Maris Otter is a barley variety. But when anyone in a brewing context says "Maris Otter" without any other explanation, they specifically mean "pale ale malt made from Maris Otter." That's implied. So tell your LHBS guy you want base malt, not crystal malt. Caramalt is a 10-15L crystal malt, kind of like a darker carapils. Maris Otter (pale ale malt) is a 3-5L base malt.