Hexactinellida Schmidt, 1870

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 501

Class Hexactinellida Schmidt, 1870 Order and family uncertain

Pentactines with a long acanthose ray

Fig. 70M, N, Q.

Material.—Several tens of spicules total, from samples 3/44, 3/49, 3/49.5, 3/50, 6/39.1, 6/41.7, 7/33, 7/34, 7/34.7, 7/34.8, and hundreds, including SMNH Sp 10301–10303 from sample 7/36.7. Emyaksin Formation, Malaya Kuonamka and Bol’shaya Kuonamka rivers; correlated with the Delgadella anabara Zone, Atdabanian Stage. One, from sample 6/0.3; Emyaksin Formation, Bol’shaya Kuonamka; correlated with the lower Dokidocyathus regularis Zone, Tommotian Stage.

Description.—Siliceous spicules composed of five rays containing axial canals. One of the rays is much longer, sometimes curves distally (Fig. 70M), and is covered with low, irregularly situated, and longitudinally extended tubercles. The ray can be somewhat swollen at the base (Fig. 70N), but commonly only slightly reduced in diameter distally from its base. Four other rays taper gently at 60–120° to each other in plan view and are inclined at 20–30° away from that plane, perpendicular to the base of the longer ray. The rays are covered with less distinct and smaller tubercles.

Remarks.—The specimens described herein are most similar to those illustrated by Fedorov in Shabanov et al. (1987: pl. 35: 6) and by Vasil’eva (1998: pl. 24: 2) from the Atdabanian Stage, upper Emyaksin Formation, southeastern flanks of the Anabar Uplift and to those reported by Kouchinsky et al. (2011: fig. 40N–Q) from Stage 5 beds of the Malaya Kuonamka River. The tubercles probably represent weathered distally directed barbs similar to those described from some pentacts and hexacts of Cambrian hexactinellids ( Rigby 1975; Bengtson 1986b: fig. 8; Bengtson et al. 1990: fig. 15A–F). Similar spicules, but preserved in carbonate surrounded by organic sheaths are reported from the lower Cambrian Forteau Formation of Newfoundland ( Harvey 2010).