Chitin-encapsulated bodies, resistant to freezing and a limited amount of desiccation. They serve as a special means of asexual reproduction in the Phylactolaemata, a class of fresh-water Bryozoa. They are 0.01–0.06 in. (0.26–1.5 mm) long, and their shape and structure are important to the taxonomy of the group.
Statoblasts are classified as follows: sessoblasts, those which attach to zooecial tubes (structures of the outer layer or zooecial of an individual in the colony) or the substratum; floatoblasts and spinoblasts, both of which have a float of “air” cells and therefore are free-floating; and piptoblasts, which are free but have no float (see illustration).
sessoblast of Fredericella sultana. (d) Sessoblast of Stolella indica.">
Some types of statoblasts. (a) Spinoblast of Pectinatella magnifica. (b) Floatoblast of Plumatella repens. (c) Piptoblast or sessoblast of Fredericella sultana. (d) Sessoblast of Stolella indica.
These bodies are produced in enormous quantities from spring to autumn. They develop by organization of masses of peritoneal cells and epidermal cells that bulge into the coelom. Each mass then secretes protective upper and lower chitinous valves, the rims of which often project peripherally. Statoblasts are therefore somewhat disk-shaped.
These bodies remain dormant for variable periods of time and serve to tide species over adverse ecological conditions, such as freezing or drying, which kill the colony. During this time they may be dispersed over considerable distances, being carried by animals, floating vegetation, or the action of water currents. When environmental conditions become favorable, which is usually in the spring, statoblasts germinate and a zooid develops from the mass of cells lying between the two valves. Statoblasts of Lophopodella have germinated after 50 months of drying. See also Bryozoa.
