Blastulospongia sp.

Kouchinsky, Artem, Bengtson, Stefan, Landing, Ed, Steiner, Michael, Vendrasco, Michael & Ziegler, Karen, 2017, Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia, Acta Palaeontologica Polonica 62 (2), pp. 311-440 : 427-429

Blastulospongia sp.

Fig. 82A, B, SOM 3.

Material.—Two almost complete specimens, SMNH X6065 and 6066, and a single fragment from samples 1/22.5 and 1/26.3 (section 1, Fig. 4 ), Medvezhya Formation, western Anabar Uplift. Correlated with the lowermost Cambrian Stage 2.

Description.—Hollow spherical tests perforated with numerous rounded pores. The smaller specimen (Fig. 82A) is ca. 350 μm and the larger one (Fig. 82B) ca. 800 μm in diameter. The pores are 20–50 μm in diameter and randomly scattered on the surface with a density of 150 pores/mm 2. Thickness of the wall is 10–20 μm. Wall of the larger specimen is deformed with isometrical folds.

Remarks.— Blastulospongia sp. is represented by two specimens that are markedly different in diameter, although having the same density and diameter of pores. They are different from all known species of Blastulospongia in their diameter, pore sizes and pore density. Blastulospongia monothalamos from the middle Cambrian of Australia are 1.0–1.9 mm in diameter and with pores ca.50 μm in diameter. Blastulospongia mindyallica Bengtson, 1986 , from the upper Cambrian of Australia is 280–520 μm in diameter, with 15–20 μm perforations and a few μm-thick wall ( Bengtson 1986) and has ca. 300 pores/mm 2. Blastulospongia polytreta Conway Morris and Chen, 1990 , from the lower Cambrian of South China has a maximum diameter of 350– 370 μm and ca. 7 μm-thick walls with ca. 1500 pores/mm 2 that range in diameter from 9 to 21 μm ( Conway Morris and Chen 1990). Aetholicopalla adnata from Meishucunian Assemblage Zone 2 of South China (Yang et al. 2014: fig. 13P) is probably also a Blastulospongia that is similar to the form described herein. It is ca. 700 μm in diameter with pores larger than 50 μm. From the Fortunian strata of northwestern Canada, Pyle et al. (2006) reported two “indeterminate spheroids” 425 μm in diameter with pores from 3 to 10–15 μm in diameter and compared these to B. polytreta . Blastulospongia minima (nomen nudum) referred to as planktonic Sarcodina incertae sedis represents the main component (50–90%) of presumably lower–middle Atdabanian-age, pelagic bedded cherts in olistostome-containing flysch of the Spassky terrain (Russian Far East), where they co-occur with siliceous spicules (Panasenko 1998). Blastulospongia minima spherical tests are different from other species of Blastulospongia in being much smaller. They are reportedly 15–60 μm in diameter and are perforated by pores of 1 μm (in smaller specimens) to 3 μm (in larger ones) in diameter and may represent a protistan genus different from Blastulospongia .

Several fossils attributable to Blastulospongia were previously described from Siberia. A hemispherical problematicum, ca. 0.85 mm in diameter with pores 20–40 μm in diameter, is known from the lower Pestrotsvet Formation ( Spinulitheca billingsi Zone ) at the Gonam section on Mount 1291 m (sample 1605 of Val’kov 1987: pl. 14: 15). Irregularly spherical, rarely elongated fossils 1–2 mm in diameter with pores up to 0.5 mm in diameter (Khomentovsky et al. 1990: 34, but up to 40 μm in diameter in the illustrations) from the upper Kessyusa Formation on the Olenyok Uplift (i.e., on the Kyursyuke River ca. 17 km upstream of the mouth) (12 specimens; Khomentovsky et al. 1990: pl. 6: 5–7, pl. 7: 1) and from the lowermost Pestrotsvet Formation at the Aldan River at Byukteleekh (single specimen; Khomentovsky et al. 1990: pl. 7: 2) were referred to as Blastulospongia monothalamos . A globula from the lower Emyaksin Formation at the Udzha River reported as Markuelia sp. by Vasil’eva (1998: pl. 44: 10) is ca. 0.55 mm in diameter with pores up to 30 μm in diameter.

Deformation of the wall in the larger specimen suggests that it was not completely mineralized in life but rather contained a significant amount of organic material. Pickett and Jell (1983) first suggested a sphinctozoan or foraminiferan affinity of Blastulospongia . A radiolarian affinity of Blastulospongia was discussed by Bengtson (1986) and White (1986). It was also regarded as a problematicum variously assigned to the sponges, radiolarians or uncertain protists ( Conway Morris and Chen 1990). A protozoan affinity may be supported by a silicified and supposedly agglutinated nature of the tests studied herein, in which energy-dispersive X-ray analyses suggest the presence of detrital minerals incorporated into the wall and cemented with silica. The wall consists of 1–10 μm crystals having the following elemental composition: O (60–75 atomic %), Si (ca 10–25 atomic %), K (2–10 atomic %), Al (2–10 atomic %) with trace amounts of Fe, Mg, and Ca (SOM 3). Co-occurrence with calcitic shelly fossils (now dissolved) preserved as phosphatic internal moulds as well as with organophosphatic Fomitchella sclerites and siliceous/agglutinated Platysolenites (SOM 3b) is compatible with an originally siliceous composition of the Blastulospongia wall (SOM 3a), rather than reflecting selective replacement by silica during diagenesis. The wall of Platysolenites antiquissimus consists of up to 5 μm crystals displaying the same elemental composition (SOM 3).

Based on these results, Blastulospongia is herein interpreted as a silicified and probably agglutinating organism similar in composition to Platysolenites . They may represent unilocular tests of benthic or semi-bentic foraminiferans. Some were probably sessile because of the flattened hemispherical shape and evidence of attachment (i.e., B. polytreta from the Shuijingtuo Formation; see Conway Morris and Chen 1990: fig. 4.5, 4.6).

Stratigraphic and geographic range.— Blastulospongia is originally known from the middle and upper Cambrian of Australia (Pickett and Jell 1983; Bengtson 1986). It was subsequently reported from the Terreneuvian Series of South China ( Conway Morris and Chen 1990), Siberia (Val’kov 1987; Khomentovsky et al. 1990; Vasil’eva 1998), and Laurentia (Pyle et al. 2006).

Figures

Fig. 4. The δ13Ccurve for Kotuj River section 1and sampled horizons with fossiliferous samples (arrows with numbers). Shift in stratigraphic column carb at Nemakit-Daldyn–Medvezhya formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 4, Bemella jacutica?; 8, Anabarella plana; 9, Watsonella crosbyi; 10, Pseudoyangtzespira selindeica; 11, Aldanella crassa; 13, Aldanella attleborensis; 15, Philoxenella spiralis; 16, Barskovia hemisymmetrica; 18, Khairkhania cf. evoluta; 19, Ceratoconus striatus; 21, Salanyella cf. costulata; 23, Purella cristata; 25, Yunnanopleura sp.; 26, Obscurania auriculata; 29, Protoconus cf. crestatus; 32, Siphogonuchites triangularis; 34, Lopochites sp.; 37, first appearance of Halkieria sp.; 39, first appearance of Chancelloria sp.; 40, Tianzhushanella sp.; 42, Khetatheca cotuiensis; 46, Turcutheca sp.; 48, Orthothecid operculum type A; 52, Fomitchella infundibuliformis; 57, Hyolithellus sp.; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 71, Anabarites hexasulcatus; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus; 77, Blastulospongia sp.