FORMULA FOR CALCULATING CONCENTRATION OF PLANT EXTRACTS

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GENERAL CHARACTERS OF RADIATA

SUPERPHYLUM RADIATA

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The radiata is a superphylum which includes both the echinoderms, cnidarians and ctenophores and is not part of the usual classification system and is not used by the biologists. The group includes radially symmetric animals of Eumetazoa[1]. The echinoderms, however, are members of the Bilateria, because they exhibit bilateral symmetry in their developing stages. Their radial symmetry is secondary.

In 1983 Thomas defined a sub-kingdom called Radiata Consisting of the phyla porifera, myxozoa, placozoa, cnidaria and ctenophore (that is, all the animals that are not in bilateria). The five kingdom classification of Lynn Margulis and K. V. Schwartz keeps only Cnidaria and Ctenophora in Radiata.

We will deal hear with the Cnidaria and Ctenophora with respect to their general characters.

COELENTRATA (OR CNIDARIA)

The cnidarians[2] are an aquatic group of organisms, commonly known as hydroids, jellyfish, sea anemone and corals. They are tentacle bearing, radial or biradial animals with sac-like body composed of two basic cell layers. The inner layer of cells, called the gastrodermis, lines the hollow space, the coelenterons, which functions in digestion and transport and into which there is single opening, the mouth. The outer cell layer consists of an epidermis. The gastrodermis and epidermis are separated by a thin, acellular matrix or mesolamella or by a jelly-like material containing cells called the mesoglea or mesenchyme.

All Cnidaria are constructed from eight basic cell types – epithelial, muscular, nervous, glandular, reproductive, interstitial, mesenchyme and cnidoblasts. Cnidoblasts are most frequently present on tentacles and contain stinging structures – the nematocysts which function in defence and in the capture of food; all cnidarians are carnivorous in habit.

All cnidarians have tissue level of organization having, epiderma, nervous, digestive and muscular tissues, but lacking specialized organ system. Fundamentally two body forms are repre: Polyp and Medusa (we will talk about these later)

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EXTERNAL MORPHOLOGY

Coelenterates are a acoelomate and radially symmetrical lower invertebrates (Radiata). The coelenterates are represented by two morphologically different types of individuals, polyps and medusa.

Polyps are sessile with a tubular body (eg. Hydra, Metridium (Sea anemone))

Medusa are free swimming umbrella or bell-shaped body.

Some coelenterates pass through both stages in their life cycle with an alternation of generations.

INTERNAL STRUCTURE

Internal structure of Cnidarians can be understood by studying the histology of Hydra.

GASTROVASCULAR CAVITY

Almost all cnidarians have a central cavity called coelenterons, functionally referred to as gastrovascular cavity. It has only one opening – the mouth. There is no anus and no excretory pore. The undigested food and wastes exit the cavity through the mouth opening.

BODY WALL

There body wall is composed of two layers of cells, outer layer is called epidermis and the inner layer is called gastrodermis/endodermis. The two layers are separated from each other by a thin delicate, non-cellular gelatinous layer called mesoglea or supporting lamella.

1. EPIDERMIS

The epidermis is composed of small, more or less cuboidal cell. It is a protective and sensory layer. The epidermis is covered externally by a thin coating of cuticle. It has various types of cells as follows.

a. Epithelio-muscle cells

Most of epidermis is composed of epithelio-muscle cells that helps in both muscular contraction and epithelial covering. The epithelial part extends up to body surface and the basal muscular part is drawn out into two muscle processes along the longitudinal axis. Muscle process contains contractile fibril, the myoneme.

b. Gland cells

These are tall cells found chiefly on pedal disc and around mouth region. These secrete a mucus-like sticky material which serves for attachment and protection.

c. Interstitial cells

They are present in the interstitial spaces between epithelio-muscle cells. They are small round undifferentiated cells and are capable of developing any other kind of cells, such as reproductive, glandular, stinging etc.

d. Cnidoblasts

Many of the interstitial cells of epidermis develop into specialized cells called cnidoblasts. These are specially present on the tentacles arranged in clusters or batteries. They are oval shaped cells with basal nucleus and possess a sac-like organoid – the nematocyst. It is like a capsule enclosing a coiled tube or thread.

e. Sensory cells

They occur scattered throughout the epidermis among epithelio-muscle cells and are specially found on tentacles, hypostome and pedal disc.

f. Nerve cells

Throughout the evolutionary trend, true nerve cells or ganglion cell occurs for first time in coelenterates. They are derived from interstitial cells of epidermis. They occur at the base of epithelio-muscle cells just above their muscle processes..

g. Germ cells

During summer, interstitial cells of some regions of body, divide repeatedly and proliferate like reproductive cells forming gonads, which later differentiate into testes and ovaries.

2. GASTRODERMIS

The coelenterons is internally lined by gastrodermis. It is formed chiefly of large, columnar cells. This layer is mainly nutritive in function. The gastrodermis is composed of following types of cells.

a. Endothelio-muscle or nutritive cells

These are most abundant cells forming bulk of gastrodermis. These resemble the epithelio-muscle cells of epidermis except that their basal contractile processes are single, more delicate and oriented at right angles to the processes of the epithelio-muscle cells. There contraction reduces the diameter of the body and tentacles, which becomes narrower and longer.

The free end may bear two whip-like flagella and blunt pseudopodia like projections. The movement of flagella keeps the food in the coelenterons in motion. The pseudopodia like projections can engulf food particles.

b. Endothelial-gland cells

They are smaller than nutritive cells and occurs scattered among nutritive cells. They lack muscle tails at basal end, but may bear one or two flagella. The gland cells are absent in the tentacles. They are of two types.

· Enzymatic gland cells: secrete digestive enzymes into gastrovascular cavity for extracellular digestion.

· Mucous gland cells: secrete a slimy fluid serving as lubricants.

c. Interstitial cells

A few interstitial cells occur between the bases of nutritive cells. These are totipotent cells and thus can transform into all other type of cells.

d. Sensory cells

Sensory cells are found in between nutritive cells. They are supposed to be stimulated on entry of prey into gastrovascular cavity.

e. Nerve cells

These are similar to those present in epidermis, except that they are present here in fewer no. than epidermis.

3. MESOGLEA

It is non-cellular thin layer secreted by both epidermis and endodermis and separates the epidermis and gastrodermis. It serves for attachment of cellular layers.

 

TO BE CONTD…..

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[1] Eumetazoa is a clade which includes all major animal phyla 

Technorati Tags: CNIDARIA,RADIATA,CTENOPHORA

except sponges.

[2] Cnidos, thread; Gk