PICTORIAL EXPLAINATION.

1. SCIENCE
ASSIGNMENT
BIOLOGY PART
BY JEET DUTTA
PHONE NO. 8811839838, SCHOOL VKV BOKULONI,
DIBRUGARH ASSAM, EMAIL – jeetdutta000@gmail.com

2. Phylum 11. Chordata
Chorda the Greek word which means ‘string’. Chordata are
characterized by the following three ways:
(a) A dorsal, hollow, tubular nerve cord;
(b) A pliable rod called notochord that occur ventral to nerve cord and is
replaced by a bone to form a vertebral column in vertebrates;
(c) Paired gill-slits in the pharynx.
These three characters are always present at some stage in development
or throughout a life time.

3. The notochord (Gr. Noton = back + L.chord = cord) is a long rod-like support
structure that runs along the back of an animal and separates the nervous tissue
from the gut. It provides a space for muscules to attach for ease of movement.
Characteristics of Chordata-
1. Body bilaterally symmetrically , metamerical segmented, triploblastic and
coelomate.
2. A post-anal tail present at some stage of life.
3. Segmental muscles in an unsegmented trunk.
4. Ventral heart, with dorsal and ventral blood vessels and closed blood vascular
system.
5. Complete digestive system.
6. A cartilaginous or bone endoskeleton present in majority of members.

4. Chordata is the most advanced group of animals. Phylum Chordata is
divided into two groups , viz., Protochordata and Vertebrata.
Protochordates may not have a proper notochord present during all
stages of their lives. Protochordata includes two subphyla,
Urochordata and Cephalochordata. Group vertebrata is divided into
subphyla, viz ., Agnatha and Gnathostomata. Agnatha includes a
single class Cyclostomata , while Gnathostomata is divided into six
classes :Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves
and Mammalia. Chondrichthyes and Osteichthyes, both are
commonly known as fishes.

5. A. Protochordata
Subphylum 1. Urochordata-
 They are bag like, sessile, soft bodied, non metameric animals.
 Adult body is covered with a tunic or test containing cellulose.
 Dorsal tubular nerve cord is present in the larval form and it degenerates in the form
of small ganglion in the adult.
 The only chordate character present in the adult animal is the presence of numerous
gill-slits in the pharynx.
 Hermaphrodites and exclusive marine, solitary and colonial.
Examples: salpa, doliolum, herdmania etc.

6. Subphylum 2.Cephalochordata (Gr., kephale-head)
 Fish-like, metamerically segmented, headless coelomate animals which
retain notochord, dorsal tubular nerve cord and pharyngeal gills-slits
throughout life .
 Notochord and nerve cord (without a distinct brain) extend throughout the
entire length of the body.
 Exoskeleton , head, jaws and paired fins are absent.
 Pharynx large and perforated by numerous gill-slits.
 Sexes separate and marine , burrow in the sand of shallow sea water.
Example: Amphioxus

7. B. Vertebrata
Subphylum 1. Agnatha (Gr., a- without ; gnathos- jaws)
 Animals have vertebral column and cranium. They are the most primitive
vertebrates known to humans.
 Without true jaws and paired appendages or fins.
Agnatha includes the following single class :
Class Cyclostomata (Gr., kyklos- circle, stomata- mouth)
 Body is long, elongated and eel-like.
 Skin is soft , slimy, smooth and scale less.
 Mouth is round, heart is two chambered and single nostril is present.
 Free living and ectoparasites of fishes.
Example: Petromyzon(lamprey), Myxine (hagfish).

8. Subphylum 2. Gnathostomata (Gr., gnathos-jaws ; stomata-
mouth)
 Vertebrates with jaws and paired appendages.
 This subphylum is divided into the following six classes :
Class 1. Chondrichthyes
Class 2. Osteichthyes
Class 3. Amphibia
Class 4. Reptilia
Class 5. Aves
Class 6. Mammalia

9. Class 1. Chondrichthyes
 Marine fishes with completely cartilaginous endoskeleton. They are
generally large in size (up to 10-20 metres long).
 Streamlined body is either laterally compressed and spindle shaped or
dorsoventrally flattened and disk shaped.
 Mouth is ventral in position and skin is tough and covered with minute
placoid scales.
 Heart is two chambered.
 Digestive system has a J-shaped stomach and intestine has spiral
valves.
 Sense of smell, vibration reception are well developed.
Example : Scoliodon (dog-fish, Indian shark)

10. Class 2. Osteichthyes
 Marine and fresh-water fishes with partly or whole bony endoskeleton and
the size varies from 10mm to 4metres.
 Body is generally spindle-shaped and skin is either naked or covered with
cycloid or ctenoid scales.
 Mouth is usually terminal (anterior) in position, four pairs of gills are present
and they are covered by operculum.
 Heart is two chambered and they are cold-blooded animals which lay eggs
and fertilization is external.
 Excrete ammonia.
Example : Labeo (rohu, carp) Hippocampus (sea horse)

11. Class 3. Amphibia
 It includes frogs, toads, newts and salamanders.
 In evolutionary terms amphibians from the first group among the
chordates to live outside water and comprise of first four-legged
land vertebrates. They live on land but lay their eggs in water.
 Skin is smooth or rough , moist, slimy, glandular and mostly without
scales and the mouth is usually large.
 It has three chambered heart and respiration is done by gills , lungs
skin or the mouth lining.
 It excrete either ammonia or urea and the animals are
ectothermal(cold blooded animals).
Example : Rana(bull frog), Bufo (toad)

12. Class 4. Reptilia
 Ectothermic, terrestrial or aquatic vertebrates with a body covered with dry
water-proof skin having horny epidermal scales.
 Body varies in form and is usually divided into head, neck, trunk and tail.
 Respiration is through lungs only and fertilization is internal.
 Heart is three chambered and is divided into two auricles and an
incompletely divided ventricle.
 Terrestrial reptiles such as snake and lizard excrete uric acid.
 Most reptiles are oviparous and lay egg, a few are viviparous (lizard and
snake).
Example : Chamaeleon, Crocodilus.

13. Class 5. Aves
 Warm-blooded, tetrapodous vertebrates (birds) with various flight adaptations.
 Size ranges from smallest humming bird to largest ostrich.
 Four-chambered heart and they breath through lungs.
 Spindle shaped body is divisible into head, neck, trunk and tail.
 Hind limbs bear four clawed digits and are adapted for walking.
 Excrete semisolid urine having uric acid and are oviparous.
 Birds have highly developed voice, hearing and vision. They also have specialised
sense for nest building and care for the young.
 Fertilization is internal.
Example : White stork

14. Class 6. Mammalia
 Mammals are warm-blooded and the most evolved animals of Animal
Kingdom.
 Hairs and the subcutaneous fat form an insulating layer.Cutaneous
glands such as sweet glands, scent glands are present.
 Body is divisible into head, neck, trunk and tail.
 Females have milk-producing mammary glands which secrete milk for the
nourishment of the young.
 Respiration is through lungs only and heart is four-chambered.
 Excrete urea and fertilisation is internal.
 Mammals are primarily terrestrial animals.
Example : Bat, Homo (human being)