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INVERTEBRATA
Biology Class IX
7/15/2015
Educast
Lubna Naz
Chapter #7
INVERTEBRATA
Contents:
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
Invertebrates
Phylum Protozoa
Phylum Porifera
Phylum Coelenterata
Phylum Platyhelminthes
Phylum Nematoda
Phylum Annelida
Phylum Arthropoda
Phylum Mullusca
Phylum Echinodermata
Invertebrates
The animal kingdom is informally divided into two groups, the vertebrates and invertebrates.
Invertebrates are a group of animals that have no backbone, unlike animals such as reptiles,
amphibians, fish, birds and mammals who all have a backbone.Invertebrates are a group of
animals that have no backbone, unlike animals such as reptiles, amphibians, fish, birds and
mammals who all have a backbone.
1. PHYLUM PROTOZOA
If you take a drop of pond water and observe it under the microscope, you can often see tiny little
organisms
swimming
around.Protozoa,
as
traditionally
defined,
are
mainly microscopic organisms, ranging in size from 10 to 52 micrometers.
LOCOMOTION IN PROTOZONS
The group includes flagellates (which move with the help of whip-like structures
called flagella), ciliates (which
move
by
using
hair-like
structures
called cilia)
and amoebae (which move by the use of foot-like structures called pseudopodia). Some protozoa
are sessile, and do not move at all.
Pellicle
The pellicle is a thin layer supporting the cell membrane in various protozoa, such as ciliates,
protecting them and allowing them to retain their shape, especially during locomotion, allowing
the organism to be more hydrodynamic.
examples of protists with a pellicle are the euglenoids and the ciliate Paramecium.
Euglena
Euglena isan enigmatic organism with a curious mixture of plant and animal characteristics, and,
therefore, sometimes is considered to represent a borderline case between the plant and animal
kingdoms. The active swimming movements result from the beating of the long flagellum, which
pushes the organism through the water. A second, shorter flagellum is present within the flagellar
pocket, but does not aid in the swimming movements. this movement is called euglenoid
movement.
Phylum Cnidaria (Coelenterata)
MAIN CHARACTERS
HABIT AND HABITAT
They are aquatic animals, mostly marine and few fresh water forms. They are sedentary or free swimming and solitary or colonial
STRUCTURE
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The cnidaria are metazoa having the simplest type of body wall consisting of two layers.
The outer epidermis and the inner gastrodermis which lines the body cavity.
In between the two layers lies the mesogloa, non-cellular jelly secreted by them.
Cnidarians, due to their two layers body wall are termed as diploblastic animals. All other
metazons possesses a third layer called mesoderm in their body wall, laying in between
the epidermis and gastrodermis (Endoderm) and are therefore called Triploblastic
animals.
They have radially symmetrical body plan organized as a hollow sac.
The mouth is surrounded by a circle of tentacles bearing cnidoblasts stinging cells
containing nematocysts.
They have central digestive cavity connected to the outside by mouth.
STRUCTURAL TYPES
The Cnidarians are radially symmetrical and occur in two types of forms.
(a) The polyp
(b) The Medusa
(A) POLYP
The polyp like Cnidarian for example sea anemone has a cylindrical body with a mouth directed
upwards and surrounded by tentacles. The basal surface of the body is attached to the
substratum.
(B) MEDUSA
The medusa like Cnidarians jelly fish are umbrella like in appearance. Their oral surface, bearing
the mouth is directed downwards.
PROCESS OF FEEDING AND DEFENCE
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The Cnidarians feed mostly on animal diet.
The food is digested in the gut and the waste products are expelled through the mouth.
The Cnidarians so named, because they possess cnidoblasts bearing nematocysts which
help in feeding and defence.
PHYLUM PLATYHELMINTHES
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The name Platyhelminthes means flat worms; there are about 15,000 living species.
They live in marine and fresh water habitats, moist terrestrial environments, and inside other
organisms as parasites. All have three tissue layers: ectoderm on the outside, endoderm lining
the gut, and mesoderm in between. As in the Cnidaria, the gut is a gastrovascular cavityand
has the functions of both digestion and circulation; the mouth serves as both entrance and exit
from the gut. The body is bilaterally symmetrical, and there is a well defined rostral or head
end and, opposite it a caudal or tail end. At the head end the nervous system has a coordination
center which can be called a brain. There is no specialized respiratory system.
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Flatworms are acoelomate, that is the outside of the gut wall is directly continuous with
the mesoderm; there is no coelomic cavity and so the gut is not free inside the body. The
mesoderm is muscular and is used for movement. Ectodermal cells may be ciliated and provide
another means of locomotion.
The Phylum Nematoda
Etymology:- From the Greek Nema for Thread and Eidos for form.
Characteristics of Nematoda:1)Bilaterally symmetrical, and vermiform.
2)Body has more than two cell layers, tissues and organs.
3)Body cavity is a pseudocoel, body fluid under high pressure.
4)Body possesses a through gut with a subterminal anus.
5)Body covered in a complex cuticle.
6)Has a nervous system with pharyngeal nerve ring.
7)Has no circulatory system (no blood system)
8)Reproduction normally sexual and gonochoristic.
9)Feed on just about everything.
10)Live just about everywhere, many species are endoparasites.
The Phylum Annelida
Characteristics of Annelida:1)Bilaterally symmetrical and vermiform.
2)Body has more than two cell layers, tissues and organs.
3)Body cavity is a true coelom, often divided by internal septa.
4)Body possesses a through gut with mouth and anus.
5)Body possesses 3 separate sections, a prosomium, a trunk and a pygidium.
6)Has a nervous system with an anterior nerve ring, ganglia and a ventral nerve
chord.
7)Has a true closed circulatory system.
8)Has no true respiratory organs.
9)Reproduction normally sexual and gonochoristic or hermaphoditic.
10)Feed a wide range of material.
11)Live in most environments.
The Phylum Arthropoda
Characteristics of the Arthropoda:1)Bilaterally symmetrical (in most cases).
2)Body has more than two cell layers, tissues and organs.
3)Body cavity a true coelom.
4)Most possesses a through straight gut with an anus (in most cases).
5)Body possesses 3 to 400+ pairs of jointed legs.
6)Body possesses an external skeleton (in most cases).
7)Body is divided in 2 or 3 sections.
8)Nervous system includes a brain and ganglia.
9)Possesses a respiratory system in the form of tracheae and spiracles (in most cases).
10)Possesses a open or lacunnar circulatory system with a simple heart, one or more
arteries, and no veins, (in most cases).
11)Reproduction normally sexual and gonochoristic, but can be parthenogenetic.
12)Feed on everything.
13)Live everywhere.
Complete Metamorphosis
Complete metamorphosis is characteristic of beetles, butterflies and moths, flies, and wasps.
Their life cycle includes four stages: egg, larva, pupa, and adult. The larva differs greatly from
the adult. It is wingless, and its form and habits are suited for growth and development rather
than reproduction. The change to the adult occurs during the inactive, nonfeeding pupal stage. At
this time the larva undergoes a transformation in which the wings appear externally, larval
organs and tissues are broken down, and adult structures are developed. Hypermetamorphosis, a
form of complete metamorphosis, occurs in some beetles, flies, and other insects and is
characterized by a series of larval stages.
Incomplete Metamorphosis
Incomplete metamorphosis only has three life cycle stages:
 egg
 nymph
 adult
The nymph looks like a smaller version of the adult, but is wingless. Instead of going into a
cocoon, the nymph grows into an adult by shedding its outer layer or exoskeleton. Once wings
develop, the nymph has become an adult and will no longer shed its outer shell.
Echinodermata
Echinoderms are invertebrate marine animals that are found in all oceans of the world and at all
depths.
There
are
no
echinoderms
in
freshwater
environments.
Members of the Phylum Echinodermata include many easily recognizable creatures such as sea
stars (or starfish), brittle stars, sea urchins, sea cucumbers, and sea lilies. All of these animals are
radially or biradially symmetric and they fill a variety of niches in marine environments as
particle feeders, browsers, scavengers, and predators.