Williriedellidae Dumitrică, 1970

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 : 117-119

Family Williriedellidae Dumitrică, 1970

Type genus. Williriedellus Dumitrică, 1970

Genus Hemicryptocapsa Tan, 1927 emend. Dumitrică1970

A rather similar morphology has the uppermost Tithonian-upper Hauterivian Syringocapsa agolarium Foreman, 1973 (Baumgartner et al., 1995, p. 543) that externally differs from Hemicryptocapsa capita (upper Valanginianlowermost Hauterivian) by only having a cylindro-conical apical horn of variable length and a similarly conical antapical one. Given this resemblance, the two species are regarded as congeneric, and S. agolarium should be transferred to Hemicryptocapsa . In this perspective, the Cretaceous species assigned by Dumitrică (1970) to Hemicryptocapsa should be, probably, transferred to Holocryptocapsa Tan Sin Hok, 1927 , or to another cryptocephalic genus. Taking into account the FAD of the two species one can suppose that H. capita originated in Syringocapsa agolarium Foreman during the Valanginian by the loss of the cephalic horn and of the distal spine. If this hypothesis is true, Hemicryptocapsa should belong to the family Syringocapsidae Foreman, 1973 or Eusyringiidae Steiger, 1992, rather than to the family Williriedellidae Dumitrică, 1970 .

O’Dogherty et al. (2017) emended also the diagnosis of this genus, reducing it to the tricyrtid species lacking nodose outer surface, the ornamentation of the shell surface being only represented by the regular pore frames. This is an idea with which we do not completely agree.

Text-fig 1. Inner mould of 3 specimens of Hemicryptocapsa capita Tan from a Valanginian sample of the Batain Plain, Oman, showing the inner structure of its skeleton. 1-3 lateral view, 4 apical view of specimen from fig. 1: c - cephalis, t - thorax, a - abdomen, pa - postabdomen, V - ventral side, D - dorsal side, Ll - left lateral side, Lr - right lateral side. On cephalis one can see the imprint of apical ray and, on thorax, the imprints of primary left lateral ray and primary right lateral ray .

Dimensions. Length of shell 152-246 µm, of cephalothorax outside abdomen 32-46 µm, of abdomen 86-180 µm, of postabdominal part 16-24 µm, diameter of abdomen 104-196 µm.

Remarks. The abundance of this species in the Sardinian samples allows knowing the variability of this species concerning both size and shape of the specimens or different segments of the shell. Fig. 3 shows only 5 specimens in order to demonstrate the morphological variability of the species concerning size of specimens, shape of cephalothorax and its superficial ornamentation, size and shape of the abdomen and postabdominal segment. The very small specimens ( Fig. 9c ) are very rare, most specimens having a big abdomen and well-marked constrictions between it and thorax and postcephalic segment. A similar specimen was illustrated by Matsuoka (1983, pl. 4, fig. 2) as Williriedellum sp. A .

Hemicryptocapsa capita resembles very much Syringocapsa agolarium Foreman, 1973 , by having the shell formed of three parts: a hemispherical cephalothorax partly included in the abdominal cavity, a large spherical abdomen without sutural pore, and a small inverted conical postabdominal segment. Briefly, one can suppose that this species could have its origin in the uppermost Tithonian to upper Hauterivian species Syringocapsa agolarium Foreman, 1973 (see Baumgartner et al., 1995, p. 542 for comparison), whose FAD precedes the FAD of H. capita , and from which it differs by only the loss of the apical and distal spines. Goričan ( 1994) illustrated three specimens of this species. We consider that the specimen illustrated on her pl.12, fig. 5, coming from a Hauterivian-Barremian sample, does not belong to this species because it is younger and has a different morphology: abdominal pores are much smaller and the last distal postabdominal segment has very small pores and a terminal spine. Also, the specimen with tuberculate abdomen illustrated by Baumgartner et al. (1995, p. 249, fig. 5) probably should not be included in this species. This morphotype seems to be a very short ranged Valanginian species occurring also in the Murguceva section from Svinița, Romania.

Range and occurrence. Upper Valanginian to lowermost Hauterivian, cosmopolitan and very abundant in the Valanginian.

Figures

Fig. 3 Stratigraphic log of the Valanginian succession in the S’Ozzastru section. Numbers refer to the sampled horizons.

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.