Shucaris (pronounced as /ʃuˈkaː.ris/) (meaning "Shu's shrimp") is a genus of radiodont of uncertain taxonomic placement from the Lower Cambrian Maotianshan Shales in Yunnan, South China. The type and only species is S. ankylosskelos, known from multiple specimens comprising frontal appendages, multiple endites, gnathobase‐like structures, a nearly complete body, a head carapace complex, and one body flap associated with setal blades.[1]
Shucaris is known from multiple specimens which were all referred to S. ankylosskelos by Wu et al. (2024). The holotype, JS-0972B, consists of an isolated frontal appendage. The paratypes, JS-1950 and JS-0658, comprise a nearly complete body specimen and one partial disarticulated gnathobase-like structure, and a head carapace complex and one body flap associated with setal blades, respectively.
Shucaris appendages consist of 2 shaft podomeres and 15 distal articulated region podomeres, they're usually found curved. Podomere height decreases distally, with endites roughly the same size as them. Its endites show pairing and curve posteriorly inward on DAR 2-6 podomeres; they also bear four auxiliary spines (3 on the inner endite margin and one small spine on the outer endite margin) that increase in size ventrally, with the two spines positioned the highest potentially paired; this pairing is observable in the 5th and 6th DAR podomere. The auxiliary spines seem not to be present after the 9th DAR podomere. The 1st DAR podomere shows characteristics that are unusual for radiodonts. It bears two pairs of endites lying on the same lateral axis, with one pair in between the other. The outer pair curves distally, while the inner pair is mostly straight and points posteriorly. Both pairs bear a single auxiliary spine on each endite on their distal margin. DAR podomeres 12–15 have dorsal spines, with the largest one on the 14th podomere. The 14th DAR podomere also bears a secondary dorsal spine pair. The terminal spine is paired, which isn't observed in any other known radiodonts.
The generic name is Shucaris (pronounced as /ʃuˈkaː.ris/). 'Shu' honours Professor Degan Shu, the pioneer in the research on the Chengjiang biota and the academic leader of the Early Life Research Team at Northwest University. 'Caris', translating to ‘shrimp’ from Latin, is a commonly used suffix for marine euarthropods. The specific name, ankylosskelos (pronounced as /aŋkylosːtɛgɔs/), derives from the Greek words for 'curved' and 'leg' respectively, alluding to the curved frontal appendage.
In previous studies, Shucaris was referred to as "Radiodont C" and has been recovered as an amplectobeluid[2] and a basal anomalocaridid.[3] The results of some of these papers' phylogenetic studies have been reproduced below:
Wu et al. (2024) recovered Shucaris as a radiodont of uncertain relation—often as a member of the Anomalocarididae—in their phylogenetic analyses. Their results are shown below:
Despite this however, Wu et al., (2024) discuss novel features Shucaris possesses such as "more podomeres in the claw region than all amplectobeluids and most anomalocaridids", leading them to recover Shucaris as "the most basal taxon within Anomalocarididae or a sister taxon to the clade comprising amplectobeluids and anomalocaridids".
Shucaris had an abnormally small oral cone, suggesting that it likely chewed up prey with its gnathobase-like structures and then swallowed it. This implies that it had a similar diet to amplectobeluids, with both being nektobenthic predators consuming hard-shelled prey.