Syncytium

Syncytium is a living tissue where there are no  complete cell walls (plants) or cell membranes (animals). Syncytia have cytoplasm and many nuclei, but are not divided into separate cells.King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford. p435 

 Examples 
Fungal hyphae are often syncytia.
Lichen tissue may be syncytia with enclosed algal or bacterial cells.
Many insect eggs develop by nuclear division without cell membranes.
Skeletal muscles in vertebrates are syncytia: it allows rapid coordinated contraction of muscles along their entire length.
The placenta of mammals is a syncytium.

 References 

Category:Cell biology