Marine Protozoa

Protozoans

Sub kingdom: protozoa of Kingdom Protista 31,250 species in 7 phyla Features: unicellular, freeliving or parasitic, mostly solitary though some colonial (ciliate and flagellates) move by pseudopodia, flagella, or cilia, some amoeba with tests,or shells, ciliates possess a mouth (cystostome) and nuclei of two sizes, reproduction mainly asexual, sexual reproduction in some groups.

Special marine ones... Subphylum Sarcodina (including amoeba) produce so-called pseudopodia-flowing extensions of the cell which can extend one or more at a time (depending what species) . Amoeboid marine protozoans, the Foraminiferans and Radiolarians build cases around themselves. Forams secrete a calcium (chalky) carbonate shell or test, which resembles a microscopic snail shell. Their pseudopod extend through pores to form a network used to trap diatoms and other minute organisms suspended in water. Most live on the bottom either free or attached. The covering of forams is potmarked with numerous holes which the pseudopods extend through to capture smaller ciliates and detritus. As these die, they sink to the ocean floor to form ooze which makes up thousands of square miles of the ocean floor. (white cliffs of Dover are foram tests). Scientists use the fossil tests to measure variations in the worlds temperatures as the structure and sizes of the tests change with water temp. changes. Forams living in cold water have fewer pores than those in warm water.

FORAMS ETC. There may be over 20,000 species of the order Forminiferia, which are characterized by forams having a rhizopodia and a one chambered or multi- chambered test that may be calcareous or siliceous with various substances such as sand or sponge spicules cemented together by pseudochitinous or gelatinous materials. They are among the largest protozoans with some reaching 100mm but usually .5 to 1.0 mm The tests are various shapes--oval, tubular, branched, spiral, etc. Most shells are multi chambered consisting of a series of successively larger chambers which are separated internally with pores or canals connecting them. The cytoplasm is found in all the chambers and is continuous through pores connecting the chambers. By passing though the pores of the test, the cytoplasm forms a layer (ectoplasm) over the test which connects to the endoplasm through the pores. As the animal grows it adds successive chambers to the initial chamber.

They capture their prey by means of their pseudopodal network which exhibits active streaming movements. They are found in marine and brackish water and only a few in fresh. A few are pelagic or sessile but most are creeping bottom dwellers (benthonic). A third of the ocean bottom is covered with Globigerina ooze, made mainly of the accumulation of the tests of this common foram. (usually in water under 4000 m deep because tests dissolve in the high concentration of CO2 in deep water.) Good fossils and important in detecting oil bearing strata.

(From Bio of Inverts Hickman Mosby Co ST Louis 1973)

Radiolaria (Subclass) Radiolarians form a glass like test composed of silica which is studded with long transparent spines to increase buoyancy and ward off predators. Typical shells are spheric with radiating spines though the structure varies...thin needlelike pseudopod capture food.

The radiolarians also form ooze, though radiolarian ooze and is usually found deeper being able to resist more pressure than the calcium carbonate foram tests.Radiolarian Web page

Ciliates are some of the protozoans that use cilia for locomotion. ..creeping over the bottom, living in gills, attached etc. The Tintinnids build their own quarters that drift in the water.

Reproduction is usually asexual binary fission whereby each effort results in two identical daughter cell (MITOSIS). This occurs when conditions are favorable...warm, lots of food etc.,. but sexual reproduction can occur in some when adverse conditions (drying up) occur as a survival method. The forams have alternation between sexual and asexual generations, having asexual reproduction to produce many organisms which secrete shells around themselves and when mature, they produce identical gametes which are liberated into the sea and fuse in pairs to produce individuals which in turn secrete a shell grow to maturity and repeat the cycle.

Life cycles are known for a few foraminiferans. They have two phases, one asexual and the other sexual. They are also dimorphic, having two types of individuals in each species, based mainly upon the size of the initial chamber (proloculm) of the test. The megalospheric type (gamont) has a large chamber (proloculum), one nucleus and is small in size while the microspheric type (schizont) has a small chamber, many nuclei and is relatively large. This is due to reproductive cycles which alternate between sexual and asexual generations.

Ecology Its complex as it would be for organisms found in every environment . They occur commonly in plankton...benthic communities, marine depths (13,000 ft for a foram) and since many protozoans exploit bacteria as a food source, they form part of the decomposer food web in nature. It is thought that they stimulate the rate of decomposition by bacteria by grazing on bacteria and keeping the bacteria community in a state of physiological youth and hence at the optimum level of efficiency. Ciliates can cause illness sees in some organisms.

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