Willwerathia

Size comparison of Willwerathia (A) and other synziphosurines.

As a synziphosurine, Willwerathia is unusually large and so far the largest known synziphosurine, with largest carapace measured about 90mm in width.[1] Prosoma of Willwerathia covered by a vaulted carapace with pointed genal spines, recurved (M-shaped) ophthalmic ridges and pairs of dorsal nodes.[1] Tergites of the opisthosoma are either incomplete or disarticulated in available fossil materials, making it difficult to reveal the original number of opisthosomal segments.[1] The opisthosoma of Willwerathia most likely compose of 10 segments, each expressed by a tergite that bore a median dorsal spine and a pair of tergopleurae (lateral extensions).[1] The opisthosoma subdivided into a wider, most likely 7-segmented preabdomen and a narrower, 3-segmented postabdomen.[1] tergite of the first opisthosomal segment is reduced in length while the remaining segments possess well-developed tergites with lateral nodes and posteriorly curved tergopleurae. The final segment terminated with a short, teardrop-shaped telson.[1]

Willwerathia was most likely a bottom-dwelling predator.[1] The marked articulation surfaces on each of the preabdominal segments suggest that Willwerathia capable to enroll itself in a way similar to Legrandella.[1] The environment in which Wilwerathia lived in was likely an estuarine to deltaic one, and other animals like the largest eurypterid, Jaekelopterus, are known from the same formation.[6]

Falcatamacaris

Willwerathia was originally thought to be an eurypterid (sea scorpion), with additional fossils described in 1998 reveal its synziphosurine affinities.[1] In the redescription done by Anderson et al. 1998, Willwerathia had been grouped under the synziphosurine family Weinberginidae alongside Weinbergina and Legrandella,[1] a classification which is not supported by phylogenetic analysis.[2] Willwerathia was regarded as part of the monophyletic Xiphosura sensu stricto (true horseshoe crab) by Lamsdell 2013,[2][7] but further phylogenetic analysis repeatedly resolving it within a clade compose of Bunodids, Pseudoniscids and Dekatriatan (chasmataspidids, eurypterids and arachnids).[8][9][10][11] Morphology of Silurian-Devonian arthropd Maldybulakia is sometimes compared to that of Willwerathia.[4][12] However, in 2020, Lamsdell found that Willwerathia bears a strong resemblance to the Cambrian artiopod Falcatamacaris, while it does not bear resemblance to other chelicerates.[3]