Structure of Polystomella (Elphidium)

Elphidium is a marine form. It is found creeping on Seaweeds to a depth of 300 fathoms.

• Phylum: Protozoa
• Class: Rhizopoda
• Order: Foraminifera

Structure

Elphidium also called Polystomella is a "dimorphic rhizopod". It is a unicellular microscopic protozoan, and 1 mm in diameter It is pale yellow in color. It lives in marine water. The body is covered by a shell. The shell is biconvex. The first formed chamber is the prolocutor. The surface contains spirally arranged V-shaped chambers. Hence it is called "poly thalamus or multilocular They overlap one another. These chambers show "openings" hence it is perforate Through these openings cytoplasm will come out. The cytoplasm is produced into a number of reticulopodia. which will form a network. From the hindered end of each chamber, cytoplasmic processes will develop. They are directed backward. They are called retral processes'.

The chambers are filled with cytoplasm.

1. The cytoplasm contains one or many nuclei.
2. The contractile vacuole is absent.
3. The mouth is absent.
4. Cytoplasm contains food vacuoles. They take up the process of digestion.

Dimorphism: Polystomella exhibits dimorphism. The individual occurs in two distinct forms.

1. Megalosperic form.
2. Microspheres form.

Megalospheric form:

Its prolocutor is big in size. A single large nucleus is present in one of the chambers. It takes up sexual reproduction.

Microspheres form:

Its prolocutor is small in size. Many nuclei are present in the cytoplasm. This form reproduces by asexual reproduction.

Locomotion and Nutrition: Polystomella shows slow creeping movements with the help of reticulopodia. It is a holozoic feeder. These Pseudopodia will capture the prey. When it comes in contact with the prey, it kills the prey by secreting toxic substances. The prey is digested in the food vacuole the cytoplasm absorbs the digested food.