from “Wikipedia”

<==o Sorberacea
   `--o Aspiraculata
      `--o Hexacrobylidae
         |--o Gasterascidia
         |  |-- C. lyra Monniot C. & Monniot F., 1973
         |  `-- C. sandersi Monniot C. & Monniot F., 1968
         |--o Hexadactylus
         |  |-- H. arcticus (Hartmeyer, 1923)
         |  |-- H. eunuchus (Monniot F. & Monniot C., 1976)
         |  `-- H. ledanoisi (Monniot F. & Monniot C., 1990)
         |--o Oligotrema
         |  |-- O. lyra
         |  `-- O. psammites
         `--o Sorbera
            |-- S. unigonas Monniot C. & Monniot F., 1974
            `-- S. digonas

Reference(s):

Special thanks to:

Jos H. M. Dols, for gathering information and species of these animals.