Arcanicapsa simplicissima, 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 : 117

Arcanicapsa (?) simplicissima Dumitrică n. sp.

Figs. 9k, k 1

2017 Crococapsa tansinhoki (Hull) – O’Dogherty et al., p. 39, fig. 8.46,?8.47.

Description. Shell probably tetracyrtid with a pointed apical part and a globular distal part. Conical apical part consists probably of cephalis, thorax and abdomen. Cephalis conical imperforate except a circular pore with slightly protruding rim, well visible in the Fig. 9k 1 . Thorax and, probably, abdomen, in case of a tetracyrtid shell, truncated conical with irregularly distributed small pores which increase in size distally. Collar boundary not marked by a change in outline. Last segment globular, thick-walled, with circular or subcircular pores of irregular size and arrangement, and polygonally framed on the surface. It is armed with very few short three-bladed spines of irregular positions. Lumbar or postlumbar boundary, in case of a tetracyrtid shell, could be supposed in the place where there is a rapid increase in the size of pores and the shell has a concave outline due to the rapid increase in diameter. Distal end without an evident aperture but with a small central pore surrounded by a rosette of 6 small pores of variable shapes and sizes (fig. 9k1).

Studied material. A single specimen in sample OZ836.

Holotype. Fig. 9k , coll. MGP-PD, stub PD120 -OZ836- R07-18 .

Dimensions. Length 147 µm, diameter of last segment 113 µm.

Etymology. From Latin, superlative form of simplex = the simplest.

Remarks. This species, of which we have only the illustrated specimen, seems to be related to Sethocapsa leiostraca Foreman, 1973 , S. trachyostraca Foreman, 1973 , and other Tithonian and Lower Cretaceous taxa assigned before to the genus Sethocapsa , from which the new species differs by its smaller size, simple test with wide pores and absence of tuberculate or spiny last chamber. One of the specimens illustrated as Crococapsa tansinhoki (Hull) by O’Dogherty et al. (2017, fig. 8.46) resembles very well the specimen from Sardinia by having a very similar shape, pores of variable size and irregularly arranged, pointed apical part and intersegmental boundaries not marked outside by constrictions. The oth- er specimen illustrated under the same species by these authors (fig. 8.47) differs by having a rather arounded apical part, more regularly sized pores and intersegmentary boundaries marked by constriction. The only resemblance with our specimen concerns the presence of a rosette of distal pores.

Range and occurrence. Upper Valanginian of Sardinia, sample OZ836 .

Figures

Fig. 9 a, b - Eucyrtidiellum sardoum Dumitrică n. sp.: a, a1 - holotype, OZ836; b - paratype, OZ839. c-e, g - Hemicryptocapsa capita Tan: c - OZ838, d - OZ824, e - OZ837, g - OZ839. f-f2 - Gongylothorax oculoporus Dumitrică n. sp.: OZ824 and OZ826. h – Gongylothorax (?) sp., OZ834. i-i2 – Gongylothorax verbeeki (Tan), OZ824; i1, i2 - details of apical and apertural parts. j, j1, j2 - Williriedellum buekkense (Kozur), OZ824: j – lateral view, j1 – apical view with sutural pore, jb – distal view. k – Arcanicapsa simplicissima Dumitrică n. sp., OZ836, k1 – distal view showing the apical rosette. l-o, t, t1, u - Kozurium hindei (Tan): l, l1 - OZ837, m - OZ839, n - OZ834, o - OZ836, t-t1 x300, OZ825, n1 – distal aperture of fig. 9n. p-s1 - Cryptamphorella alieviana Dumitrică n. sp.: p, s - OZ825, r - OZ837, s1 detail of test of fig. s. Figs. p-s x200; figs. c-e, g x250; figs. a, a1, b, f, f2, h, h1, i, k-o, t, t1, x300; i1, i2, m x400.

Fig. 1 Geologic map of the Siniscola area, NE Sardinia (from Dieni & Massari, 1971, updated in 1986). Legend: a - Recent and present alluvial deposits (Holocene). b - Scree deposits (Würm-Holocene). c - Detrital cones mostly composed of gelifraction limestone clasts (“éboulis ordonnés”) (Würm-Holocene). d - Uncemented alluvial cones mostly consisting of limestone clasts (Würm-Holocene). e - Terraced alluvial deposits composed of clasts of basement rocks (Riss?). f - Tightly cemented and dismembered alluvial cones mostly made up of gelifraction limestone clasts (Riss?). g - Cuccuru ’e Flores Conglomerate: polymict, chaotic and thick-bedded breccia and stratified sandstone (middle Eocene). h - Siniscola Marl: grey and grey-yellow marl and, in the upper part, alternating marl/marly limestone with ammonites and very abundant radiolarians and sponge spicules (late Valanginian). i - Schiriddè Limestone: light-brown cherty limestone and limestone with marly interbeds, containing ammonites, radiolarians, sponge spicules and calpionellids (early Valanginian). j - Monte Bardia Limestone: thick-bedded to massive white limestone in places bioconstructed, with corals, nerineids, etc. (early Tithonian - late Berriasian). k - S’Adde Limestone: light-brown to grey fine-grained, well-bedded limestone, condensed with hardgrounds near the base, cherty in the upper part, with ammonites and belemnites in the uppermost part (latest Bathonian - earliest Tithonian). l - Dorgali Formation: well bedded quartz-arenitic and locally ooidal brown dolostone (middle-late Bathonian). m - Crystalline basement (phyllite, micaschist, paragneiss, quartzite, etc.) (Palaeozoic). n - Fault. o - Attitude of beds and schistosity planes. p - Limits of slumped masses of Jurassic formations (Quaternary). q - Concave-upward slip surfaces delimiting rotational slumps (Quaternary). r - Edge of fluvial terrace. s - Quarry. A-A’ Trace of the geological section of Fig. 2. (extracted from Bottini et al., 2018).