The isopods are mostly small marine crustaceans but include terrestrial sow bugs and pill bugs. Terrestrial forms live in moist soil and damp areas. Copepods are numerous small marine and freshwater planktonic crustaceans. The larvae of larger crustaceans may also be planktonic. Barnacles are sessile crustaceans with parts of their cuticle hardened into shells by calcium carbonate.
Barnacles feed by directing suspended particles toward the mouth with specialized appendages.
Phylum Echinodermata Most echinoderms are sessile or sedentary marine forms with radial symmetry as adults. Internal and external parts radiate from the center, often as five spokes. A thin skin covers a hard calcareous plate-like exoskeleton. Most have bumps and spines which serve various functions. A unique feature of Echinoderms is the water vascular system .