Fig. 7

Skeletal architecture of Labechia carbonaria in thin section. a Vertical section showing prominent thick long pillars (red arrow) and thin connecting cyst plates (yellow arrow) that are either flat, or slightly upwardly or downwardly curved. This thin section was cut slightly oblique to the vertical growth of the fossil, so the pillars are not cut perfectly vertically, but this does not prevent its easy recognition as a Labechia-form structure. Pillars are variably spaced in the structure but do not form alignments. Cyst plates are different lengths to achieve linkage between pillars. Growth layers are also visible as darker curved lines across the picture; b Transverse section showing pillars that have variable rounded shape in TS, some are amalgamated. The broad dense area, centre, is a slightly oblique TS through a growth layer, along which there is some recrystallisation of the structure. To the right of centre, pillar density is greater than the left. The left one-third of the picture is either stratigraphically above or below the right one-third and may be an indication of change in growth rate of the structure. a is sample number NHMUK PI S 10490$1; b is sample number NHMUK PI S 10491$1; both thin sections are labelled as having been made from the syntype and we presume these were cut from samples held by the BGS, possibly the paratype and holotype respectively, but this is unconfirmed. Photos taken by the authors