Writing in the journal Zookeys, Jason Bond, director of the Auburn University Museum of Natural History, called the large find of new species of Aptostichus in the United States and particularly California "remarkable."
"California is known as what is characterized as a biodiversity hot spot. Although this designation is primarily based on plant diversity, the region is clearly very rich in its animal diversity as well," he said.
"While it is absolutely remarkable that a large number of species from such a heavily populated area have gone unnoticed, it clearly speaks volumes to how little we know of the biodiversity around us and that many more species on the planet await discovery."
Trapdoor spiders are rarely seen because they live in below-ground burrows covered by trapdoors made by the spider using mixtures of soil or plant material and silk.
The trapdoor serves to hide the spider when it forages for meals at the burrow entrance, usually at night, Bond said.
They are found in an amazing number of Californian habitats, he said, including coastal sand dunes, chaparral, desert, oak woodland forests and at high altitudes in the Sierra Nevada Mountains.
"Aptostichus to my mind represents a true adaptive radiation -- a classical situation in evolutionary biology where diversification, or speciation, has occurred such that a large number of species occupy a wide range of different habitats," he said.