B. Sc. Biotechnology (IISemester)
Examination, 2013 Zoology III
LBZS 203: CHORDATE
Time Allowed: Three hours
Maximum Marks: 30
Multiple choice Answer: All are compulsory
10x1=10
Ans 1. (i) c
(ii) d
(iii) c
(iv) b
(v) a
(vi) a
(vii) a
(viii) b
(ix) a
(x)c
5x4=20
Ans 2. Affinities of Urochordata in details
Affinities with nonchordates
In sorne features, urochordates show some similarities with certain nonchordate groups.
(i) Porifera, Coelenterata and urochordates are sessile in nature.
(ii) Mechanism of filter feeding and respiration through a water current is parallel with
that of sponges, molluscs (oysters) and lophoPhorates.
(iii) Budding chain of new zooids is common with coelenterates and annelids.
(iv) Larval eyes and otocysts are found in many invertebrates.
(v) Colonial mode of life of simple and composite fixed ascidians is observed in a
number of invertebrates,
(vi) Presence of typhlosole in intestine.
None of the above features establishes any nonchordate relationship. These similarities
are only due to similar mode of life and parallel evolution.
Affinities with chordates
The ascidian tadpole larva possesses all the basic chordate
Characters such as : (i) rod-like notochord forming axial skeleton of tail, (ii) dorsal
tubular nerve cord, and (iii) gill-slits in the plaryngeal wall. This is probably because both
urochordates and the other chordates have originated from a common ancestor,
Affinities with Hemichordata.
The assumption that nearest relatives of urochordates are the exisiting hemichordates, is
based on the following similarities :
(l) Same structural plan of pharynx perforated by gill-slits and having similar accessories.
Similar development of central part of nervous system.Occurrence of restricted
notochord.
Objections. However, the two groups have important differences.
(i) Balanogtossus lives in burrows, but urochordates may be fixed, inert or
pelagic. (ii) Hemichordate body is divisible into proboscis, collar and trunk which is not
found in urochordates.(iii) A true.notochord is present in the tail ofascidian.larva,whereas
the buccal diverticulum of Bahnoglossus is no longer considered a notochord. Thus, even
inclusion of hemichordates as tnre chordates has become doubtful so that they are
considered nowadays as an independent nonchordate phylum. The similarities of both the
groups are probably because of their remote phylogenetic relationship with the ancestral
common stock.
Affinities with Cephalochordata. The adult urochordate bears the following structural
similarities with Branchiostoma :
(i) Similar ciliary filter feeding or food concentration mechanism and respiratory
mechanism.
(ii) Large pharynx with similar accessories.
(iii) Branchial tentacles ate similar to velar tentacles.
(iv) Similar endostylea nd associatedp arts,,
(v) Similar atrial complex.
Besides the fundamental three chordate characteristics (notochord, dorsal tubular nerve
cord and pharyngeagl ill-slits), the ascidian tadpole larva and Branchiostoma also share
the following similarities :
(i) Identical early stages of development.
(ii) Tail with median vertical fins without fin rays.
(iii) Median sensory organs (otocyst, ocellus, statocyst).
(iv) Pharynx with endostyle.
(v) Atrial complex similar.
Objections. However two groups have differences and their resemblances point out to a
probably remote common ancestry. Their differences demand their taxonomic
arrangement in two separate subphyla under the phylum Chordata.
Affinities with Vertebrata. The ascidian tadpole larva can be compared with a larval
fish. It resembles higher chordates in having (i) dorsal tubular nerve cord, (ii) axial
skeletal notochord, (iii) pharyngeal gill- slits, (iv) postanal tail covered by vertical caudal
fin. (v) Type of cleavage and gastrulation. In the adult ascidian (i) neural gland is
homologous with vertebrate pituitary(ii) endostyle with vertbrate thyroid (iii) typhlosole
comparable to intestinal spiral valve of elasmobranch fishes.
Conclusion: From above discussion it is obvious that urochordates are primitive and
degenerate descendants and ancestral chordates. The tadpole larva represents the relic of
a free swimming ancestral chordate.
Ans (3)
Ans (4)
Parental care means care of the eggs or juveniles till they reach the reproductive age.
Parental care evolved to reduce the energy expenditure on reproduction, as in the absence
of it animals must produce millions of eggs so that few could survive to replace the
parents to ensure existence of the species. Lower animals produce excessively large
number of eggs and do not exhibit parental care but higher animals such as vertebrates,
show varied degree of parental care in order to reduce the energy expenditure in
reproduction. Terrestrial environment being much harsher than the aquatic one,
amphibians were the first vertebrates to have evolved different kinds of parental care to
protect their young .
(i) Protection by nest ,nurseries or shelters
Selection of site: Many amphibians lay egg in protected, moist microhabits on land.
Many tree frogs and toad lay their eggs not on land but on leaves and branches
overhanging water. Species of Phyllomedusa, Rhachophorus, Hylodes etc glue their eggs
to foliage hanging over water. Rhacophorus malabaricus in India and Chiromantis of
Africa also deposit their spawn on trees. Many tree frogs deposit eggs in water that
accumulates in epiphytic tropical plants.The tadepoles on hatching drop into water
beneath to complete their metamorphosis.
Foam nests: Many amphibians convert copious mucous secretion into nests for their
young . In the Japanese tree frog, Rhacophorous schlegeli, the mating couple digs a hole
or tunnel into which eggs are left in a frothy mass to avoid desiccation. During rains,
hatching tadpoles are washed washed down the slopping tunnel into pond or river water
for further development. The female of South American tree frog, Leptodactylas
mystacinus, stirs up a frothy mass of mucus,fills it in holes near water and lays eggs in
them. The tadpoles developing in these nests can readily enter water.
Mud nest: Hyla fabre, the male digs a little crater like hole or nursery in mud in shallow
water, in which the female lays eggs. Tadpoles hatch within this relatively safer barrier
and develop until they are large enough to defend themselves.The South American tree
frog, Phyllomedusa hypochondrales. Lays eggs in a folded leaf nest with margins glued
together by clocal secretion. The tadpoles when formed fall straight into water below.
Gelatinous bags. Salamandrella keyserlingi will construct a gelatinous bag like
structure. It is attached to an aquatic plant below the water. In this bag eggs are stored.
Thus they are protected by the enemies.
(ii) Direct carrying by parents
Coiling around eggs :The female Icthyophis glulinosa will dig a hole in the moist soil
near a pond. It will deposit eggs in it. Around this egg mass the mother will coil and
protect the egg mass until they hatch and protect from the enemies. The female of
Salamander , Plethodon also coils round the eggs which are laid in small packages in the
hollow of a rotton log or beneath a rock (Fig. A).
Transferring tadpoles to water: Some species of small frogs (eg Phyllobates,
Arthroleptis, Pelobates, Dendrobates) in both tropical Africa and South America, deposit
their eggs on ground. The tadpoles hatching out , fasten themselves to the back of one of
the parents with their sucker-like mouth and transported to water (Fig3 B).
Eggs glued to body: Many amphibians, instead of remaining with the eggs,carry the
eggs glued to their body. In the dusky salamander, Desmognathus fuscus, female carries
the string of eggs coiled around her neck, until they have hatched. Rhacophorus
reticulates, the eggs are glued to the belly of female. In European mid wife toad, Alytes
obstetricans, when the female lays eggs, the male entangles them around his hindlegs.
He carries them with him until they are ready to hatch. He releases the tadpoles into
nearest water (Fig3D).
Eggs in back pouches: In tree frog (marsupial frog), the female carries the eggs on her
back, either in an open open oval depression,a closed pouch or in individual pockets. The
eggs develop into miniature frogs before they leave their mother’s back. In Nototrema,
the eggs are covered by skin forming a single large brood pouch which opens posteriorly
in front of the cloacal aperture (fig3F). In aquatic Surinam toad, Pipa, in breeding
season, Skin of female’s back become thick, vascular, soft and gelatinous. The male
presses fertilized eggs against female’s back, where they sink into individual pits. A
hinged cover forms over each egg enclosing it in a small capsule. Complete
metamorphosis occurs with capsules. The tiny toads leaving mother are tailless and do
not enter water (fig3 G).
Organs as brooding pouches: South American Darwin’s frog, Rhinoderma darwinii,
pushes fertilized eggs into his large vocal sacs and here they undergo complete
metamorphosis to emerge out as fully formed froglets.
Viviparity: Some anurans are ovoviviparous. They retain eggs in the oviducts and the
females give birth to living young. African toads, Nectophrynoids and Pseudophryne give
birth to living young.
Protection by nest
Direct parental care in amphibian:
Ans (5)
Poisonous snakes
Common poisonous snakes are cobras, krais, pitIess vipers, pit vipers, sea snakes and
coral snakes. All have poison glands and some of their maxillary teeth modified into
fangs. Their tails are cylindrical, except in sea snakes. Heads are covered with shields
(not scales) and ventral shields cover the entire width of belly. Their other special
characteristics are as follows:
Cobras. The common Indian cobra is Naja naja or Naja tripudians. It is the most
cornmon and deadly poisonous snake of India, Length is about 2 metres and black or
brown colour. Head is small and indistinct and pupil is round. Neck can dilatate into a
hood supported by ribs and may bear spectacle marks dorsally. The 3rd supralabial shield
of upper lip touches eye and nasal shield. Subcaudal shields are in 2 rows. Fangs are
anterior, grcoved and permanently erect.
Largest and deadliest snakes is the King cobra or hamdadryad Ophiophagus hannah, also
known as Naja Hannah or Naja bungarus. It lives in deeply forested areas and grows to
about 4 metres.
Kraits. Kraits occur all over India. The common krait, Bungarus caeruleas, grows to a
length of 1.2 metres. Vertebrals are large and hexagonal. 4th infralabial is the largest.
Subcaudals are single. Their fangs are small and wounds inflicted superficial, but poison
is three times as virulent as that of cobra. lts body is marked with alternate broad black
and yellowish rings imparting a beautiful but dreadful appearance.
Pitless vipers: The largest Indian pitless viper is the Russel's viper. It is about 1.5 metres
long. Its head is distinct, triangular, flat and covered with small scales. Nostrils are
lateral, oblique and very large. Upper, surface of body shows three rows of large black
rings appearing like chains, hence the common name chain viper. Head shows a yellow A
-mark' and subcaudal shields are in 2 rows. Fangs are large, tubular (solenoglyph) and lie
down when not in use. It marks a loud hissing sound when attacked. It is noctumal,
viviparous' thoroughly terrestrial and feeds chiefly on mice
Pit vipers. Pit vipers differ from pitless vipers in having a loreal pil between the eye and
nostril on either side. The loreal pits form heat sensitive organs But they resemble pitless
vipers in the possession of a robust body, triangular head with scales, broad, Solenoglyph
fangs.
Ancistrodon (Agkistrodon) himalayanus the brown Himalayan' pit viper of India' is very
common in eastern hills as well as in Kashmir and grows to nearly 70 cm.Its head bears
shields, subcaudals are in 2 rows and tail ends in a long spine-like scale. In A. hyprule of
South India, snout is bossy and slightly turned upwards.
Lachesis (Trimeresurus) strigatus, also common in South India, grows to about 45 cm. Its
Snout has .shields, rest of the head bears scales. Slightly prehensile tail ends in a conical
scale. Colour is brown with irregular dark spots. Neck bears a white horse-shoe mark. A
dark brown band runs behind each eye.
The famous rattle snake (Crotalus) of North America is easily distinguished by the
presence of a rattle at the end of tail. It consists of 10-12 horny hollow segments loosely
held together During locomotion, the rattle strikes ground producing a rattling sound.
Before, striking the rattle vibrates producing a buzzing sound which serves.as a warning.
Water snakes: Water snakes mostly found near water sources. It may be identified by
rather short and stout body and a long tail. The fresh water snakes are all nonpoisonous,
However some sea snakes are poisonous'. Water snakes' particularly the sea snakes have
bright colours ranging from many shades of yellow to olive brown. The common fresh
water snake is Xanochrcphis piscater also known as 'checkered keel back' as it has the
dorsal spots arranged in series forming a class board pattern, which can be identified by
characteristics sound, pupils with speckled greenish goIden area around thcm. Nosrils are
placed high in the snout, which facilitate respiration in water. Sea snakes inhabit tropical
parts of Indian and Pacific Oceans. They pass their whole life in sea water and poisonous.
They look eel-like and are easily identified by their elevated and laterally compressed
oar-like tails, suited for swimming. Eyes are small with rounded pupil. Nostrils are
valvular and lie at the tip of snout to permit breathing while in water.
Fig: Poisonous snakes of India
Ans (6)
General characters of the reptiles
Body varied in shape, covered with horny epidermal scales, sometimes with dermal
plates; integument with few glands.
Paired limbs, usually with five toes with claws, adapted for climbing, running or
paddling; limbs absent in snakes and some lizards.
Skeleton well ossified; ribs with sternum except in snakes, forming a complete thoracic
basket; skull with single occipital condyle.
Respiration by lungs:
· Three-chambered heart, except in crocodiles which have four-chambered heart.
· Metanephric kidney; uric acid is the main nitrogenous waste.
· Ectothermic animals.
· Nervous system with primitive brain, spinal cord dominant. There are 12 pairs of cranial
nerves.
· Sexes separate; fertilization internal, hemipenis as copulatory organ.
· Eggs covered with calcareous or leathery shells. Extra embryonic membranes, amnion,
chorion, yolk sac and allantois are present during embryonic
The upper part of the skull of reptiles is modified giving the reptiles a far more
efficient and powerful jaw action and making the skull light. The reptiles are classified
mainly on the structure of their skulls, in which there are temporal vacuities or fossae or
empty spaces in the temporal region. The function of these temporal fossae was probably
to enable the jaw muscles to protrude out onto the upper surface of the skull. In this way,
the jaw muscles could be made much longer, giving a far more powerful jaw action.
Three different groups of reptiles developed fossae in different places, parapsid, synapsid
and diapsid types, and these remained unchanged throughout the evolutionary history of
these groups.
Subclass 1. Anapsida ; Primitive reptiles with a solid skull roof . No temporal opening
Order 1. Chelonia: Body short. Broad and oval
2. Limbs clawed and/or webbed, paddle like
3. body enclosed in a firm shell of dorsal carapace and ventral plastron, made of dermal
bony plates. Thoracic vertebrate and ribs usually fused to carapace.
4. Skull anapsid with a single nasal opening and without a perietal,foramen.
5. Jaws with horney sheath.
Subclass II Euryapsida (extinct): skull with a single dorso lateral temporal opening on
either side, bounded below by postorbital and squamosal bones
Subclass III. Parapsida(extinct) These are reptiles with one temporal fossa, placed high
up on the skull. Two largest groups – the ichthyosaurs and the plesiosaurs. These two
lines of reptiles became modified for aquatic life in quite different ways but they share
the same basic type of skull organisation, with minor differences. Both Ichthyosaurus and
the Plesiosaurus became extinct at the end of the Cretaceous when many other terrestrial
reptiles including dinosaurs died out.
Subclass IV: Synapsida (extinct): Skull with a single lateral opening on either side
bounded above by the postorbital and squamosal bone
Subclass V. Diapsida : Skull with two temporal openings on either side separated by the
bar of postorbital and squamosal Bones.
Order: 2 Rhynchocephalia (rhynchos, snout)
1. Body small, elongated lizard like
2. Limbs pentadactyle, clawed and burrowing
3. Skull Diapsid, Nasal openings separate,
4. Teeth acrodont
5. No copulatory organ in male
This order contains only two species that live on some islands off the coast of New
Zealand. They look like lizards but there are differences that set the tuatara or Sphenodon
punctatum apart from lizards. The tuatara spends daytimes in burrows. It comes out in the
evening to feed on insects and other invertebrates.
Order: 3 Squamata
The order includes Lizards and snakes, which are creepers and inhabit a variety of
habitats. Snakes are carnivorous but lizards eat a variety of foods including plants and
insects. Snakes have descended from lizards and there are many similarities between
them.
1. Exoskeleton of horney epidermal scales, Shields and spines Skull Diapsid
Snakes do not have eyelids but lizards have.
Snakes usually have one row of scales on the belly; lizards have many.

Snakes do not have legs, most lizards have legs.
 Snakes have jaw bones that disarticulate allowing them to swallow large objects.
Lizard jaw bones do not disarticulate.
Order Crocodilia
This order includes alligators, caimans, crocodiles and gharials that are found in and near
water in warmer areas of the world. They eat fish, birds, turtles, and mammals.
Members of the crocodile group have legs and feet designed for walking on land and a
strong flattened tail used for swimming. The three groups are distinguished from one
another by the shape of their heads. Alligators have a broad, rounded snout; while the
crocodiles have a triangular head with a more pointed snout and gharials have a very long
and narrow snout.
A=Anapsid
B= Synapsid
c=Diapsid
Ans (7)
Mammals show many variations in the mode of origin and details of shape and structure
of placenta, which are classified accordingly. The three main factors involved are : (i)
Nature of extra-embryonic membnanes involved are (i) Nature of extraembryonic
membranes involved (ii) distribution of villi and shape of placenta and (iii) degree of
intimacy between foetal and maternal tissues
Types according to extra-embryonic membranes involved or mode of origin
Depending on the foetal membranes forming placenta, three kinds are recognized : yolk
sac, Allantoic and chorionic .
Yolk sac placenta : In Metatheria or marsupials, such as kangaroo (Macropus) and
opossum (Didetphvs), placenta is derived from yol sac and chorion. Yolk sac developed
from the lower part blastocyst is very large and nearly encloses the entire embryo and its
amnton. Wall of yolk sac lies in direct contact with chorion (trophoblast) which sends out
finger-like villi into uterine wall Yolk sac wall also develops vitelline blood vessels for
transporting secretions. Uterine milk absorbed from uterus to the developing embryo.
Allantois remains poorly developed and never comes in contact with chorion
In Metatheria, yolk sac placenta is weakly developed so that embryonic nutrition and
growth remain limited and the young is born very small and immature. To compensate
the deficiency of intra –uterine development, it is transferred to the abdominal pouch or
marsupium and fed on milk until fully formed.
In some eutheria, a yolk sac placenta is usually not found. But, it may be large and
temporarily develop in early stages in some mammals such as hedgehogs and rabbits. Or
it may be small ending in a small tube in the umbilical cord, as in man.
Allantoic placenta. In the majority of Eutheria, the chief organ of embryonic nutrition is
the allantoic placenta consisting of allantois and chorion. Allantois is a sac-like
outgrowth from the hindgut of embryo. It is lined internally by endoderm and externally
by mesoderm. As allantois grows and spreads in the extra-embryonic cavity, its
mesoderm fuses with that of chorion over a somewhat restricted region. The layer formed
by fusion of allantois and chorion is termed allanto-chorian. It becomes richly vascular
and thrown into small, finger-like processes, the villi. The uterine wall forms
corresponding depressionsc, alled crypts, which are penetrated by foetal villi forming
allantoic placenta. Materials absorbed frorn maternal blood through allantoic placenta are
carried to the foetus by allantoic blood vessels. Outside Eutheria, a primitive allantoic
placenta occurs only in Perameles (bandicoot) which is a metatherian. But it also has an
efficient yolk sac placenta. In this case yolk sac and allantois are large, well developed
but it is allantois that supplies blood vessels to chorion. The trophoblast of the chorion, at
placqs of contact with uterine wall disappears. The uterine wall is syncytial and highly
vascularised. Physiological exchange takes place between the foetal blood and maternal
blood.
Chorionic placenta. It occurs in man and apes and is formed only by chorion. Allantois
remains small, bunows into body stalk (umbilical cord) and does not reach chorion.
However, its mesoderm and blood vessels grow up to chorion whose villi enter the
uterine crypts forming chorictnic placenta.
Fig: Yolk sac placenta of opossum
Fig: Allantoic placenta of pig
Fig: Chorionic placenta of man
Types according to shape and distribution of villi
Depending on the shape of placenta, manner or distribution of villi, degree of connection
berween foetal and maternal tissues and behaviour of placenta at the time of birth, the
following types and subtypes of allantoic placenta can be recognized ( Fig. 5) ,
(i) Non-deciduous placenta. In most mammals villi are simple, unbranched and merely
apposed without intimate contact between foetus and uterine wall. At the time of birth or
parturition, villi are .easily withdrawn from maternal crypts without causing any tissue
damage. Thus no part of uterine tissue comes out and no bleeding occurs. Non-deciduous
or non-deciduate placenta has following subtypes according to the manner of distribution
of villi.
(a) Diffuse. Villi remain scattered all over the surface of allantochorion. Ex. Pig, horse,
lemur.
(b) Cotykdonary. Villi ,are arranged in separate tufts or patches called cotyledons. Ex.
Goat, sheep, cow, deer.
(c) Intermediate. Villi are arranged in cotyledonsa s well as scattered. Ex. Camel,giraffe.
(ii) Deciduous placenta. Villi are complicated,branched and intimately connected. At
birth, a variable amount of maternal tissue is pulled out with the shedding of blood.
Deciduous or deciduate placenta is also differentiated in the following subtypes:
(a) Zonary. Vlli form an incomplete (e.g. racoon) or complete girdle encircling the
hlastocyst.E x. cat, dog, seal,e lephant.
(b) Discoldal Villi are restricted to a circular disc or plate on the dorsal surface of
blastocyst.Ex. insectivores, bats, rodents (rat, mouse), rabbit bear.
(c) Metadiscoidal. Villi are at first scatrcred but later become restricted to one or two
discs. It is monodiscoidal in man and bidiscoidal in monkeys and apes.
Contra-deciduous. Foetal villi and uterine crypts are so intimately connected that even
most of foetal placenta is left behind at birth to be broken and absorbed by maternal
leucocytes. Ex. Bandicoot (Perameles), mole (Talpa).
Fig: 5 Types of placenta according to villi.
Ans 8