Classes of vertebrates

Vertebrates are divided into five classes viz:

·
Class Pisces
e.g. Fish

·
Class Amphibian e.g. Toad

·
Class Reptilia
e.g. Lizard

·
Class Aves
e.g. Bird

·
Class Mammalia e.g.
Goat, guinea pig

Pisces (True Fishes)

Characteristic

A fish has the following characteristic it is a cold
blooded (poikilothermic) animal, i.e. its body temperature varies with that of
its surrounding.

·
Respiration is through the gill a well developed
sense of smell and a lateral line system.

·
Fertilization is external.

·
All are aquatic i.e. they live in water

·
Possesses streamlined bodies shark.

·
Possesses a swim bladder which regulates its
density so that it can rise and sink in the water e.g. Tilapia, cod fish.

·
Most of them have scales, e.g. tilapia others
are scaleless, (cat fish)

Two major sub-groups of Pisces (fishes) exist

(a) Chondrichthyes – These are fishes with
skeleton of cartilage e.g dog fish, sharks, dolphins etc.

(b) Osteichthyes –
These are fish with a skeleton of bone and swim bladder e.g. Tilapia cod
fish etc.

Amphibians

·
They are cold – blooded animals (poikilothermic)

·
Has a paired fore and hind limbs and (webbed toe)
in the adult stage.

·
Has a naked, moist skin

·
Has sticky tongue which can be protruded and
retracted quickly.

·
Has inner and middle ears.

·
Respiration is through gills, lungs, skin or
mouth liming, separately or in combination. Gills are present at some stage in
its life cycle e.g. toad, salamander

·
Has a 2 chambered heart in the larva stage and 3
chambered heart in the adult stage.

·
Fertilization external they feed on insects
small worms snails etc.

Reptilia (Reptiles)

·
Has a skin that is covered with dry horny
scales.

·
Respiration is through the lungs

·
Fertilization is internal most members are
oviparous.

·
The male has a copulatory organ (penis)

·
They are cold-blooded animals

·
Has an incompletely developed four chambered
heart

·
Has a jaw with the same teeth embedded in socket

·
Has a well developed tongue which can be
protruded and retracted quickly.

·
Has paired fore and hind limbs each with five
toes ending in claws (except snakes that moves by means of scutes (scale on the
belly)

·
Has middle and inner ear.

Example includes features
of the agama lizard.

Aves (Birds)

This class includes all types of
birds, both flightless and flying birds.

Characteristic

·
They are warm – blooded (homoeothermic)
vertebrate.

·
Has head, neck and trunk that are covered with
feathers, its hind legs with scale red wings for flying

·
Has hind legs with feet, each with four toes
ending in claws

·
Has a mouth with a toothless break for feeding

·
Has four chambered heart e.g. ostrich, duck

·
Breaths with the lungs

·
Fertilization is internal

·
Has a rigid skeleton

·
They are mostly terrestrial (live on land).

·
They are oviparous

Examples includes; pigeon,
duck, ostrich, kiwi

Classification of Birds

·
Perching birds e.g. sparrow, king fishers

·
Birds of prey e.g. Eagles, hawks, vulture

·
Water birds e.g. ducks, swans, flamingos

·
Non-flying birds e.g. ostrich.

Mammalia (Mammals)

This class are made up of the more advanced animals.

Characteristics

·
They are warm blooded (Homoiothermic) animals.

·
Has sweat and sebaceous glands.

·
Has hairs for growing from the skin

·
Has external ears called pinnal.

·
Has a well developed heart

·
Has a well developed brain

·
They are viviparous (their young one’s are born
alive) except the monotremes which lay eggs

·
Has a body cavity separated by diaphragm into
two (thoracic cavity and abdominal cavity).

·
Fertilization is internal

·
They possess two pairs of limbs.

Classification of Mammals

Mammals are
classified according to their mode of living feeding and breeding habits. viz;

(a)
Monotremes – These are primitive and egg laying
mammals e.g. duck– billed platypus, spiny ant ester.

(b)
Marsuplasis – These are pouch mammals with
rudimentary non – allantonic placenta e.g. opossums, kangaroos etc

(c)
Eutherrians – These are mammals with true
placenta. their young ones develop in the uterus with the female body. They
obtain food and oxygen through the placenta and they are born alive among the
groups are;

·
The
toothless mammals e.g. the armadillo

·
Mammals that eats insects e.g. Moles, Hedge hags
etc.

·
Sea-living mammals – e.g. Dolphins whales

·
Carnivorous mammals – wolves, foxes, dogs bears,
lion, tigers etc

·
Gnawing mammals (Rodents) e.g. Mice, rat,
squirrels etc

·
Herbivorous animals (mammals with hoots) e.g.
horses, pigs, sheep, cows etc

·
Mammals that fly e.g. Bats.

·
Mammals with trunks e.g. elephants

·
Primates – mammals with flexible fingers and
well developed brain e.g. man, monkeys, chimpanzees, baboons, gorillas etc

There are invertebrate aquatic animals found mainly in the
sea e.g. jelly fish etc. They posses the following characteristic:

·
They are multi cellular organism

·
They have a hollow- like sacs with single
opening i.e. the mouth.

·
They posses stinging cells nematocysis which
serve as protection

·
Have one body cavity called enteron

·
They live in fresh and salt water

·
They posses tentacles in their mouth region used
to direct food into the mouth.

·
They have two distinct body layers called
ectoderm and mesogloea.

Example includes: jelly fish,

· They possess specialized
cell e.g. sensory cells granular cells, nerve cells and absorptive stinging
cells.

· Has no blood, respiratory
or excretory organ.

· They have thin flat bodies.

Phylum Mollusa (soft
bodied, typically with shell)

They are invertebrate terrestrial animals.

They possess the following
characteristic:

·
They have a soft – slimy foot used for burrowing
swimming and crawling.

·
They possess soft and unsegmented body

·
Respiration is through a lung in the mantle
cavity

·
Most members possess a pair of tentacle with
eyes which is with drawn when touched.

·
Some have calcareous shells secreted by the
mantle which protect them from drying out, predators and damage.

·
Have a coiled shell (e.g. snail) others have two
shells e.g. oysters, while some don’t have shells e.g. octopus and slugs.

·
Reproduce sexually. The sex organ for male and
female are separate.

·
Body is covered by a soft tissue called mantle.
The mantle cavity is found between the body contains the internal organs

·
Examples of molluscs includes snails, oyster ,
octopus, scallops, mussels etc.

Phylum Annelida (Segmented worms)

These are invertebrates animals commonly called true worms.
They poses the following characteristic:

·
Have well developed nervous circulatory system

·
May be male, female or hermaphroditic

·
Reproduce sexually

·
Respiration is through the moist skin covering
the body.

·
Some organs (gut nerve cord and blood vessel)
runs the whole length of the body

·
They live in the soil (e.g. earth worm) under the
sand/mud in the sea (e.g sandworm) and others.

·
Have a true body cavity called coelom with a
distinct head.

·
Examples includes, earthworm, sandworm leeches.

·
Body is cylindrically segmented by septa
(partitions). The segment have identical organs.

·
They have alimentary canal with mouth and anus

Phylum Anthropoda

These are invertebrate animals: it is the largest phylum
in the animal kingdom and is divided into the following classes; crustaces, insecta, Aractinida and myriapoda. They
possess the following characteristic:

· Have segmented bodies,
which are grouped into three to form a head a thorax and an abdomen. In most
cases, the head and thorax are fused together to form a cephalothorax (e.g.
tick, spider, crab)

· Their body are enclosed in
a hard and rigid exoskeletons made of chitin which protects them from
predators.

· Each segment usually bears
a pair of jointed appendages, which may be used for feeding, moving or as
sensory organs.

· They possess well,
developed sensory organs e.g. a simple and compound eyes and antenna

· Sexes are separate often,
the male and female look different

· Have specialized digestive
and respiratory system.

· They are divided into four
classes

Phylum Platyhelminthes (flat worm)

Platyhelminthe or flat worms
are invertebrate animals among the most primitive groups of animals to have
bilateral symmetry. They possess the following characteristic

· Body is bilaterally
symmetrical

· Have no digestive system
and lack anus

· They have slender, broadly,
leaf like or ribbon like body

· They range in size from
less than a millimeter to several meters (e.g. tape worms measures 75 meters)

· They possess excessive
reproductive capacity.

· Reproduction is sexual,
some hermaptrodites

· They have definite head and
tail end.

· Most are free – living (e.g
planaria), others are true parasite e.g. tape worms, fluke etc

· They possess adhesive
organs such as sucker

· True parasitic
platyhelminthes are classified into

(a)
Cestodes e.g tape worm

(b)
Termatodes e.g fluke

(d)
Turebella

The cestodes (tape worm)

Cestodes or tapeworm are invertebrate endo-parasites,
which as adult lives in the intestine of vertebrate host. Several species are
capable of parasitizing humans.

Characteristic of cestodes

Tape worms have segmented, elongated, and flattened
leaf like or ribbon – like head called scolex which bears two or more rows of
hooks attached to the rostellium and suckers for clinging to the intestinal
well host. (not all species have hook and sucker, like the fish tapeworm has
only scolex.

There is no mouth or
digestive system. The nutrient are beef tape worm has only sucker and pork tape
worm has both hook and sucker.

Absorbed directly through
body surface of the worm. The head is attached to a neck which generates the
new body segments or proglottids (also called stobila). Each matured
proglottids bars a complete male and female organs, hence tape worms are
hermaphrodites. The posterior lend of a matured proglottid contains eggs and is
described as a gravid proglottids. The adult are seen in the intestine where as
larva develop in the tissue of the host, either vertebrate or invertebrate
animals