(Atoms) Stars, Dust.
Spiral arms are parts of galaxies - both the galaxies and their spiral arms are huge, by our everyday standards. Spiral arms basically contain most of what the galaxies contain - including stars, dust, gas.
In spiral arms of spiral galaxies
Spiral galaxies are named for the (usually two armed) spiral structures that extend from the centre into the disk.The spiral arms are sites of ongoing star formation and are brighter than the surrounding disk because of the young, hot stars.See related link for a pictorial representation.
Arms of spiral galaxies.
Arms
Spiral galaxies have a clearly defined disk component characterized by spiral arms, while lenticular galaxies have a disk without prominent spiral arms. Irregular galaxies may also have a disk component, but it is usually less organized than in spiral galaxies.
Yes. Some spiral galaxies do contain at least 1 trillion stars.
They are called Spiral Galaxies or Barred Galaxies.
Yes, lenticular galaxies are lens-shaped. They will not have spiral arms.
Spiral galaxies and spiral means other body parts that stick out and move.
No. Elliptical galaxies are some of the oldest galaxies.They are also called early galaxies. The elliptical galaxies are made of low massed stars, a sparse interstellar medium and very low star forming characteristics.
That is a difficult question to fully answer as types of galaxies are not fully defined. A ball park figure would be dwarf galaxies, or spiral galaxies depending on the area in question. See related question for a full breakdown.