Amoebae that form slime moulds





Some single celled organisms, such as the

amoeba

, look like

wandering masses of slime (most are microscopic but the largest are

slime sheets up to over one metre across) but some

multicellular



creatures also build bodies out of slime. Indeed, this seems to be one

of the simplest multicellular body types and represents one of the most

ancient of Nature's experiments in multicellularity. Amoeba are not

bacteria, they belong to a group of protoctistans called the Protozoa

and resemble animal cells. However, even the much smaller and

genetically much simpler cells of bacteria can form multicellular slime

bodies!





Click here

for a more technical account of cellular slime moulds.





Most

amoebae

live as single-celled organisms in the water and soil, but

some amoebae can also form multicellular slime structures. Amoebae

are not bacteria, rather they are micro-organisms belonging to a group

called the Protoctista. Amoebal cells are typically 10-100 times the

diameter of bacterial cells and have the structure typical of animal

cells, but they are not animals because animals always form complex

multicellular bodies. Some amoebae (called myxamoebae), such as



Dictyostelium

, will live in the soil as single cells that feed and reproduce

for many generations, but if these cells start to run out of food in their

neighbourhood, then they send chemical signals to one another and

the amoebae respond by streaming in long conveys to a common

rendezvous. When they arrive, these amoebae do something very

strange, they form a

multicellular mound

or aggregate that piles on new

coming cells, getting taller and taller. Eventually the cells at the tip of

the mound form a nipple-like protuberance and this takes charge as it

is designed to become the 'head' of our new organism. All this happens

on a small scale, these mounds are only a few millimetres in diameter.

