Acta Palaeontologica Polonica No. 3-4 1983 [antikvár]

ADAM URBANEKTHE SIGNIFICANCE OF GRAPTOBLASTS IN THE LIFE CYCLE OF CRUSTOID GRAPTOLITESURBANEK, A.: The significane of graptoblasts in the life cycle of crustoid graptolites. Acta Palaeont. Polonica, 28, 34, 313326, 1983 (issued 1984).Graptoblasts are small ovoid bodies with a flat lower, and a convex upper, wall, the latter provided with a costulation having a fusellar aspect. First found as isolated bodies associated with graptolite remains, graptoblasts were later recognized as a constituent of crustoid colonies (Kozlowski 1949, 1962). Their biological role remains largely enigmatic. The view that graptoblasts were formed within the authothecae is rejected and a conclusion is advanced that graptoblasts were closed, resting terminal portions of the stolothecae, housing encysted dormant zooids. They may be compared with the resting terminal zooids in Rhabdopleura and with the hibernacula of ctenostome bryozoans. Graptoblasts provided an adaptation allowing the species to survive the periods of adverse conditions when the rest of the colony disintegrated. One could hypothesize that after germination the graptoblasts produced small propagules ejected through a narrow cryptopyle and forming new colonies after they settled on the substrate.Key words: Graptoblasts, Graptolithina, Crustoidea, dormancy, germination, propagules, life cycle.Adam Urbanek, Zaklad Paleobiologii, Polska Akademia Nauk, Pracownia Grapto-litow, ul. Newelska 6, 01-447 Warszawa, Poland. Received: April 1980.ESSENTIAL DATA ON GRAPTOBLASTSGraptoblasts are small, ovoid or vesicular bodies, with flat lower and convex upper walls, made of organic material and described by Kozlowski (1949) as a provisional group of fossils in some way related to graptolites or pterobranchs (fig. 1). This preliminary conclusion was convincingly confirmed in his later studies (Kozlowski 1962). He established that graptoblasts found in situ are intimately associated with the colonies of the Crustoidea. These observations which solved in general the problem of the morphological nature of graptoblasts have recently been completed by a rather detailed analysis of their micromorphoiogy and ultrastructure (Urbanek and Rickards 1974; Urbanek, Mierzejewski and Rickards, in press). Yet, in spite of a considerable growth of know-