In this article we will discuss about Elphidium:- 1. Habit, Habitat and Structure of Elphidium 2. Nutrition in Elphidium 3. Reproduction.
Habit, Habitat and Structure of Elphidium:
Elphidium is a marine protozoa and is very common on the shore.
Structure of Elphidium:
Body of the Elphidium is covered with a perforated calcareous shell or crest and it looks more or less like an ammonite shell in miniature.
The shell consists of a number of chambers, arranged in a flat spiral and the surface of the shell is chiselled. Only the last whorl is visible from outside as each whorl is equitant, i.e., overlaps the previous whorl at the sides and hides it. The chambers are interconnected with each other through minute pores.
The outer whorl opens to the outside by a row of large pores. The chambers are filled with protoplasm which is granular in nature. A thin layer of protoplasm covers the outer-side of the shell. Pseudopodia are long, slender, often branched and come out from the pores of the shell as well as from the external layer of protoplasm (Fig. 10.25). The pseudopodia unite to form networks.
Elphidium is dimorphic and occurs in two forms, Megalospheric and Microspheric. The two forms are outwardly indistinguishable from each other but differ in internal organisation.
In megalospheric form the central chamber or initial chamber is large (megalosphere) and bears a large single nucleus while in the microspheric form the central chamber is small (microsphere) and contains many small nuclei. The preponderance of megalospheric forms is about thirty times more than that of the microspheric forms.
Nutrition in Elphidium:
Elphidium exhibits holozoic nutrition and feeds chiefly on diatoms, flagellates and unicellular algae. The pseudopodia are used in catching and entangling the food particles. The food entangled by the pseudopodia may be digested within the cytoplasm outside the test or it may be carried by the flowing cytoplasm to the chambers for digestion there.
Reproduction in Elphidium:
Elphidium represents an alternation of generation in its life history (Fig. 10.26). The megalospheric forms alternate with the microspheric forms. The microspheric forms always develop from zygotes. The microspheric forms give rise to megalospheric forms which in turn produce gametes. That means there is always an alternation of asexual and sexual generations.
The microspheric form divides asexually. The inner protoplasmic mass containing several nuclei creeps out of the shell and remains as a lump around it. A small amount of cytoplasm collects round each nucleus. As a result, a large number of small amoeboid cells are formed. Each of these cells develops into a megalospheric form.
During reproduction in megalospheric forms, the nucleus first breaks up into many small nuclei and the cytoplasm collects round each of these nuclei. The nuclei divide twice resulting into a large number of tiny cells.
The cells develop flagella and come out of the shell and conjugate in pairs (Isogamy, i.e., fusion of similar gametes). The zygote thus formed develops into microspheric forms. The first division of the zygote is, however, reductional. In some cases two megalospheric individuals are formed by direct fission of a megalospheric form.