Ramskoeldia

Ramskoeldia is known only from a few frontal appendages, gnathobase-like structures (GLSs), disarticulated smooth and tuberculated plates interpreted as parts of their oral cones, as well as fragments of body flaps and head carapace complex.^[1] The frontal appendage of Ramskoeldia is composed of 16 podomeres (3 shaft podomeres and 13 distal articulated region podomeres), with endites of podomeres 4 to at least podomere 12 bearing prominent auxiliary spines.^[1] The endites of podomere 4 (first podomere of distal articulated region) is the largest compared to other endites, but not extremely enlarged like those of Amplectobelua.^[1] The size of the endites alternates (those on even podomeres being larger than that of the odd podomere following it) and decreasing distally, except podomere 8 is larger than podomere 6 just like Amplectobelua. Compared to Amplectobelua, the GLSs of Ramskoeldia are wider and the three pairs of GLSs did not gradually alternate in size.^[1]

Two species of Ramskoeldia have been described, R. platyacantha and R.? consimilis, but the taxonomic placement of latter species within this genus has been consistently questioned by subsequent studies.^[2][3][4] The endites of R. platyacantha are stout and their length does not exceed the height of the podomere to which they attach. The shaft podomeres 2 and 3 of R. platyacantha also bore prominent endites resembling those of distal articulated podomeres. Conversely, in R. consimilis, the endites of the distal articulated region are slender and most of them have a length that exceeds the height of podomere to which they attach. The shaft of R. consimilis has only a simple endite on podomere 3. The frontal appendages of R. consimilis had been previously misidentified as Houcaris saron owing to their similar overall appearance.^[1]

Due to the numerous shared characters with Amplectobelua (e.g. larger endites of podomere 8; irregular oral cone; presence of GLSs), the discovery of Ramskoeldia questioned the amplectobeluid affinity of Lyrarapax, a presumed amplectobeliud genus which lacking characters noted above.^[1] Ramskoeldia classified under Amplectobeluidae based on the diagnosis by Cong et al. 2018,^[1] while further phylogenetic analysis either suggest it to be a member of Amplectobeluidae (alongside Amplectobelua, Lyrarapax, and Laminacaris)^[5] or a relatively basal radiodont.^[6]