Animal cells aren't all shaped the same way; the shape of a specific animal cell depends on its function and where it is in the body. Unlike plant cells, animal cells do not have rigid cell walls that limit them to a rectangular shape.
Many animal cells appear roughly spherical when viewed through a microscope. Neurons tend to have long protrusions sticking out from a central cell body. Adipose cells, which store fat in the body, tend to be almost perfectly spherical when filled, and become flatter when empty. Muscle cells are elongated, and they can stretch and contract when the organism moves.
The epithelial cells that make up the outer layer of skin tend to be flat and devoid of many of the organelles present in other cells, while the underlying layers of skin have cells that line up in columns or rows. Red blood cells are rounded, with a visible concavity in the center. Immune cells change their shape to squeeze into tight spaces between other cells and to stretch around invading bacteria, viruses and particles, surrounding and neutralizing them. Egg cells are typically large and round, while sperm cells have a rounded head and a tail that facilitates movement.