ELPHIDIUM STRUCTURE & LIFE CYCLE Dr. P. RAVI SEKHAR LECTURER IN ZOOLOGY GOVT. COLLEGE FOR MEN (A) KADAPA
We know that snails and other molluscs have shells, but do you know some protozoans are also having shells? The most common shelled protozoans are foraminiferans belongs to the order foraminiferida (L., forare, pores + ferre, to bear). Almost all the members of the order are marine.
Their shells having many chambers and perforated all over with small pores, through which extend long and fine pseudopodia. Many foraminiferans exhibit the phenomenon of dimorphism (individual of a single species occurs in two distinct forms). Elphidium crispum (=Polystomella) is a typical example of the dimorphic forms.
ELPHIDIUM CRISPUM (POLYSTOMELLA)
Unicellular animal Hard translucent shell – calcium carbonate 90%, MgSo4, Si -10% Shell is Polythalamus or multilocular - several chambers
It also occurs in brackish waters. HABIT AND HABITAT Elphidium is a marine form, found abundantly on the bottom of the ocean. It is found creeping about on sea-weeds to a depth of 300 fathoms (one fathom =1.8 meters). It also occurs in brackish waters.
STRUCTURE OF ELPHIDIUM
ELPHIDIUM – TYPE STUDY DIMORPHISM: SHELL CYTOPLASM LOCOMOTION NUTRITION REPRODUCTION AND LIFE CYCLE
Dimorphism: Microspheric form: Megalospheric form: It occurs in two distinct forms the microsperic and megalospheric. Microspheric form: Proloculum is small in size. Many nuclei are present in the cytoplasm. It exhibits asexual reproduction. Megalospheric form: Proloculum is big in size. A single large nucleus is present in one of the chambers. It exhibits sexual reproduction.
DIFFERENCES BETWEEN MEGALOSPHERIC AND MICROSPHERIC FORMS
SHELL: Body is covered with a hard and translucent shell made up of calcium carbonate with small amounts of other inorganic compounds such as silica and magnesium sulphate. The shell is polythalamus or multilocular (many chambered) and perforated through cytoplasm becomes continuous from one chamber to another and also extends to out side to form pseudopodia. Initial single chamber - prolaculum. As animal grows in size, successive chambers are laid down in a spiral manner, forming whorls. Each chamber is larger than the preceeding one and each new whorl partially overlaps and conceals the older one. Thus, only the last whorl, which is the largest and most recently formed, is visible from out side. The over lapping portions of the chambers are refereed to as alar processes.
Cytoplasm: All the chambers of living E. Crispum filled with inner cytoplasm. Besides, a thin layer of cytoplasm covers the shell from outside, called outer cytoplasm. Endoplasm contains nucleus or nuclei, food particles, minute vacuoles, Golgi bodies, mitochondria, endoplasmic reticulum, ribosomes and brown granules or xanthosomes.
The reticulopodia are arranged in bundles around the shell. LOCOMOTION Elphidium creeps slowly on the sea bottom with the help of reticulopodia. The reticulopodia are arranged in bundles around the shell. With the contraction of distally placed bundles the body is pulled or dragged forward.
NUTRITION Nutrition is holozoic. The food consists mostly of diatoms and algae; it also captures other Protozoa and micro crustaceans. The mucus layer also contains proteolytic secretions help in paralyzing the prey and initiate the process of digestion even during capture. The captured food in a food vacuole and then the rhizopodia are withdrawn within the shell.
REPRODUCTION AND LIFE CYCLE Elphidium Life Cycle
Elphidium exhibits alternation of generation in its life cycle. Lister (1895) observed the development of the megalospheric form (sexual form) from the microspheric form (asexual form) by asexual reproduction. Thus megalospheric forms alternate with microsperic forms. There is always an alternation of asexual (microspheric) and sexual (megalospheric) generations in Elphidium. According to Jepps, the entire cycle of sexual and asexual phase is completed in about two years.
Elphidium – Asexual Reproduction The microspheric form reproduces asexually by fission to produce a number of amoebulae Nuclei creeps out of the shell and a small amount of cytoplasm collects around each nucleus. As a result, a large number of amoeboid cells (amoebulae) or agamates are formed. Detach from the parent cell and secrete initial chamber – proloculum Each amoebula secretes the proloculum, forms rhizopodia, then it grows and forms other chambers of the shell to become a megalospheric form.
Elphidium – Sexual Reproduction The megalospheric form reproduces sexually by syngamy or conjugation. The nucleus first breaks up into many small nuclei and the cytoplasm collects around each of these nuclei. The nuclei divide twice giving rise to a large number of tiny cells. The cells develop flagella and come out of the shell. The biflagellate cells are haploid and known as isogametes The isogametes are released into the surrounding sea water through the shell pores. The isogametes of two different individuals fuse (conjugate) in pairs to form zygotes. (The fusion of similar gametes is known as isogamy). The zygotes, thus, formed develop into microspheric forms. Each zygote secretes a shell around itself , new chambers are added
Life cycle The life cycle of Elphidium, clearly exhibits the phenomenon of alternation of asexual microspheric generation with sexual megalospheric generation.
when the elphidium die, their shells fall on the ocean floor like a steady rain and contribute to the formation of bottom sediments, called ‘ooze’.
Calcareous ooze is the general term for layers of muddy, calcium carbonate (CaCO3) bearing soft rock sediment on the seafloor. Investigating calcareous ooze of modern (i.e., Holocene) and ancient (e.g., Pleistocene) oceans means to elucidate the role that oceanic processes play in global climate change during various geologic time intervals and at different levels of precision
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