Here is my first Retiarus, which is a Foundry figure from GLAD1/4 Colosseum Champions. Foundry don't seem to give you tridents with your retiarus figures any more but I was lucky and got some off eBay. The retiarus (net fighter) was the only gladiator who habitually fought without a helmet and was armed with a trident, a net and, often, a dagger. His (or her) main opponent was the secutor (see my previous entry: http://legatuswargamesarmies.blogspot.com/2008/02/gladiator-secutor.html) but sometimes they are recorded as having fought murmillones whose helmets were, appropriately, decorated with a fish motif. Retiarii were unarmoured apart from an armguard (which this figure does not have) and, sometimes an armoured shoulder and neck plate on the left arm (galerus) which he does have. The wide belt was called a balteus.
This is a hoplomachus from the same Foundry pack as the retiarus. The quilted leggings are typical as is the (not visible in this picture) armoured armguard (manica) on the sword arm. The had small, round bronze shields and were usually paired against Murmillones or Thraces.