In situ chains of Margachitina margaritana (Eisenack, 1938): a third chitinozoan egg-laying strategy

There are two competing scenarios of chitinozoan affinity: metazoan eggs versus protists. Natural aggregates (clusters and chains) of chitinozoans provide evidence that can distinguish between these possibilities. In this paper, a natural assemblage of the chitinozoan Margachitina margaritana (Eisenack, 1938) from Wenlock (Silurian) rocks of the Welsh Basin, UK is described. The chitinozoan vesicles are arranged in an array of short curved chains. Based on the morphological arrangement and sedimentology, these chains are interpreted as having originated from oviposition and thus as consisting of metazoan eggs; the assemblage indicates a strategy of laying multiple short egg-chains within a small area. This arrangement is perfectly consistent with the polycluster hypothesis, as the morphology of M. margaritana excludes formation of polyclusters. The impossibility of interpreting the assemblage as a protist-produced structure further supports a metazoan origin for chitinozoans.