How to convert to VertexId in Spark/Scala Graphx?

Question

I am trying to create a graph in Apache Spark Graphx using Scala. My code so far is:

    import org.apache.spark._
    import org.apache.spark.graphx._

    case class EdgesCl(Source:Long, Destination:Long, SourceLayer:Long, DestLayer:Long, Weight:Int = 1)

    object actual
    {

      def parseEdgesCl(str: String): EdgesCl =
      {
        val line = str.split(",")
        EdgesCl(line(0).toLong, line(1).toLong, line(2).toLong, line(3).toLong)
      }

      def main(args:Array[String]) {
        val conf = new SparkConf().setMaster("local").setAppName("SparkCommunityDetection")
        val sc = new SparkContext(conf)

        //Create RDD with Network data
        val textRDD = sc.textFile("/home/input_Files/test_net.csv")

        val EdgesClRDD = textRDD.map(parseEdgesCl).cache()

        val nodes = EdgesClRDD.map(node => (node.Source, node.SourceLayer)).distinct
        nodes.take(1)

        val edges_lines = EdgesClRDD.map(edge => ((edge.Source, edge.Destination), edge.SourceLayer, edge.DestLayer))

        // Defining a default vertex called nowhere
        val noedge = "noedge"

        val edges = edges_lines.map { case ((source, dest), s_layer, d_layer) => Edge(source, dest, s_layer) }

       //Defining the Graph
       val graph = Graph(nodes, edges, noedge)
       }
     }

I get the following error:

Error:(67, 23) type mismatch;
 found   : org.apache.spark.rdd.RDD[(Long, Long)]
 required: org.apache.spark.rdd.RDD[(org.apache.spark.graphx.VertexId, Any)]
Note: (Long, Long) <: (org.apache.spark.graphx.VertexId, Any), but class RDD is invariant in type T.
You may wish to define T as +T instead. (SLS 4.5)
Error occurred in an application involving default arguments.
val graph = Graph(nodes, edges, noedge)

How can I convert the "nodes" in the correct data type, so that I can make the graph?