Archaeodictyomitra dienii Dumitrică, 2022

Dumitrica, Paulian, Dieni, Iginio & Massari, Francesco, 2022, Valanginian Radiolarians Of Ne Sardinia (Italy) In The Frame Of The Weissert Event, Acta Palaeontologica Romaniae 18 (2), pp. 97-159 : 136

Archaeodictyomitra dienii Dumitrică nov. sp.

Figs. 13n, t

Description. Shell long subcylindrical to subconical consisting of four or five relatively long segments with slightly convex outline and separated by very weakly marked constrictions. Cephalis probably very thin-walled, its top not preserved in the studied specimens. Its base has the surface with 9 costae visible on half a diameter. Collar boundary well marked by a sudden widening of the thorax. Thorax difficult to separate externally from abdomen and abdomen from postabdominal segment. In fact, the number of post cephalic segments is difficult to establish because they are separated by very weakly marked constrictions. It seems that there are only two constrictions in the post cephalic portion of the skeleton, this signifying that there are only three post cephalic segments. Irrespective of their number, the test increases very slowly in diameter from cephalis to the distal end, which is slightly constricted. Costae very well marked and continuous from the base of thorax to the distal end of the test. Intercostal space has a single row of very small pores, usually elliptical and irregularly spaced. Distal end of test irregular, with costae not prolonged or very slightly prolonged beyond the intercostal areas.

Studied material. Two almost identical specimens.

Holotype. Figure 13n , coll. MGP-PD, stub PD120 - OZ838- R04-07 .

Paratype. Figure 13t , coll. MGP-PD, stub PD120 - OZ836- R08-11 .

Dimensions. Maximum length preserved (without cephalis) 185-200 μm, maximum diameter of test 80 μm.

Etymology. The species is dedicated to Dr. Iginio Dieni for his contribution to the knowledge of the geology of eastern Sardinia.

Remarks. Based on the two specimens one can suppose that this species has a rather constant morphology. By its general morphology, Archaeodictyomitra dienii n. sp.

resembles the very variable and probably polyphyletic Albian to basal Turonian species Dictyomitra montisserei (Squinabol, 1903) as emended by O’Dogherty ( 1994). Despite this resemblance, its absence in the fossil record of the Hauterivian to Aptian stratigraphic interval suggests that it is an independent species and probably the forerunner of Dictyomitra montisserei .

Occurrence. Rare in OZ838, late Valanginian, Sardinia, Italy.

Figures

Fig. 13 a, b - Apiaromitra apiarium (Rüst): a - OZ836, b - OZ839, a1 - detail of ornamentation of last segment, b1 - detail of ornamentation of penultimate segment. c - Archaeodictyomitra robustovum Dumitrică n. sp., OZ837. d - Archaeodictyomitra sp., OZ839. e, f - Archaeodictyomitra mitra Dumitrică: e - OZ838, f - OZ824. g-k - Archaeodictyomitra massarii Dumitrică n. sp.: g - OZ834, g1 - detail of surface x1000. h - OZ834, i - OZ839, j - OZ834, k - OZ839; k1 - detail of wall showing the cavernous structure, k2 - detail of surface. l, p - Archaeodictyomitra longipora Dumitrică n. sp., OZ836; l - portion of surface of p much magnified showing the elevated intercostal area. m - Apiaromitra tyaughtonensis (Cordey), OZ837. n, t - Archaeodictyomitra dienii Dumitrică n. sp.: n - OZ836, t - OZ837. o - Thanarla cf. pulchra (Squinabol), OZ824. r - Archaeodictyomitra judae Dumitrica n. sp., OZ839. s - Archaeodictyomitra humerosa Dumitrică n. sp., OZ839. Figs. a, b x250, k1 and k2 x450, all the others x300.