Carnets de Géologie [Notebooks on Geology] - Article 2012/03 ( CG2012_A03 ) 39 I nconsistencies in proposed annelid affinities of early biomineralized organism Cloudina (Ediacaran): structural and ontogenetic evidences Olev V INN 1 Micha ł Z ATOŃ 2 Abstract: Cloudina, an important Ediacaran index fossil, is considered as one of the earliest biominera- lizing organisms. Its biological affinities have not been fully resolved and phylogenetic links with both annelids and cnidarians have traditionally been suggested. Differences in tube morphology, ultra- structure and biomineralization suggest that Cloudina is not closely related to any recent skeletal anne- lid ( e.g. , serpulids, sabellids and cirratulids) and their skeletons are not homologous. The way of asexual reproduction in Cloudina resembles more that of cnidarians. The presence of a closed tube ori- gin (base) in Cloudina is also compatible with the hypothesis of an animal of cnidarian grade. Key Words: Cloudina; Annelida; Serpulidae; Cnidaria; Ediacaran; biomineralization. Citation: VINN O. & ZATOŃ M. (2012).- Inconsistencies in proposed annelid affinities of early biominera- lized organism Cloudina (Ediacaran): structural and ontogenetic evidences.- Carnets de Géologie [Note- books on Geology] , Brest, Article 2012/03 ( CG2012_A03 ), p. 39-47. Résumé : Incohérences dans les affinités supposées de l'organisme primitif biominéralisé Cloudina (Ediacaran) avec les annélides : preuves relevant de la structure et du développe- ment ontogénétique.- Cloudina, un important fossile édiacarien, est considéré comme l'un des pre- miers organismes biomineralisés. Ses affinités biologiques n'ont pas encore été entièrement élucidées : des relations phylogénétiques avec les annélides et les cnidaires sont habituellement envisagées. Des différences dans la morphologie, l'ultrastructure et la biominéralisation du tube suggèrent que Cloudina ne puisse être étroitement apparentée à aucun squelette d'annélides actuelles, qu'il s'agisse de serpu- lidés, de sabellidés ou de cirratulidés ; leurs squelettes ne sont pas homologues. Le mode de repro- duction asexuée de Cloudina ressemble davantage à celui des cnidaires. De plus, la configuration fer- mée de la partie initiale (proximale) du tube chez Cloudina est compatible avec l'hypothèse d'un animal de la catégorie des cnidaires. Mots-Clefs : Cloudina ; Annelida ; Serpulidae ; Cnidaria ; Édiacarien ; biominéralisation. 1 Department of Geology, University of Tartu, Ravila 14A, EE-50411 Tartu (Estonia) Olev.Vinn@ut.ee 2 Faculty of Earth Sciences, University of Silesia, Będzi ńska 60, PL-41-200 Sosnowiec (Poland) mzaton@us.edu.pl Manuscript online since March 12, 2012 [Editor: Christian EMI G] 1. I ntroduction Cloudina is a tube-building metazoan orga- nism of problematic affinities that widely occurs in deposits of the terminal Neoproterozoic Edia- caran Period (GRANT, 1990), between 549 ± 1 Ma and 542 ± 1 Ma (GROTZI NGER et al. , 1995; AMTHOR et al. , 2003). Two distinct species are recognized, C. hartmannae GERMS, 1972, and C. carinata CORTI JO et al. , 2010, while rest of species could be junior synonyms of C. hart- mannae (CORTI JO et al. , 2010). It is significant for being among the precursors of biologically controlled mineralization and being an impor- tant Ediacaran index fossil (HUA et al. , 2005). The geochemical data suggest that Cloudina formed originally aragonitic skeleton (CALLOW & BRASI ER, 2005), however, relatively little is known about the biology of Cloudina. There is a record of drilling predation upon Cloudina (BENGTSON & YUE, 1992; HUA et al. , 2003). Follo- wed from the location of predatory drill holes, Cloudina organism was presumably able to pro- tect its shell nearest to the aperture and its soft body may have been located in the upper, growing portion of the tube (HUA et al. , 2003). According to traditional point of view, Clou- dina was closely related to annelids and espe- cially to serpulids (GERMS, 1972; GLAESSNER, 1976). However, HAHN & PFLUG (1985) and CON- WAY MORRI S et al. (1990) did not support GERM's and GLAESSNER's proposed relationships, and classified Cloudina just in its own family, Clou- dinidae. The occurrence of dichotomous bran- ching in C. hartmannae, which implies asexual reproduction led GRANT (1990) to classify Clou- dina as a coral-like cnidarian. Recently, dichoto- mous branching has also been found in C. cari- nata CORTI JO et al. , 2010, from the Ediacaran of Spain (CORTI JO et al. , 2010). In contrary, as a result of their thorough review on biology of Cloudina, HUA et al. (2005) found that Clou- dina's morphology, skeletogenesis, and asexual reproduction are broadly similar to modern