Boreskov

PP‐42HOLLOW SPINES IN RADIOLARIAN SKELETONS AND SPONGE SPICULESAfanasieva M.S.*, Amon E.O.***Borissiak Paleontological Institute RAS, Moscow, Russia**Zavaritsky Institute of Geology and Geochemistry, Uralian Branch of RAS,Ekaterinburg, RussiaThe shape of main spines in radiolarian skeletons is very diversiform. In overwhelmingmajority the main spines are solid: rodlike, conical or faceted; rarer meet hollow spines.Spines frequently serve as a simple prop for axopodia; but in the inner channel of hollowspines or inside various microtubes can stretch axopodial filaments or bunches of axopods.The texture of hollow main spines and other hollow skeletal structures is variant. Certainhollow spines and internal spicules represent the simple tubes (pl. 1, figs. 1‐4, 6, 7, 8, 9).Other hollow spines and crossbeams are sectioned by horizontal lamellar septum (pl. 1, figs.14, 15). Several hollow spines are complicated with development of special inner capsules(pl. 1, figs. 10, 13) which are supported precisely on the center of spine by radial lamellarseptum (pl. 1, figs. 5, 10‐13, 16, 17), quite often dual (pl. 1, figs. 5, 10). Capsules are hollow(pl. 1, figs. 10). If they are solid (pl. 1, figs. 13), it is most likely a secondary phenomenon.Wall thickness of capsule is comparable to wall thickness of hollow spine, or somewhat less(pl. 1, figs. 10). Internal surface of hollow spine smooth, but internal and external surfaces ofcapsules rough, with small tubercles and ledges (pl. 1, figs. 10, 13). Functional purpose ofsuch capsules not clearly. Probably, they could be as a part of the hydrostatic apparatus.The morphology of initial spicules and spiny radiolarians resemble sponge spicules.However, main difference between radiolarian skeleton and Porifera spicules consists is inpeculiarities of skeleton formation: radiolarians spines grow spirally (pl. 1, figs. 18, 19),whereas spicules of sponges grow away from the center (pl. 1, figs. 20, 21).Radiolarian hollow spines and other hollow skeletal structures, especially spines withhollow capsules, meet extremely rare in fossil state. Only twenty species with various hollowskeletal elements of all classes of radiolarians from Ordovician, Devonian, Carboniferous,Cretaceous and Paleogene are presented in our collection. Probably, subcylindrical spineswith hollow internal channel are the initial, most ancient and primitive structures, whichhave originated in Cambrian. However, the further development of skeletons went on a wayof formation of faceted solid spines. This was the optimal form, provides the greateststrength of spines in the least amount of a mineral material. Nevertheless, themorphogenesis of subcylindrical hollow spines repeated many times during all Phanerozoicup to the present.The study was supported by the Program of Presidium of RAS "Origin of Biosphere and Evolution of Geo‐Biological Systems" and the Russian Foundation for Basic Research, project no. 10‐04‐00143.208