The Collaborative International Dictionary of English v.0.48:

Cirrostomi \Cir`ros"to*mi\, n. pl. [NL., fr. E. cirrus + Gr. ?
   mouth.] (Zool.)
   The lowest group of vertebrates; -- so called from the cirri
   around the mouth; the Leptocardia. See Amphioxus.
   [1913 Webster]