An orthothecid hyolith with a digestive tract from the early Cambrian of Bornholm, Denmark

Figures & data

Figure 1. A. Maps showing the position of Bornholm relative to the Danish mainland. B. The island with major roads and communities. C. Area with the locality Vejrmøllegård at Læså rivulet near Aakirkeby and Grødby rivulet, exact collecting locality unknown. D. Geological map of southern Bornholm showing sedimentary units and the position of Vejrmøllegård relative to the Læså rivulet and Læså Formation. Geological map based on Graversen (2009).

Figure 2. Correlation between Siberian and Baltoscandian stages, acritarch zones and lithostratigraphic units on Bornholm. Modified from Moczydłowska & Vidal (1992) and Nielsen & Schovsbo (2011).

Figure 3. Circotheca johnstrupi (Holm, 1893). Specimen MGUH 31848 with preserved digestive tract. A. External mould with digestive tract removed. B. Specimen with digestive tract and anal tube in place. C. Latex cast of external mould. D. External mould showing external surface of operculum. E. Latex cast of external mould of operculum showing external surface of operculum. F. Ventral side of extracted digestive tract. G. Dorsal side of extracted digestive tract and anal tube. H. Posterior end of conch with septa. I. Detail of digestive tract in left ventral oblique view. J. Detail of digestive tract in right lateral view. Læså Formation at Vejrmøllegård, Læså rivulet. Collected by K.A. Grönwall. Scale bars = 0.1 cm.

Figure 4. Circotheca johnstrupi (Holm, 1893). Lectotype MGUH 1506. A. Partial steinkern and partial external mould in right oblique view. B. Reproduction of original figure in Holm (1893, pl. 1, Fig. 28). C. Right lateral view of latex cast of external mould. D. Detail of ornamentation. Line across the conch may mark possible shell breakage. Læså Formation at Vejrmøllegård, Læså rivulet. Collected by J.F. Johnstrup. Scale bars in A–C = 0.5 cm. Scale bar in D = 0.1 cm.

Figure 5. Circotheca johnstrupi (Holm, 1893). A. Paralectotype MGUH 1507, partial steinkern, left lateral view. White infilling on either side is old ‘latex’. B. Reproduction of original figure in Holm (1893, pl. 1, Fig. 30). C. Paralectotype MGUH 1514, partial steinkern in dorsal view with phosphatized bacterial matter along the centre and septa at the apex. D. Reproduction of original figure in Holm (1893, pl. 1, Fig. 71). Læså Formation at Vejrmøllegård, Læså rivulet. Collected by J.F. Johnstrup. Scale bars = 0.5 cm.

Figure 6. Circotheca johnstrupi (Holm, 1893). A, B. Steinkern of MGUH 1508 purportedly the original of Holm (1893, pl. 1, Fig. 31). C, D. Steinkern of MGUH 31849 proposed here as true original of Holm (1893, pl. 1, 31). E, F. Steinkern of MGUH 1509, original of Holm (1893, pl. 1, Fig. 32). Læså Formation at Vejrmøllegård, Læså rivulet. Collected by J.F. Johnstrup. Scale bars in A, B, D = 0.5 cm. Scale bars in C, E = 0.1 cm.

Figure 7. Orthothecid? MGUH 1510. A. Internal surface of supposed operculum. B. Enlarged reproduction of original figure in Holm (1893, pl. 1, Fig. 33). Læså Formation at Vejrmøllegård, Læså rivulet. Collected by J.F. Johnstrup. Scale bar = 0.1 cm.

Figure 8. Circotheca johnstrupi (Holm, 1893). A, E. MGUH 31850. External mould with bacterial mat near operculum and internal surface of operculum. B, F. MGUH 31851. External mould with impressions of ornamentation and external surface of operculum. C, D, G. MGUH 31852. External mould, latex cast of external mould and external surface of operculum. H. MGUH 31853. Operculum showing external surface. Læså Formation at Vejrmøllegård, Læså rivulet. Collected by J.F. Johnstrup. Scale bars in = 0.5 cm.

Figure 9. Circotheca johnstrupi (Holm, 1893). A, B. MGUH 31854, latex cast of ventral side of external mould showing well-preserved ornamentation. Læså Formation at Grødby rivulet. Collected by J.F. Johnstrup. C, D. MGUH 31855. Dorsal, left lateral and ventral views of latex cast of external mould showing well-preserved ornamentation. Scale bar in A = 0.5 cm. Scale bars in B–E = 0.1 cm.

Figure 10. Circotheca johnstrupi (Holm, 1893). A, B. MGUH 31856. Steinkern of conch in ventral and left lateral views with operculum resting on floor of conch with external side down. C. MGUH 31857. Ventral side of nearly complete conch. D. MGUH 31854. Detail of latex cast of conch showing two shell layers. See Fig. 9A for entire specimen. Scale bars in A, C = 0.5 cm. Scale bars in B, D = 0.1 cm.

Figure 11. Circotheca johnstrupi (Holm, 1893). A. MGUH 31850. Detail of phosphatized bacterial mesh below operculum. See Fig. 8A for entire specimen. B. MGUH 1514. Detail of posterior part of conch with phosphatized bacterial infilling. Numbers 1–3 indicate three possible shell layers. See Fig. 5C for entire specimen. Scale bars in = 0.1 cm.

Graversen, O., 2009: Structural analysis of superposed fault systems of the Bornholm horst block, Tornquist Zone, Denmark. Bulletin of the Geological Society of Denmark 57, 25–49.

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Moczydłowska, M. & Vidal, G., 1992: Phytoplankton from the Lower Cambrian Læså formation on Bornholm, Denmark: biostratigraphy and palaeoenvironmental constraints. Geological Magazine 129, 17–40.10.1017/S0016756800008104

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Nielsen, A.T. & Schovsbo, N.H., 2011: The Lower Cambrian of Scandinavia: depositional environment, sequence stratigraphy and palaeogeography. Earth Science Reviews 107, 207–310.10.1016/j.earscirev.2010.12.004

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Holm, G., 1893: Sveriges Kambrisk-Siluriska Hyolithidæ och Conulariidæ. Sveriges geologiska undersökning C 112, 1–172.

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