IVANOVIA TEBAGAENSIS WAS A CYATHIFORM PERMIAN CODIACEAN MEMBRANOUS ALGA WITH DIMORPHIC CORTICES

Species of Ivanovia (Codiaceae or Udoteaceae, Chlorophyta) have tradit ionally been characterized as phylloid or leaflike. Extraordinarily we ll preserved specimens of I. tebagaensis in limestone from the Upper P ermian of southern Tunisia indicate that the thallus was cyathiform or cup-shaped, similar to the broadly conical codiacean Calcipatera and to living Udotea cyathiformis. Ivanovia also shared with Calcipatera t he same general membrane structure consisting of bilateral cortices wi th palisades of utricles, now filled with micrite, and a medulla of tu bular coenocytes, now filled with sparry calcite mosaic. A cyathiform thallus would have had an inner and an outer cortex and those of I. te bagaensis were dimorphic. The utricular structure as usually seen in t hin sections using transmitted light is much clearer when viewed on po lished surfaces of hand specimens using reflected light. Commonly occu rring fused membranes suggest that the thalli reproduced vegetatively by budding. The complexity and regularity of the I. tebagaensis membra ne structure strongly suggest that a model which proposes that Ivanovi a is simply a diagenetic stage in the fossilization of the red alga, A rcheolithophyllum, is invalid.