Homunculodiscus, Dumitrica, 2019

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

Genus Homunculodiscus nov. gen.

Type species. Stylodictya tainemplekta Caulet, 1991 .

Diagnosis. Test circular disc-shaped and very thin consisting of two parallel porous plates interconnected by short bars perpendicular to plates, most of them interconnected also in the equatorial plane of the disc by bars forming characteristic curved structures well visible in transmitted light. Pores circular, disposed commonly in radial rows and increasing slightly in diameter from the centre to periphery. Microsphere without primary radial spines. Deuteroconcha tending to reduce the lobes from three to one.

Remarks. This new genus differs from Stylodictya Ehrenberg , to which the type species was originally assigned ( Caulet, 1991), by having an eccentric microsphere, a diploconchal initial structure, no primary radial spines, and a different shell structure.

The diploconchal structure, and especially the deuteroconcha of this genus, shows a rapid and interesting evolution. In the earliest species ( Homunculodiscus nascens nov. sp., Fig. 1 , very early Paleocene) this chamber is very small and divided into 3 very small globular chambers. At younger levels of the early Paleocene ( Figs. 2 and 3 ) this chamber is better individualized and the number of chambers starts reducing. At last, in the middle Eocene species Homunculodiscus tainemplecta (Caulet) ( Fig. 3g and Fig. 4 ) this chamber is very well individualized, is larger than the microsphere and together with it makes a well characteristic body that suggests a homunculus, and that is well separated from the rest of the shell by a more or less disturbed oval circle.

Etymology. From the Latin homunculus – small man and discus – disc, due to the shape of the central shell of the type species. Masculine gender.

Range and occurrence. Lowermost Paleocene to lowermost Oligocene.

Figures

Fig. 1 a-g. Homunculodiscus nascens nov. gen., nov. sp. a-b – holotype; b, detail, double magnification of central part of fig. a; c-e – paratype 1, d-e detail of central part, double magnification of fig. c, focused at two levels. f-g. paratype 2; g – double magnification of central part of fig. f. a, c, DSDP 21-208-32CC, early Paleocene. f, DSDP-21-208-31CC, early Paleocene. Scale bars for a, b, c, f = 50 μm.

Fig. 2 a-h. Homunculodiscus cauleti nov. gen., nov. sp., DSDP 21-208-30CC; scale bars of figs. a-d = 50 μm, of figs. e-h same bars = 25 μm. e represents the central part of a; f represents the central part of b; g represents the central part of c; h represents the central part of d.

Fig. 3 a-d. Homunculodiscus tribulatus nov. gen., nov. sp., DSDP 21-208-30 CC; a, c – holotype; c – detail of central part of a, double magnified. b, d – paratype, d – central part of b double magnified. e, g – Homunculodiscus teinemplecta (Caulet), DSDP 21-207A-15CC; e – detail of central part of fig. g, double magnified. Fig. f, h - Cryptomanicula absconsa nov. gen., nov. sp. paratype; f – detail of surface of central part of fig. h, focused on surface, h focused on middle part, DSDP 21-208-30 CC. Scale bar for entire specimens = 50 μm.

Fig. 4 a-d - Homunculodiscus tainemplecta (Caulet), DSDP 21-207A-CC. Scale bar for all figures = 50 μm.