Anno Faubel has written:

'Die Acoela (Turbellaria) eines Sandstrandes der Nordseeinsel Sylt' -- subject(s): Acoela, Platyhelminthes

The six types of Invertebrates are: Arthopods, Annelid Worms, Mollucs etc There could be five or seven types of invertebrates. The following are types of invertebrates: arthropods, cnidaria, echinoderms, mullusks, flatworms, roundworms, and segmented worms. Flat worms, roundworms, and segmented worms are could be grouped together, making seven types turn into five.