Suttoniidae Schaaf

Dumitrica, Paulian, 2019, Cenozoic Spumellarian Radiolaria With Eccentric Microsphere, Acta Palaeontologica Romaniae 15 (1), pp. 39-60 : 40-41

Family Suttoniidae Schaaf , emend. Dumitrică 1983, reemended herein

Type genus. Suttonium Schaaf, 1976 , emend. Dumitrică, 1983

Emended diagnosis. Bilaterally symmetrical spumellarians with initial skeleton consisting of an eccentric microsphere with or without primary rays and a crescent-shaped deuteroconcha. Skeleton thin made usually of 2 parallel cortical lattice plates interconnected by short bars. Rays, when present, surrounded by a cortical shell forming three arms in the most evolved members.

Discussion. Before discussing the taxonomy of this family it is necessary a short history of the evolution of its meaning and its skeletal peculiarity.

The family Suttoniidae was erected by Schaaf (1976) on the basis of a peculiar specimen assigned to a new species and genus ( Suttonium praedicator Schaaf ) found in the Quaternary sediments from southwestern Pacific. He mentioned that this species has some similitudes with the spumellarian species Rhopalastrum? anumalum described by Sutton (1896) from the Eocene of Barbados, but he specified that the very good preservation of the specimen of his new species “does not permit any doubt (sic!): Suttonium praedicator must be assigned to the order Nassellaria ”. According to him, the microsphere represents the cephalis, the second shell the thorax, and the three arms the abdomen. According also to him, the two lateral arms are developed around the primary lateral rays (Lr and Ll) of the initial nassellarian spicule and the antapical arm around the dorsal (D) ray. What followed has proven how imprudent is to be completely certain in the science of life, especially when knowledge is incomplete and the study is superficial.

Dumitrică (1983) in a special study of the skeleton of the 3 species known in this genus showed that Suttonium is not at all a nassellarian genus, but a special spumellarian, as Sutton (1896) had suggested for the species he had described. It is a spumellarian that has the arms similar in structure to the arms of some Hagiastridae , from which it differs by the fact that in the course of its evolution the microsphere underwent a trend toward migration from the second chamber and the latter from the cortical three-rayed chamber suggesting a nassellarian skeleton.

The two new genera – Homunculodiscus and Parasuttonium – described below and that belong also to the family Suttoniidae allowed a better understanding of the history of this family and of its structural morphology. At present, when we know that the hagiastrids have a special type of microsphere, which is never spherical, and a pyloniacean mode of growth in their early ontogenetical stages (Dumitrica in De Wever et al., 2001), whereas the microsphere of Suttonium and of all Suttoniidae is a simple sphere, and shell growth is simple, it is difficult to sustain such a filiation. Consequently, despite the structural similarity of arms any relationship between Suttonium and the higumastrins is excluded.

Based on what we already know on the skeletal structure of the species of the genus Suttonium and on the structures of the new species and genera herein described we have now a general image of the initial and general structures of the members of this family.

The skeleton of the Suttoniidae consists of 2 parts: a diskshaped skeleton and a special initial structure. This initial structure consists, at its turn, of an eccentric spherical microsphere and a crescent-shaped attached chamber. By comparison with the initial stages of some foraminifers, I name this crescent-shaped second chamber deuteroconcha from the Greek deuter -, deuteron - second, secondary, and concha – shell. The side to which the deuteroconcha is attached to the microsphere is not casual. It is always attached to the side directed to the distalmost margin from the microsphere. To have an orientation of the shell of the genera with eccentric microsphere discussed in the present article, by comparison with the skeleton of Nassellaria I considered apical the part with the microsphere and antapical the part with the deuteroconcha. And because the two chambers (microsphere and deuteroconcha) are always together I prefer to name this structure diploconchal structure, from the Greek diplo – double and concha – shell. Microsphere is very small (about 13 μm) in the oldest species ( Homunculodiscus nascens nov. sp.) but can arrive to about 40 μm in the Quaternary species Suttonium praedicator Schaaf , when it is free from the constraints of a surrounding skeleton. The skeleton outside the diploconchal structure is usually a very flat disc formed, on both faces, by a porous cortical plate. The two faces of the disc are interconnected by short bars disposed irregularly or radially. These bars may be free or interconnected in the equatorial plane by bars parallel to the two faces. In optical view the perpendicular bars connecting the two faces appear as dark points and the horizontal bars interconnecting the perpendicular bars appear as less dark short lines. All this inner structure gives the shell a special ornamentation generally characteristic of species when looked in transmitted light.

The two new genera – Homunculodiscus Dumitrică and Parasuttonium Dumitrică obliged us to emend for the second time the diagnosis of this family to include in it not only species with 3 arms like the type genus but also genera with disc-shaped shell with or without arms because they have also an eccentric microsphere and a deuteroconcha

Range. Lower Paleocene to Recent and, generally, sparse.