Ippolitov, A.P., Vinn, O., Kupriyanova, E.K. and Jäger, M. 2014. Written in stone: history of serpulid polychaetes through time. Memoirs of Museum Victoria 71: 123-159.Although the fossil record of annelids in general is poor, calcareous tube-building Serpulidae are a notable exception. The "stumbling block" of understanding the serpulid fossil record is obtaining reliable taxonomic interpretations of fossil tubes based on morphology. Luckily, serpulid tubes demonstrate high variety of ultrastructures and nonuniform mineralogical composition, which can be used as new tools for decrypting the fossil record. Ancient Late Ediacaran (580-541 Ma) and Paleozoic (541-252 Ma) rocks contain diverse tubicolous fossils that have often been erroneously interpreted as annelids, and serpulids, in particular. Palaeozoic to Middle Jurassic coiled spirorbiform tubes, often referred to as Spirorbis, had been shown to be microconchids, a group of probable lophophorate affinity. The most ancient records of unequivocal serpulids date back to the Middle Triassic (~244 Ma) of the Mesozoic, and from the Earliest Jurassic (~200 Ma) fossil serpulids become common. From the latest Jurassic (~146 Ma) serpulids colonised hydrocarbon seep environments and possibly also penetrated the deep sea. Concerted efforts of paleontologists and zoologists are needed for further understanding of serpulid evolutionary history. The serpulid fossil record can become a valuable instrument for calibration of "molecular clocks" in polychaetes, which would allow dating not only divergence events in serpulids, but also in annelid groups that lack a representative fossil record.
This is the second paper of the series started with Ippolitov and Rzhavsky (2014) providing detailed descriptions of recent spirorbin tubes, their mineralogy and ultrastructures. Here we describe species of the tribe Spirorbini Chamberlin, 1919 that includes a single genus Spirorbis Daudin, 1800. Tube ultrastructures found in the tribe are represented by two types-irregularly oriented prismatic (IOP) structure forming the thick main layer of the tube and in some species spherulitic prismatic (SPHP) structure forming an outer layer and, sometimes, inner. Mineralogically tubes are either calcitic or predominantly aragonitic. Correlations of morphological, ultrastructural, and mineralogical characters are discussed. All studied members of Spirorbini can be organized into three groups that are defined by both tube characters and biogeographical patterns and thus, likely correspond to three phylogenetic clades within Spirorbini.
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