As you probably know from your research, diatoms
can be classified by their shape as either
'centric' (round) or 'pennate' (mostly they look
like ovals). As it turns out, the round centric
diatoms appeared first in the fossil record,
meaning that they are more primitive. Over
geological time, the diatoms evolved into pennate
forms. In general, you are correct and most
centric diatoms cannot move. However, some centric
diatoms can move and some pennates cannot!
How do the diatoms which can move do so?
Scientists think that these diatoms secrete a sort
of mucus and slide along a surface on that. It is
possible that they also retract this mucus as they
move. Pennate diatoms have developed a special
slit in their silica shells called a 'raphe'
through which the mucus is secreted. This
structure is also important in classifying
diatoms, or telling one pennate species from
How do the moving diatoms move?Do they have
flagella or something to move them around? I
didn't know that only round diatoms could move,
but I don't know much about diatoms. Diatoms live
free in the ocean, don't they? So do the diatoms
that can't move still get pushed around by the
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