CORYNOTRYPA FROM THE ORDOVICIAN OF NORTH-AMERICA - COLONY GROWTH IN APRIMITIVE STENOLAEMATE BRYOZOAN

Colonies of the runner-like bryozoans Corynotrypa delicatula (James) a nd C. inflata (Hall) are common encrusters of Middle and Upper Ordovic ian shells and hardgrounds, especially in Cincinnatian deposits. The s implicity of their zooids contrasts with complexities in the dynamics of colonial organization. Both species have uniserial branches that bi furcate at intervals and, in addition, give rise periodically to later al ramifications. Although angles of bifurcation and lateral ramificat ion each average about 80-degrees, bifurcations and lateral ramificati ons are fundamentally different modes of branch multiplication. In C. delicatula new lateral branches have conspicuous secondary zones of as togenetic change distinguished by elongation of successively budded zo oids. Unlike bifurcations, the first zooids in lateral branches in Cor ynotrypa are not linked to the parent branch by a narrow basal canal, and each new lateral branch can be regarded as a distinct subcolonial unit. The ancestrula, described here for the first time in an Ordovici an species of Corynotrypa, has a poorly differentiated protoecium and initiates a primary zone of astogenetic change. Colony growth in Coryn otrypa was more plastic than in many other bryozoan runners. The syste matics of C. delicatula and C. inflata are revised, and a lectotype is chosen for the former species.