Ramskoeldia

''Ramskoeldia'' is a genus of amplectobeluid radiodont described in 2018. It was the second genus of radiodont found to possess gnathobase-like structures (abbreviated as GLS) and an atypical oral cone after '' Amplectobelua''. It was discovered in the Chengjiang biota of China, the home of numerous radiodontids such as '' Amplectobelua'' and ''Lyrarapax''.

Morphology

''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. 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. 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''. 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.

Taxonomy

Two species of ''Ramskoeldia'' have been described: ''Ramskoeldia platyacantha'' and ''Ramskoeldia consimilis''. 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 ''Anomalocaris saron'' owing to their similar overall appearance.

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. ''Ramskoeldia'' classified under Amplectobeluidae based on the diagnosis by Cong et al. 2018, while further phylogenetic analysis either suggest it to be a member of Amplectobeluidae (alongside ''Amplectobelua'', ''Lyrarapax'', and ''Laminacaris'') or a relatively basal radiodont.

References

Anomalocaridids

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