1) Living fossil 
Protulophila is a genus of symbiotic or commensal colonial Hydrozoa, known from very small hydroids. These marine hydroids live in the shelly tubes of serpulid tube worms, which are annelids. The genus Protulophila was named by Rovereto in 1901, from fossil material. For many years scientists knew these animals only from fossils, and the genus was...