Phylum- Annelida, Arthropoda, Mollusca and Echinodermata
PHYLUM - ANNELIDA
Lamarck coined the term Annelida.Free living found in moist soil, fresh water, sea or few are parasite.Body is soft elongated, cylindrical or flattened divided into segments or metamers by ring like, groves called Annuli.
Symmetry - Bilateral, Germ layer - Triploblastic, Level of organisation - Organ-system level having tube within tube plan.Anterior end forms a distinct head with sense organ in few annelids.Appendages are simple, unjointed, and locomotory having Chitinous Setae and ParapodiaBody wall consist of
(1) Cuticle - Thin moist albuminoid cutical allow free exchange of gas.
(2) Epidermis - Single layered epidermis made up of supporting cell, sensory and glandular cell.
(3) Muscle layer - (a) Circular layer, (b) Longitudinal layer. Muscle are smooth/unstraited.
Body wall may have minute chitinous setae.
First Protostomi eucoelomate animals.Body cavity is true coelom lined by mesodermal coelomic epithelium. Schizocoel.It is divided by transverse septa into compartment.It is filled with coelomic fluid that contains cells.As such there is no skeleton. Fluid filled coelom serves as a hydrostatic skeleton.
Digestive tract is complete, straight and extends through entire body. The gut has both circular and longitudinal muscles. Few annelids are sanguivorous. Digestive gland are developed for the first time in Annelida.
Respiration is through skin i.e. Cutaneous respiration. Some have gills (branchial respiration).
Circulatory system is closed. Some blood vessels enlarge to act as pumping heart. (Heart appear first time in annelids)
The blood is red with haemoglobin dissolved in plasma (Erythrocruorin). It has amoeboid corpuscles only. Few Annelids like Seballa have Chlorocruorin as a respiratory pigment also. Hirudinaria has circulatory system with haemocoelic system.
Excretory organ is Nephridia. Coiled tubules also helps in osmoregulation.
(1) Ammonia in aquatic form
(2) Urea in land form
Nervous system consist of –
A circumenteric nerve ring, Double, midventral nerve cord with ganglia. Sence organ chemoreceptor, photoreceptor & tentacle, palp, eyes may be present.
Sexes may be separate or united. Asexual reproduction by budding' or fission in some cases also. Atoke (asexual), Epitoke (sexual) Phenomenon also found (Nereis).
Cleavage is spiral and determinate unqual & holoblastic.
Regeneration is usually found. Life history induds a trochophore larva in few Annelids.
Nereis: Inhabits in sea - shore between tide mark, burrows, Nocturnal, Carnivorous, Gregarious, Fertilization - in sea.
Parapodia in each segment except first & last.
During breeding body divides in two parts anterior asexual part - Atoke and posterior sexual portion Epitoke. This change is known as epitoky.

PHYLUM-ARTHROPODA
Arthropoda is the biggest phylum. About 9,00,000 species are there.
Von Siebold established phylum Arthropoda.
Arthopods are found in water, land, sea, in plant and animal. They are colonial, gregarious, shows parental care.
Sometime Parthenogenesis phenomenon also found i.e. Development of an unfertilized egg into an offspring.
Phylum incudes crabs, prawn, insects, spider, scorpian, ticks, mite, centipedes, millipedes. Fossil arthropoda are called Trilobites.
Body is Bilateral, Triploblastic with organ system level of organisation
Head is distinct [High degree of cephalization], Consists of many fused segments that bears well developed sense organ such as eyes, compound eyes, antennae.
Compound eye consists of many similar units ommatidia each having lens and capable of forming image.
Arthropoda have various shapes with externally segmented body. Segmention is either
a) Two, region with Head and trunk or Cephalothorax and abdomen
b) Three region with head, thorax & abdomen some or all segments bear jointed appendages. Hence name arthro joints, pod a - foot.
No internal segmentation like Annelida
PHYLUM - MOLLUSCA
It is second largest phylum.
Mollusca (Soft bodied) are marine, some are found in fresh water or on land.
Johnston coined the name-Mollusca.
Study of this phylum is known as Malacolog & study of shells of molluscan is know as Choncology.
Body is unsegmented with variety of shapes Neopilina is exceptionally segmented.
Molluscns are usually bilateral. Few are secondarily asymmetrical (snail) due to twisting (snail) during growth. These are triploblastic with system level.
Body wall includes one layered epidermis (usually ciliated) with unstriped muscles found in bundles.
Body parts consist of
(1) Head with sense organ. Head is absent in Pelecypoda & Scaphopoda.
(2) Dorsal visceral mass containing organ system.
(3) Ventral foot for locomotion.
(4) Thin fleshy fold or outgrowth of dorsal wall covers the body. This fold is called-man pallium. It encloses a space mantle or pallial cavity, between itself and 'the body.
The mantle usually secretes-an external limy shell.
Shell is made up of calcium carbonate and choncheolin protein.
Shell may also be internal (Cuttle fish), reduced and even absent (Octopus)
Coelom is greatly reduced. It is represented by cavities in the pericardium, kidneys and gonads. Space among the viscera contain blood and form haemocoel.
Digestive tract is complete. Buccal cavity contain a rasping organ the Radula, with" transverse row of teeth. Anus opens into the mantle cavity. Digestive glands are known as hepatopancreas.
Respiration is usually by gills i.e. Ctenidia are in the mantle cavity but respiration may takes place by body surface also. Dentalium respire by mantle. Pila respire by pulmonary sac on land and by gills in water.
Circulatory system is open. It includes dorsal pulsatile heart and a few arteries that open into sinuses. Cephalopoda has closed type of circulatory system
Blood has a copper containing, blue respiratory pigment Haemocyanin. Blood is colourless with amoebocytes.
Excretory system includes 1 or 2 pairs of sac like kidneys, which open into the mantle cavity. Kidney of molluscans are Metanephridia known as Kaber's organs or Organ of Bojanus. Excretory matter is ammonia or uric acid.
Nervous system comprises three paired ganglia
(1) Cerebral (above the mouth)
(2) Pedal (in the foot)
(3) Visceral (in visceral mass)
These are inter connected by
(1) Commissure (Joins similar ganglia)
(2) Connectives (Joins dissimilar ganglia)
Senses organ includes
(1) Eye - Present over a stalk called ommatophore (Gastropoda).
(2) Statocyst/Lithocyst - For equilibrium in foot
(3) Osphradia - Chemoreceptor/Olfactory as well as for testing chemical & physical nature of water.
Sexes usually separate (snail has ovotestis). Gonads have ducts. Fertilization may be external or internal. Cleavage is spiral, determinate, unequal and holoblastic.
Development is - Direct or indirect. Trochophore is very common larva of Mollusca phylum.
Larva: Glochidium (Fresh water mussel) and Veliger, (Pilo)
UNIQUE FEATURES
Precious pearl of the size of tennis- ball is made by a mollusc- Tridekna
"Nacre layer" is called "Mother of Pearl": This layer is made up of CaCO3 and choncheolin protetn.
Father of pearl industry - Koklchi Mikinimoto.
Molluscs are classified on the basis of shell, Foot, Nervous system and .Gills into seven classes.

UNIQUE FEATURES
- Thre body regions: head, visceral mass and foot.
- A glandular fold, the mantle, over the body,
- Mantle cavity with anal, excretory and genital apertures in it.
- Calcareous shell around the body in most cases.
- A rasping organ, the radula, in the buccal cavity.
- Much better sense organs, such as eyes, statocysts, osphradia, etc.
