Microarchitecture of Body Wall of Extant Cyclostome Ectoprocts

Scanning electron microscope and light microscope studies of the body wall in cyclostome stenolaemate ectoprocts show that this wall has a distinctive microarchitecture. The microstructures consist of a linear series of longitudinal canals in the central region. Adjoining regions on either side have laminae of overlapping calcareous tablets. In some cyclostomes at certain stages of growth, laminae may show a less orderly meshwork pattern near the canals. The laminate layers of calcareous tablets are enclosed in an organic matrix and are penetrated by tubuli which pass from the inner part of the body wall to the canals and also link the canals. The canals with organic and mineralized matrices open into pores in the body wall. This elaborate meshwork and canal and pore system provide the framework for growth and resorption of the body wall and facilitate transport of cellular materials from one zooid to another in a colony. Calcification at the distal part of a colony seems to proceed in a series of stages around sites of calcification. The pattern of the body wall of the cyclostome ectoproct does not parallel a molluscan pattern of skeletal growth as previously proposed. The hypothesis of a hypostegal coelom in some cyclostome ectoprocts is rejected.