Question

Describe the structure and life cycle of elphidium

Answer 1

Structure of Elphidium:

1. The shape of the animal is more or less round.

2. It is surrounded with a many-cham­bered, mullilocular and perforate calcareous shell consisting of 45 to 50 chambers.

3. The, chambers are boat-shaped and spirally arranged and each completely covers its predecessor. They communicate with each other through minute pores or foramen.

4. The margins of the shells are provided with’ peg-like projections. The shell bears a keel and the last chamber has a terminal aperture.

5. The chambers are filled up with cyto­plasm, which passes through the openings in the septa; the cytoplasm of the whole body of the animal is not divided into compartments but it is continuous. Nucleus may be one or many. The cytoplasm extends through the pores of the shell to form a layer over the shell.

6. Long, slender pseudopodia project outside through the minute pores present all over the shell and also through the terminal aperture; they often branch and anastomose with one another. Pseudopodia are of reticu­late type, i.e. narrow, almost thread-like, branched and continually anastomose.

7. The adult Elphidium is dimorphic, some are Schizonts or Agamonts, commonly known as microspheric individual, characterised by an initial central chamber or pro-loculus of relatively minute size, and some others are gamonts, more commonly known as macrospheric individual, which give rise to gametes, characterised by a large centrally placed chamber.

 



Life History of Elphidium:

Elplndium reproduces by both asexual and sexual modes. A well-marked alternation of generations is always present. The mode of reproduction in different species is not iden­tical.

The following description is applicable to Elphidium crispa (Fig. 18.7C-H):



Formation of macrospheric indi­viduals:

The microspheric form acts as a schizont or agamont which gives rise to the macrospheric form by a process of schizogony or multiple fission.

1. With the growth of the animal, the number of nuclei in the microspheric indi­vidual increases by division and gives off chromidia to the body protoplasm.

2. With the commencement of reproduc­tion the nuclei resolve into chromidia and the protoplasm leaves the shell, which is abandoned altogether.

3. The chromidia-laden protoplasm breaks up into a large number, about 200 amoeboid agametes or amoebulae or pseudopodiospores.

4. Each pseudopodiospore bears a num­ber of chromidial granules, which fuse to form a nucleus and secretes a single-chambered shell, the initial chamber of a macrospheric individual.

5. Each amoebula feeds, grows, secretes new chambers successively and becomes a macrospheric adult.

The life cycle of most trypanosomes species is digenetic. Man and domestic animals serve as primary host and blood-sucking insect, the tsetse fly serve as the intermediate host (fig. 9.23). Man and domestic animals becomes infected by the bite of tsetse fly. The injected parasite undergo prepatent period of active multiplication in lymph, intercellular spaces and tissue cells. Finally the parasite invades blood. It undergoes extensive multiplication.

During multiplication it changes shape of its body several times but finally changes into normal trypanosomes. At this stage, it is ready for transmission into the intermediate host. After sometime the pararits disappear completely from the blood due to formation of antibodies in host body. In pathogenic forms, the parasites invade vital organs from the blood causing serious disease.

In invertebrate host also, the parasite undergo extensive multiplication in stomach. Ultimately they migrate into salivary glands. When tsetse fly bites the skin of vertebrate host for its blood- meal, if pours a drop of saliva into the wound to prevent blood coagulation. With the drop of saliva numerous trypanosomes are inoculated into the blood of final host.