PHYLUM-ECHINODERMATA
Phvlum—Echinodermata (Echinos —spines; derma—skin)
includes the spiny skinned animals, which are exclusively
marine. Jacob Klein ( 1734) coined the term ‘Echinodermata’.
It includes about species.
General Features
Some important general features of phylum—Echinodermata are
discussed below
(i) Habit and Habitat These are marine forms and are
bottom dwellers.
(ii) Symmetry The adults have radial (pentamerous)
symmetry but, the larval forms have bilateral symmetry.
(iii) Germ Layers and Organisation They are triploblastic
and exhibit organ system grade of organisation.
iv) Head It is absent in echinoderm and body also lacks
segmentation.
(v) Body Cavity They have true coelom, which is
lined by a ciliated peritoneum. The most
distinctive feature is the presence of water
vascular system or ambulacral system with tube
feet that help in locomotion, capture of food and
respiration.
(vi) Endoskeleton It contains numerous calcareous
plates called ossicles beneath the skin.
(vii) Locomotion The locomotion is carried out by
tube feet.
(viii) Digestion The digestive tract is simple and
complete type. The mouth is present on the
lower side and the anus is on the upper side.
(ix) Respiration It occurs through tube feet, which
help in respiration.
(x) Circulation It is reduced and open type called as
haemal system.
(xi) Excretion The excretory organs are absent. The
waste products are removed by diffusion through
branchiae or amoebocytes.
(xii) Nervous System It contains circum-oral nerve
ring, transverse and radial nerves.
xiii. Reproduction Echinoderms reproduce sexually
Sexes are separate and show no sexual
dimorphism. Fertilisation is external and
development is indirect, e.g., Asterias, (seastar or
starfish), Ophiura (brittle star), Echinu
(sea urchin),
Cucumaria (sea cucumber), Antedon (feather star
or sea lily).

PHYLUM-ARTHROPODA
Phylum—Arthropoda (Arthron jointed; podos foot)
includes the first and simplest segmented animals. These are
commonly called as jointed legged animals. It is the largest
group of animal that includes about 1000000 insect species,
102248 spiders and scorpion species, 103248 arachnoid
species and 47000 crustacean species representing about
80% of total known animal species.
General Features
Some important general features of phylum—Arthropoda
are discussed below
(i) Habitat and Habit They may be aquatic or
terrestrial. They may occur as free-living or parasitic
forms e.g., bed bugs, ticks, mosquitoes, etc.
(ii) Body Parts Body is segmented externally. It has distinct
thorax and abdomen. Head bears many fused
segments and sense organs.
(iii) Symmetry and Body Organisation Arthropods are
bilaterally symmetrical, They are triploblastic with
organ system level of organisation.
(iv) Appendages They have jointed, paired appendages,
which are present in some or all somites or segments.
These perform various functions like walking
clinging, jumping, feeding, etc.
v) Exoskeleton The exoskeleton is formed of thick,
tough and non-living chitinous cuticle.
Exoskeleton protects animal from mechanical and
chemical injuries, prevents desiccation and also helps
in attachment.
i) Locomotion Jointed appendages help in
locomotion. Cilia are found to be absent in
arthropod.
(vii) Digestive System Alimentary canal is complete and
well-developed, i.e., divided into foregut, midgut
and hindgut.
(viii) Respiration It occurs through general body surface’
gills (e.g., prawn), book lungs (e.g., scorpion an
spider), trachea (e.g., cockroach) and book gills (e•g.,
king crab).
(ix) Circulation The circulatory system is open type,
i.e., blood flows in the haemocoel instead of blood
vessels.
(x) Excretion The excretory organs are Malpighian
tubules (opening into duct) or green glands opening
directly to the exterior.
(xi) Nervous System The nervous system consists of a
nerve ring and a double ganglionated ventral nerve cord.
(xii) Sense Organs Arthropods have simple eyes called
ocelli and compound eyes.
Aquatic forms have statocysts for balancing.
(xiii) Reproduction Arthropods reproduce by sexual
methods. Fertilisation is usually internal type. They
are generally oviparous but few are viviparous, i.e.,
scorpion. Development may be direct or indirect
involving metamorphosis.
(xiv) Classification The phylum—Arthropoda is divided
into five classes
Class—Crustacea, e.g., Palaemon (prawn), crab, etc.
Class—Myriapoda, e.g., Scolopendra (centipede),
Julus (millipede), etc.
Insecta, Musca (homefly), Apis (honeybee),
Pest-Locusta (locust), Vector-Mosquitoes
(Anopheles, Culex, Aedes), etc. e.g., spider, ticks,
mites, Limulus (king crab),
Economically important insects are
Apis – Honeybee
Bombyx – Silkworm
Laccifer – Lac insect
Limulus(king crab) is living fossil from Arthropoda
phylum.

PHYLUM-ASCHELMINTHES
Phylum—Aschelminthes or Nemathelminthes or Nematoda
(Nema — thread; helminth — worms) includes roundworms
They are commonly called as nematodes.
General Features
Some important general features of phylum—
Aschelminthes are discussed below
(i) Habitat and Habit They are mostly free-living and
may occur in water or within the soil. There are
several parasitic species which live within the body Of
animals or plants, e.g., Guineaworms, whipworms
eyeworms, etc.
(ii) Symmetry They show bilateral symmetry and have
organ system level of organisation.
(iii) Germ Layers They are triploblastic animals and have
tube within tube body plan.
(iv) Body Wall The body wall contains an outer cuticle,
syncytial epidermis and a muscle layer. Circular
muscles are absent.
(v) Body Cavity Aschelminthes are pseudocoelomates as
the cavity present between the body wall and gut is not
lined by mesodermal epithelium.
(vi) Digestive System Alimentary canal is complete with a
well-developed muscular pharynx.
(vii) Excretory System It consists of a pair of gland cells or
intracellular canals or both.
(vii) Nervous System It contains a nerve ring around the
pharynx with dorsal and ventral longitudinal nerve
cords running throughout the length of the body.
ix) Reproduction Nematodes reproduce only by sexual
method. Sexes are separate and exhibit sexual
dimorphism. The males are generally smaller than the
females to aid copulation.
(x) Fertilisation It is internal. The fertilised eggs develop
directly or indirectly through larvae that undergo
moulting and finally grow into adults.
Diseases Caused by Aschelminthes
Aschelminthes may cause the following diseases in humans
(i) Ascaris lumbricoides or giant intestinal roundworm is an
endoparasite of the small intestine of humans. It causes
ascariasis.
(ii) Wuchereria (filaria) or filarial worm is an endoparasite
in the lymphatic vessels and lymph nodes of humans. It
causes elephantiasis in the legs, arms, scrotum, etc.
(iii) Ancyclostoma duodenale or hookworm is an
endoparasite in the small intestine of humans. It
causes ancylostomiosis disease.