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2 Acta Palaeontologica Polonica

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The Burges Shale animal Oesia is not a chaetognath: A reply to Szaniawski [2005]

100%

Morris S. C.

nr 1

175-179

The Middle Cambrian Oesia disjuncta, a monospecific genus, is known only from the celebrated Burgess Shale of British Columbia. It has been re−interpreted by Szaniawski (Acta Palaeontologica Polonica 50:1–8; 2005) as a chaetognath, a distinctive phylum whose exact position in the protostomes is still controversial. Unequivocal chaetognaths, that have no similarity to Oesia, are already known to occur in the Chengjiang Lagerstätte (Lower Cambrian, S.W. China), and here I describe the first example of a chaetognath from the Burgess Shale itself. Comparisons between Oesia and chaetognaths fail to find any significant homologies. Whilst the phyletic position of Oesia is very uncertain, a place in the hemichordates may be worth exploring.

The earliest annelids: Lower Cambrian polychaetes from the Sirius Passet Lagerstatte, Peary Land, North Greenland

63%

Morris S. C. , Peel J. S.

nr 1

Apart from the Phyllopod Bed of the Burgess Shale (Middle Cambrian) polychaete annelids are practically unknown from any of the Cambrian Lagerstätten. This is surprising both because their diversity in the Burgess Shale is considerable, while to date the Chengjiang Lagerstätte which is equally impressive in terms of faunal diversity has no reliable records of any annelids. Here we describe, on the basis of about 40 specimens, Phragmochaeta canicularis gen. et sp. nov. from the Lower Cambrian Sirius Passet Lagerstätte of Peary Land, North Greenland. This makes it by far the oldest known polychaete, with a likely age of lower to middle Atdabanian, The body consists of approximately 20 segments, each bearing notochaetae and neurochaetae. The former appeared to have formed a felt−like covering on the dorsum, whilst the neurochaetae projected obliquely to the longitudinal axis. Apart from minor differences in chaetal size at either end there is no other tagmosis. Details of the head are obscure, and presence of palps, tentacles and eyes are conjectural. Jaws appear to have been absent. The gut was straight, and flanked by massive longitudinal musculature. P. canicularis was evidently benthic, propelling itself on the neurochaetae, with the dorsal neurochaetae conferring protection. Its stratigraphic position and generalized appearance are consistent with P. canicularis being primitive, but the phylogenetic relationships within the polychaetes remain problematic, principally because of paucity of relevant morphological information.