The tough outer covering of Euglena, and Paramecium is called the Pellicle
This is called bark.
The external covering on arthropods is called the exoskeleton (or cuticle). It is made of a tough protein called chitin, a long chain polymer comparable to cellulose. Because it's inflexible, arthropods need to shed it (moult) in order to grow.
It is a shell, as in a cockle shell or oyster shell.
Yes. Arthropods are characterized by an exoskeleton made mostly from the tough protein chitin, also joint appendages and segmented bodies.
The exoskeleton is the hard outer shell of arthropods.
The external covering of an arthropod is referred to as an exoskeleton. In some arthropods (water varieties) the exoskeleton is composed mostly of calcium carbonate. In land varieties of arthropods, such as insects, their exoskeletons are made of a material know as chitin.