Plasmodesmata are extremely small strands of cytoplasm. These tiny strands extend between adjacent cells through pores in the walls enabling transport and communication between them.
The cell wall of plant is not fully complete around the cell as it is interrupted by narrow pores carrying minute strands of cytoplasm. These fine strands interlinking the contents of the cells are called plasmodesmata (singular: plasmodesma). They form a protoplasmic continuum called symplast.
Plasmodesmata serve as a passage for fluids and dissolved substances to pass through. The translocation of ions, sugars, amino acids etc. occurs through the plasmodesmata.
Since animal cells have no walls lack plasmodesmata