The job of the pivot table is to summarize your source data table based on the criteria you specify in the filter fields (Report Filter, Column Labels, and Row Labels). You can think of it as a very advanced way to arrange and filter your data.
The Limulidae are the only recent family of the order Xiphosura, and contain all four living species of horseshoe crabs: 1  Carcinoscorpius rotundicauda, the mangrove horseshoe crab, found in Southeast Asia. 2  Limulus polyphemus, the Atlantic horseshoe crab, found along the American Atlantic coast and in the Gulf of Mexico.
The closest relatives to the Limulus polyphemus are shown in this phylogenetic tree which is based on a morphological classification. All members in this tree are part of the family limulidae. Its closest relatives are the three other species of horseshoe crabs located in other areas in the world. I created both phylogenetic trees above referencing the information from http://www.ceoe.udel.edu/horseshoecrab/ and http://horseshoecrab.org/ as of April 10, 2011.