Individual zooids, or separate members of a bryozoan colony, are very tiny, but the colonies may grow more than two feet in diameter. The shape of the colonies may, however, vary greatly in shape. Some branch upwards in a vertical manner while others may be flat and spread thinly over rocks or other plants. Most are found in marine environments, but one class of bryozoans, Phylactolaemata, exclusively inhabit fresh water bodies. Within this class is Pectinatella, a genus of bryozoans whose members often reside in North America. A relatively common species is P. magnifica, which grows larger than most other species, but has a less defined shape, appearing remarkably similar to a blob of jelly.