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LARVAL FORMS OF ECHINODERMS :- Echinoderm larva is strikingly bilaterally symmetrical in marked contrast to radially symmetrical adult. It swims about by means of a ciliated band, which may be complicated by a number of short or long slender projection or arms from the body wall. Based upon the nature and position of the arms or their absence, lame of different classes of Echinodermata may distinguished.

LARVAL FORMS OF MOLLUSCA :- Molluscan life histories do not perfectly correspond with taxonomy, but in general it is true that the archaeogastropods and the bivalves begin life as a trochophore and rapidly pass on to a veliger. There are different types of molluscan larvae according to the importance of the pelegic phase and amount of planktonic food taken. G. Thorson (1950) recognised three ecological types of larvae in Mollusca.

LARVAL FORMS OF CRUSTACEA :- Crustaceans show both direct and indirect development. In direct development (e.g„ Palaemon, crayfish), the adult is attained by progressive growth and differentiation of the embryo, so that the newly hatched young resembles the parents in general structure.

LARVAL FORMS OF TREMATODA, CESTODA AND ANNELIDA :- The trematods or flukes are either external or internal parasites, the cestodes or tap worms are internal parasites. The termatoda class includes three order . The fasciola hepatica which is an example of order digenea have mainly 5 larval forms (i) miracidium (ii) sporocyst (ii) redia (iv) Cercaria (v) metacercaria.

Nervous system in mollusca has a well developed nervous system. It also bears paired ganglia, nerves and connectives. One important aspect is there that a Circumentric ring is formed by ganglia. A pair of cerebral ganglia (masses of nerve cell bodies) innervate the head, mouth, and associated sense organs. NERVOUS SYSTEM IN MOLLUSCA​

NERVOUS SYSTEM IN ARTHROPODA​ is as advance as in Annelida. There is dorsal brain again connected with nerve ring to ventrae nerve cord. The arthropod nervous system consists of a dorsal brain and a ventral, ganglionated longitudinal nerve cord (primitively paired) from which lateral nerves extend in each segment.

The advanced nervous system in annelids is generally compare with coelenterates. The well developed nervous system can be seen here in form of a pair of cerebral ganglia (brain) and a double ventral nerve cord. This ventral nerve cord bears ganglia and lateral nerve in each segment as annelids are true segmented animals.

NERVOUS SYSTEM OF COELENTERATE AND ECHINODERM is not complex.  Hydra and jelly fish possesses diffused nervous system, diffused nervous system is most primitive form of nervous system. Nerve cells are distributed beneath the outer epidermis. Brain is absent though there can be concentrated neuron present locally and ganglia are present.

Regulation of osmotic pressure of an organism body fluid is refer to as osmoregulation. It allow to maintain balance of water content, fluid content and electrolytes. Hence due to osmoregulation body neither become too dilute nor become too concentrated. Right concentration of solute and amount of water must be maintain by any aquatic [fresh or marine] and terrestrial organisms. It can be mostly achieved by excretion.

EXCRETION IN HIGHER TERRESTRIAL INVERTEBRATES :- Excretory system regulates the amount of nitrogenous material, inorganic salts and water content in the blood. Both cockroach and earthworm are terrestrial in habitat their excretion is discuss in detail.

EXCRETION IN HIGHER AQUATIC INVERTEBRATES :- Process by which nitrogenous waste produce during metabolism is removed is known as excretion. Some animals such hydra, echinoderms and other may not posses proper excretory organs the reason is quite clear that they are aquatic and it is supposed that nitrogenous material may be diffuse out of there body through their body surface.

EXCRETION IN LOWER INVERTEBRATES :- Every organism possess different mechanisms, organs and different excretory product. For example porifera and hydra can perform excretion through body surface where as platyhelminthes possess a specialised cells known as flame cells.

ORGANS AND MECHANISM OF RESPIRATION IN HIGHER INVERTEBRATES :- There are generally three common ways through which invertebrates can perform the process  of respiration. These are cutaneous respiration which is mainly performed by lower invertebrates and annelids other is respiration through trachea and gills.

ORGANS AND MECHANISM OF RESPIRATION IN LOWER INVERTEBRATES :- In terms of biochemistry respiration is chemical reaction which occur in all living cell that provides energy after breakdown of glucose. Now respiration can be divided into two categories first aerobic respiration and other is anaerobic respiration.

PATTERN OF FEEDING AND DIGESTION IN HIGEHER INVERTEBRATES :- There are various mechanism for capturing and feeding over prey or food these are as follow Leeches generally feed over the fluid and soft tissue by piercing and then sucking from their host and simply absorbs the blood from the prey or host

PATTERN OF FEEDING AND DIGESTION IN LOWER INVERTEBRATES :- Every organism needs energy to perform its basic metabolic function. This energy can be obtain from food and sun. As sun is a universal source of energy but only autotrophic organism can obtain energy from sun.

The Ectoprocta are minute, sessile, colonial, unsegmented coelomate animals. Provided by the circular or cresentic lophophore, a u-shaped alimentary canal with anus opening near the mouth but outside of lophophore. Usually posses free swimming larva but without nephridia or circulatory system.

The Entoprocta or Endoprocta are group of small sessile aquatic animals. In which the body cavity is believed to be pseudocoel. They were formerly include in the phylum Bryozoa which however are true coelomate animals.

The Phoronida, brachiopod and Ectoprocta are collectively called as lophophorates coelomates because they all posses lophophore.

The word Rotifera is derived from latin meaning wheel barrier. They are commonly known as “wheel animalcules” as they are rotating wheel like structures

Hydrostatic movement occur when dominantly muscles are involved in their movement many organism show such kind of movement including Hydra, Earthworm, Leeches and Echinoderms.

LOCOMOTION IN PROTOZOA :- Moving ones body is an essential need of any organism. Some organism are sessile while other moves at very high speed. Some organisms moves very slowly such as amoeba or euglena where as other can move fastest example leopard.

The word coelom describes the body cavity that is internal space. But there can be difference in coelom true coelom will always be fluid filled lying between outer bodywall and inner digestive tube. It arises between two layers of embryonic mesoderm and consist of most of the visceral organs.

Metazoans can be define as multicellular organisms or as cellular animal or more accurately simply as animals.They are holozoic multicellular organisms.