Figure 3.

Comparative musculature of Haootia quadriformis and the modern staurozoan Lucernaria: (A) bundles of muscle fibres of branching arms (a) extending into the calyx (c) of the holotype of H. quadriformis, which is raised slightly above the bedding plane, scale bar 1 cm; (B) detail of the muscle fibres of the arms (a) and calyx (c) of H. quadriformis, showing their flattened nature and preservation slightly above the ambient bedding plane; note the twisting and branching of the arm, and also the muscles at the base of the primary tentacle (pt), scale bar 1 cm; (C) detail of an arm of Lucernaria showing the longitudinal muscle fibres (lmf) and branching of the arm (a) (partly covered by gonads (g)), branches of the arm are tipped by secondary tentacles (st), scale bar 0.25 cm; (D) groups of muscles of H. quadriformis showing the interlacing of one set of muscle fibres with the ends of the fibres from the opposite side of the calyx, forming an irregular vertical seam (arrowed) between the two groups of muscles (orange), and a second set of muscles (purple) meet the muscles of the opposing side of the calyx at its base, scale bar 1 cm; (E) musculature of the calyx of the extant staurozoan Manania showing the manner in which the longitudinal muscles of the arms (blue) meet to define the shape of the calyx in a manner similar to that seen in Haootia (after [91]); (F) musculature of the calyx of the extant staurozoan Haliclystus, showing the more open nature of the calyx with the longitudinal muscles of the arms (blue) not meeting at the margin of the calyx as inferred for Mamsetia manunis gen et sp. nov. (after [91])—perradial musculature (red) is not seen in Mamsetia. All scale bars 1 cm.