Hi:
There are a number of techniques I use depending on the habitat.

1st, I almost always have a pair of stainless steel tweezers with me.  I tuck
them neatly up the sleeve of my wet suite  (or in the custom pockets I had made
for them on my 3 mil skin) and as I poke around I can carefully pick up micros
or other mall shells in the crevices that I could not otherwise get.  That is
how I got 2 Pterynotus xenos in Honduras.

For storage of the shells… I have a small mesh bag made of no-see-um screen,
with a draw string at the top.  I keep it tucked inside my wet suite at the
neck line.  Then once I began using it, it is held on my left wrist with a
lanyard.

2nd – I buy inexpensive flat-oval pool nets.  The screen is fine enough for
most micros.  You can swim the grass with it at night.  It is amazing what is
on the grasses.  Simply dump it in a container when you get to the boat / shore
and sort later.  I have done the same on silt bottoms, and could probably do it
also on fine sand using it as a dredge.  I do not carry it very often.

For storage of the net while diving I usually stick it up inside my BCD in the
front.  It is sometimes a bit uncomfortable, but it beats dangling.  Someday I
will experiment with other ways to carry it, like Velcro & a snap connector on
a cord.  I usually use the net at the end of a dive for about 5 minutes before
I come up.

Leslie