Heymonsicambria

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Heymonsicambria is a Cambrian genus of small, crustacean-like animals called pentastomids found in the Orsten deposits of Sweden. It includes five species: H. kinnekullensis, H. scandica, H. repetskii, H. gossmannae, and H. taylori. The fossils range in size from about 0.47 to 0.71 millimeters long.

Most species have a flattened head with two pairs of head limbs on the underside. Kinnekullensis is incomplete, broken at the second body segment; the other three species have complete fossils.

All four complete species have a flattened head and ventral head limbs. H. repetskii is unusual because it has no visible trunk limbs, its head limbs are very small, and its head-limb sockets are fused to the trunk, showing more variation within the genus.

H. scandica is similar to kinnekullensis but has larger head-limb “fingers” and waisted body segments, while kinnekullensis is more tubular.

H. gossmannae has a low head, a rounded mouth area, and differently oriented head limbs.

H. kinnekullensis has a head about 2.4 times wider than it is long, a fairly hardened trunk, and small finger-like ends on the head limbs.

H. taylori is distinguished by the shape of its head limbs and the ratios of its trunk parts. It has partially fused limb sockets and weak limb segments, suggesting it sits between repetskii and the other species. Notably, H. taylori is also found in the earliest Ordovician of Canada, making it the youngest record of the genus and the only one outside Sweden.

This genus, like other Orsten pentastomids, is thought to be a larval stage, with the adult form not preserved.

Name origins: Heymonsicambria honors R. Heymons and reflects its Cambrian age. Kinnekullensis and scandica refer to Kinnekulle and Scandia (a historic region in southern Sweden). Repetskii honors John Repetski, gossmannae honors Annemarie Gossmann, and taylori honors John H. Taylor, who provided the specimens.