Rails Serializer: Custom attributes based on passed in options

animal_serializer.rb

class AnimalSerializer < ActiveModel::Serializer
  def initialize(object, options)
    if options[:type] == 'giraffe'
      self.class.attributes :skin_pattern, :leg_length
    else
      self.class.attributes :number_of_legs
    end
    super(object, options)
  end
  ...
end

AnimalSerializer.new(result, root: false, type: 'giraffe').as_json