Homunculodiscus tainemplecta ( Caulet, 1991 )

Dumitrica, Paulian, 2019, Cenozoic Spumellarian Radiolaria With Eccentric Microsphere, Acta Palaeontologica Romaniae 15 (1), pp. 39-60 : 42-45

Homunculodiscus tainemplecta ( Caulet, 1991)

Figure 3e, 3g ; Figure 4 a-d.

1991 Stylodictya tainemplekta n. sp. – Caulet, p. 533, pl. 1, figs. 8, 9.

2005 Stylodictya tainemplecta Caulet. – Funakawa & Nishi, p. 218.

2015 Stylodictya tainemplekta Caulet. – Kamikuri, p. 148, pl. 18, fig. 6.

Description. Shell flat, very thin and circular, consisting of two perforated parallel cortical plates interconnected by very short bars perpendicular to the disc which, at their turn, are interconnected inside shell by bars in equatorial plane parallel to the disc forming a special inner ornamentation in optical view. Microsphere eccentric with very small and equal circular pores. Deuteroconcha larger than the microsphere, crescent-shaped and with pores sensibly larger than those of the microsphere. This diploconchal shell forms a characteristic homunculoid structure and is surrounded by a hallow-shaped circular or oval ring. This ring may be usually surrounded, at its turn, by a second, imperfect ring. The rest of the disc has an inner structure formed either by short curved ribbons or by punctiform connections between the two plates. Pores on all shell circular, dense, increasing in size distally and radially disposed especially outside the central part.

Dimensions. Diameter of shell 165-233 μm, of microsphere 13-14 μm, of deuteroconcha 21-37 μm, of first ring around the diploconchal structure 42-46/48-56 μm.

Remarks. The middle Eocene specimens from Lord Howe Rise are perfectly comparable with those from Kerguelen Plateau. The stratigraphic level of the FAD of this species is unknown because in both the samples from the Kerguelen Plateau and in those from the Lord Howe Rise, there are barren intervals or sedimentation gaps between the radiolarian bearing early Paleocene and middle Eocene sediments cored in the Lord Howe Rise holes 207A and 208 of the Deep Sea Drilling Project, Leg 21. For the same reason it is impossible to know the species from whom H. tainemplecta originated although H. cauletti nov. sp. seems to be a possible candidate as mentioned under H. cauleti nov. sp.

Range and occurrence: Middle Eocene or earlier to early Oligocene, Kerguelen Plateau ( Caulet, 1991); middle Eocene, SW Pacific, south Lord Howe Rise, DSDP 21- 207A-14 CC and 15 CC; middle-late Eocene transition from western North Atlantic and Antarctic oceanic area (Maud Rise). According to Funakawa & Nishi (2005) the last occurrence of this species is at 33.8-34 Ma, at the boundary between the late Eocene Eucyrtidium spinosum Zone and early Oligocene Eucyrtidium antiquum Zone in Southern Ocean (Maud Rise).

Figures

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.