With extraordinary preservation, the bivalved Cassicaris clarksoni gen. et sp. nov. from the early Cambrian (Stage 3) Xiaoshiba Lagerstätte in Kunming, China, is characterised by having an anterior cardinal spine and a heavily segmented body, including an abdomen with a heavily sclerotised shell. Anatomically, the antennulae are small and the antennae are robust with seta-bearing podomeres, possibly of predatory function, followed by the other five pairs of biramous cephalic limbs. There are about 11 pairs of thorax segments, each corresponding to a pair of biramous limbs, including a multi-segmented endopod with feather-like podomeres and terminal spines, and a small paddle-shaped exopod fringed with setae. The bulbous, stalked eyes, which exhibit fineness of vision, infer adaptation to a vagile epibenthic lifestyle. Functionally, such assorted appendages may indicate an efficient suspension-feeding strategy for capturing tiny zooplankton. The median eye is presumably not a typical ocellar system but another compound eye, which may offer further insights into the evolution of compound eyes. Cladistic analysis implies that Cassicaris is a sister taxon to Pectocaris and Jugatacaris; these intriguing euarthropods are critical for discerning their body plan and living habits. Our findings offer fresh insights into the early evolution of Cambrian euarthropods, characterised by notable morphological disparity and ecological diversity. These fossils, including not only many intact individuals but also a few with well-preserved soft parts, form well-characterised groupings, making the broad pattern of Cambrian arthropod systematics increasingly consensual.

Appendage anatomy contributes crucial data for understanding the evolution and ecology of Euarthropoda. The Palaeozoic trilobites show a great diversity of exoskeletons in the fossil record. However, soft parts, especially appendages, have only been discovered from a few trilobite species. Here we report extraordinarily preserved appendages in the trilobite species Hongshiyanaspis yiliangensis Zhang & Lin in Zhang et al. 1980 (Redlichiida, Metadoxididae) from a single mudstone layer of the Xiazhuang fossil assemblage within the Hongjingshao Formation (Cambrian Series 2, Stage 3) near Kunming, Yunnan, SW China. The appendages exhibit the common architecture revealed by other trilobites and artiopods by consisting of a pair of uniramous antennae followed by a series of paired homonomous biramous limbs. The antennae in holaspid individuals comprise up to 27 spinous podomeres and their ontogeny occurs by lengthening of the podomeres. The post-antennal biramous limbs are similar to those in other polymerid trilobites and artiopods by having a single-segmented protopodite and an endopodite comprising seven segments, but possess a unique wide tripartite exopodite with long setae. Sophisticated appendage anatomy, including the body–limb junction, fine setae, putative muscle bundles and duct-type tissues, are also revealed. Appendages of trilobites, artiopods and other upper stem-group euarthropods are compared and summarized. The H. yiliangensis appendages highlight the high morphological disparity of exopodites and the conservativeness of endopodites in trilobites and artiopods. This morphological pattern, together with similar body patterning seen in crustaceans but not in chelicerates, supports the mandibulate affinities of trilobites and at least some artiopods.

The hibbertopteroid eurypterid genera Hibbertopterus, Dunsopterus, and Cyrtoctenus occur in the East Kirkton Limestone of Bathgate, West Lothian. Most specimens are fragmentary and appear to have been washed into the depositional area with plant debris and tuffaceous sediment. Nearly all of the identifiable material can be attributed to Hibbertopterus scouleri (Hibbert), but two isolated Cyrtoctenus combs, and a femur comparable with Dunsopterus have also been recognised.

New material of Hibbertopterus scouleri (Hibbert) reveals that the posterior legs and telson resemble those of the cyrtoctenids more closely than was previously thought. It is possible that Hibbertopterus, Dunsopterus, and Cyrtoctenus are indistinguishable except by relatively minor characteristics, and that all of the material from East Kirkton Quarry might be derived from a single eurypterid species. However, associations of the diagnostic sclerites which would demonstrate that these taxa are either cogeneric or distinct have not yet been found.