Hello! Athenian "marines" (Greek: epibatai) probably would have worn similar gear as the hoplites on land, since they belonged to the same property class (thus linen or bronze armor, a helmet, and a large shield). In fact, on a number of occasions our sources (e.g. Thucydides 1.49.1) explicitly refer to the deck-soldiers as hoplites, and these soldiers could be expected to serve on land if needed. I should point out that the Romans seem to have had an even less defined system for their "marines" (classiarii, "[men] of the fleet"), who were (at least during the Punic Wars) either infantrymen transferred temporarily to ships or oarsmen/sailors given weapons and armor; in this case, their title referred to their role rather than a specific occupation or branch of the military.