Ichthyostraca is a class of parasitic

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s. It is composed of two subclasses;

Pentastomida The Pentastomida are an enigmatic group of parasitic arthropods commonly known as tongue worms due to the resemblance of the species of the genus ''Linguatula'' to a vertebrate tongue; molecular studies point to them being highly derived crust ...

and Branchiura. They mainly parasitize various vertebrates and feed on their blood or mucus.

References

{{Taxonbar, from=Q22986461 Arthropod classes Maxillopoda Crustaceans Parasitic crustaceans