fingers on the front foot and 5 on the back foot. Movement is easy because of fingers.
7. Cold-blooded or ectothermic animals. When the heart becomes four-chambered, they become hyper-blooded or endothermic animals.
8. The life cycle of the tadpole consists of lava stages. The first stage lives in water and the adult stage lives on land. That is, living a double life.
Some animals of class Amphibia
Kuno frog – Duttaphrynus melanostictus
Ghecho frog – Chiromantis simus
Hyla chinensis
Golden frog – Rana tigrina
Flying frog – Rhacophorus reinwardtii
Golden Frog – Phyllobates terribilis
Salamander – Salamandra maculosa
Red salamander – Pseudotriton ruber
Ceylon Sicilian – Ichthyophi sglutinosus
Crested Newt – Triturus cristatus
Siren – Siren lacertina
Necturus – Necturus maculosus
Tuatara – Sphenodon guntheri
Chameleon – Chamaeleo chamaeleon
Reptilia
The class Reptilia is named after the Greek word rep meaning chest walking. Reptilia means reptiles. They walk with their chest full. The Mesozoic era of 16 and a half million years ago is called the Age of Reptiles. Their number of species is 9,831. 3 classes, 25 tribes and 167 species have been identified in Bangladesh.
Features of Reptilia
1. The body is dry and composed of scales or hard plates arising from the epidermis.
2. Each foot has 5 clawed toes.
3. Their body is divided into three parts. Head, neck and body.
4. The ventricles of their heart are incompletely bifurcated (except in crocodiles).
5. They are ectothermic land animals. That is, their body temperature changes with the rise and fall of the environment temperature. Siddique Publications
6. They are cold blooded animals. So it goes into hibernation in winter.
7. They walk on the chest.
8. Their number of carotid nerves is 12 pairs or 24.
9. They lay eggs. ie Oviporous. Eggs are covered with a leathery calcareous shell. Siddique Publications
10. The crown of the head is connected to the spinal cord by an occipital condyle.
11. Retractable holes are located transversely.
12. Four extra-embryonic membranes (amnion, chorion, yolk sac, allantois) are formed during the development of the embryo. Siddique Publications
13. They are unisexual animals. Fertilization occurs. Muscular male sexual organs exist. Dr. Siddique Publications
14. They have no larval stage.
[key words to remember characteristics: epidermis, hard plate, finger, heart, ectothermic, hibernation, thoracic mass, cranial nerve, ovipore, occipital condyle, excretory pore, copulatory organ, larva]
Some animals of the class Reptilia
Lizard- Hemidactylus frenatus
Flying lizard – Chameleon vulgaris
Tortoise – Trionyx gangeticus
Sea turtle – Caretta caretta
Takshak – Gekko gecko
Gharial – Gavialis gangeticus
Gokhra snake – Naja naja
Guisap – Varanus komodoensis
Chameleon – Calotes versicolor
Crocodile – Crocodylus porosus
Fresh water crocodile – Crocodylus palustris
Aves
The Latin word Avis means bird. Vertebrate animals that have left water and land to take to the skies are called birds. Their bodies are adapted for flight and they have evolved as flying machines. The physical characteristics of the birds resemble those of archosaurs of the Mesozoic era. The total number of species is 10,000. 21 classes and 706 species of Avis class have been identified in Bangladesh. Dr. Siddique Publications
Features of Avis
1. The body is covered with feathers and the forelegs are modified into two wings.
2. Their necks are elongated and S-shaped.
3. The jaws are toothless and have evolved into beaks.
4. Intraskeletal pores, bone hard, light and airy. Bones contain air-filled cavities.
5. Air sacs exist in the lungs. The sphincter consists of the syrinx, the organ that produces sound.
6. They are endothermic or warm-blooded animals. That is, their body temperature does not change with the rise and fall of the environment temperature.
7. The heart has four chambers, 2 atria and 2 ventricles.
8. Their digestive system consists of crop and gizzard. So able to digest energy food quickly. Dr. Siddique Publications
9. The crown of the head is connected to the spinal cord by an occipital condyle. The sternum forms a boat-like keel.
10. They are bipedal and can fly.
11. Their feet have clawed toes.
12. They lay eggs. The egg hatches and the baby comes out.
13. Newborn babies are active and vigorous or naked and weak.
[key words to remember characteristics: feather, wing, neck, beak, air cavity, air sac, syrinx, endothermic, heart, digestive system, occipital condyle, keel, biped, toe, egg] Dr. Siddique Publications
Adaptation for successful flight adaptation
1. Their bodies are covered with feathers. The body is light and the feathers help to float in the air. Siddique Publications
2. Their necks are elongated and S-shaped. So can lean forward easily.
3. They are bipedal animals. The forelimbs have evolved into wings. Wings are their main flight organ. Dr. Siddique Publications
4. Jaws have evolved into beaks. It helps in flight.
5. Their bones are hard, light and airy. It reduces body weight and can fly easily. Dr. Siddique Publications
6. They have air sacs in their lungs. Air sacs contain air. The body is light and can fly easily.
7. The heart has four chambers, 2 atria and 2 ventricles. So pure blood supply is ensured. Dr. Siddique Publications
8. The sternum has formed a boat-like keel which aids in flight
Birds are called majestic reptiles
Birds evolved from reptiles during the Mesozoic Era. The ancestors of birds are reptiles. Reptiles have evolved into birds. In the early 20th century, the famous ornithologist Thomas Huxley called them birds as the majestic reptiles. Archeopteryx is a fossil link between reptiles and birds. That is, archeopteryx evolved from reptiles and birds evolved from archeopteryx. The characteristics of the creation of birds from reptiles are-
1. Reptiles are cold-blooded animals with low metabolic rates. Birds are high-blooded animals with high metabolic rate. Dr. Siddique Publications
2. Reptiles are mobile animals. Birds can move faster due to the gain in flight ability. Siddique Publications
3. Reptiles have dry fibrous bodies. Bird feathers have been created from the dung of reptiles. Dr. Siddique Publications
4. The four-chambered heart of a bird has been created from the incomplete four-chambered heart of a reptile. Siddique Publications
5. There are two systemic arches in the circulatory system of reptiles and one systemic arch of birds. Siddique Publications
6. The renal portal system of reptiles is highly developed. It is decaying in birds.
7. The jaws of reptiles gave rise to the long beaks of birds.
The above discussion proves that birds have evolved from reptiles. That is, birds are majestic reptiles.
Some birds of the class Avis
Doyle – Copsychus saularis
Rooster – Galus galus
Owl – Bubo bubo
Eagle – Haliacetus leucogaster
Pigeon – Columba livia
Hummingbird – Mellisuga helenae
Dove – Streptopelia decaocto
Shalik – Lamprotornis hildebrandti
Cuckoo – Eudynamys scolopaceus
Buck – Nycticorax nycticorax
Passer domesticus
King vulture – Sarcogyps calvus
Black Pheasant – Francolinus francolinus
Quail – Coturnix coturnix
Moina – Gracula Religiosa
Tia – Psittacula krameri
Dahuk – Amaurornis phoenicurus
Crane – Grus antigone
Crow – Corvus splendens
Bulbul – Pycnonotus cafer
Ostrich – Struthio camelus
Peacock – Pavo cristatus
Babui bird – Ploceus philippinus
Pelican – Pelecanus philippensis
Mammalia
Mammalia is named after the Latin word Mamma. The word Mammalia means mammals. They can range from the tiny Thai bat (1.5 grams) to the largest blue whale (130 metric tons). They have taken over the world. Humans are the greatest animals on earth. Their number of species is 6,000. 10 classes, 35 tribes and 138 species of mammals have been identified in Bangladesh. Dr. Siddique Publications
Characteristics of mammals
1. Their skin is covered with hair.
2. The outer ear is attached to the pinna. The middle ear consists of malleus, incus and stapes. Cochlea exists in the inner ear. Dr. Siddique Publications
3. Mature females have active mammary glands. Cubs drink mother’s milk.
4. Between the thorax and abdomen is a membrane called the diaphragm.
5. The crown of the head is connected to the spinal cord by two occipital condyles.
6. They have sweat glands and scent glands.
7. They are endothermic or warm-blooded animals. That is, their body temperature does not change with the rise and fall of the environment temperature. Siddique Publications
8. Their red blood cells are without nucleus (exception – camel).
9. Their brains are developed and they have all the tantras.
10. They have 12 pairs or 24 cranial nerves.
11. They have teeth in both jaws.
12. The heart has four chambers. Two atria and two ventricles.
13. The circulatory system is advanced. Bi-cycle or double circulation. Systemic and pulmonary cycles are seen.
14. They have vocal cords in their larynxes. The glottis has a covering called the epiglottis.
15. Their poison is internal. They bear the uterus and give birth to babies.
[key words to remember features: hair, pinna, cochlea, cochlea, mammary gland, diaphragm, sweat gland, olfactory gland, endothermic, red blood cell, cranial nerve, tooth, heart, circulatory system, vocal card, uterus] Dr. Siddique Publications
Some animals of the class Mammalia
Human – Homo sapiens
Tiger – Panthera tigris
Lion – Panthera leo
Deer – Axis axis
Guinea pig- Cavia porcellus
Rabbit – Sylvilagus audubonii
Dolphin – Delphinus capensis
Bat- Pteropus giganteus
Kangaroo – Macropus giganteus
Platypus- Ornithorhynchus anatinus
Squirrel- Funambulus palmarium
Camels – Camelus dromedaries
Rhesus monkey- Macana mulatta
Cow – Bos indicus
Goat- Capra hircus
Sheep – Ovis aries
Buffalo – Bubalus bubalis
Hanuman- Trachypithecus phayrei
Rat- Bandicota indica
Dog – Canis lupus familiaris
Cat- Felis catus
Guinea pig- Cavia porcellus
Pig – Sus scrofa
Water elephant- Hippopotamus amphibius
Gorilla – Gorilla gorilla
Fox – Canis aureus
Elephant – Elephas maximus
Rhinoceros – Rhinoceros unicomis
Bear- Melarsus ursinus
Giraffe – Giraffa camelopardalis
Whales – Balaenoptera musculus
Classification of mammals
Class Mammalia is divided into three subclasses based on the nature of reproduction. These are Prototheria, Metatheria and Eutheria.
1. Prototheria: The word Prototheria is formed from the Greek word protos meaning first and ther meaning mammal. Mammals that lay eggs are called ovipositors or prototheria. They live in Australia and New Guinea. Dr. Siddique Publications
(i) They are primitive egg-laying mammals. They are not immortal.
(ii) They lay eggs with a leathery covering. A newborn is born from an egg.
(iii) Newborns suck the mother’s milk. Because their mammary glands do not have nipples.
(iv) They have sharp lips, no teeth and no external ears.
(v) There is only one mucous membrane for excretory, reproductive and digestive system. Hence they are called monotrims.
Examples: Goose-billed Platypus (Ornithorhynchus anatinus), Short-billed Echidna (Tachyglossus aculeatus)
2. Metatheria: The word Metatheria is formed from the Greek word meta meaning medium and ther meaning mammal. Mammals that have a pouch called a marsupium are called marsupials or metatheria. They live in Australia, Tasmania, New Guinea, Central and South America.
(i) They are simple immortal mammals.
(ii) They give birth to very immature neonates.
(iii) Female animals have pouch called marsupium. In this pouch the new-born attain fullness. Hence they are called marsupials.
(iv) Mammary glands including nipples are exposed in marsupium.
(v) They have two uteri and two vaginas.
Examples: Red kangaroo (Osphranter rufus/Macropus rufus), Virginia opossum (Didelphis virginiana), Koala (Phascolarctos cinereus).
3. Eutheria: The word Eutheria is formed from the Greek word eu meaning nature and ther meaning mammal. Mammals that possess true immortality are called immortalized mammals or eutheria. They are spread throughout the world. Dr. Siddique Publications
(i) They are true immortal mammals. Their embryo consists of chorion and allantois.
(ii) Immortals provide nutrients during their flowering. The gestation period is long lasting.
(iii) Their embryos remain in the uterus for some time and give birth to mature neonates.
(iv) Mammary glands of female animals are highly developed. It contains nipples.
(v) Their vagina is one. The testes are located in the scrotal sac.
Example: Human (Homo sapiens), Shushuk (Platanista gangetica), mouse (Mus musculus), Rusa deer (Rusa unicolor), tiger (Panthera tigris), fruit bat (Pteropus giganteus). Siddique Publications
Diaphragm
The muscular membrane between the thoracic and abdominal cavities of mammals