湖北莱氏虫的胸肋畸形

MALFORMED THORACIC PLEURAE OF REDLICHIA (REDLICHIA) HUPEHENSIS HSU

湖北莱氏虫[Redlichia (Redlichia) hupehensis Hsü,1948]最早发现于湖北宜昌下寒武统,当时许杰、马振图认为它是下寒武统上部的化石。1979年,笔者在江西省彭泽县龙官洞附近进行地质调查时,于龙宫洞真岩以南(龙宫洞东1km)早寒武世王音铺组的绿色页岩及钙质粉砂岩中采到一批三叶虫化石,计有Redlichia (Redlichia) hupehensis Hsü, R. (Pteroredlichia) chinensis Walcott, R. (P.) yilongensis Zhang et Lin, Arthricocephalus sp.。从化石组合来说,应归属张文堂、卢衍豪等(1980)

The fossil was Collected from the calcareous shale intercalated with silty shale in the Lower Cambrian Wangyinpu Formation located at about 1 km east of Longgongdong in Pengze County, Jiangxi. It was in association with RedIichia (Redlichia) hupehensis Hsu, R. (Pteroredlichia) chinensis Walcott, R. (P.) yilongensis Zhang et Lin and Arthricocephalus sp.The malformed specimen is identified as Redlichia (Redlichia) hupehensis Hsu, with complete cranidium, thorax, and pygidium except a pair of free cheeks, representing a moulted old exoskeleton. The 5th—7th segments on the right side of thoracic pleurae show abnormality. The fifth pleural spine is truncated, with the postero-pleural margin undulate in appearance. The 6th and 7th pleurae are fused, with the outer margih intersecting obliquely across the pleurae. The front margin of the 6th pleura shows undulate and tallies with the posterior margin of the 5th one. The fused line of 6th and 7th pleurae extendforward diagonally, and the 7th pleura in front of the pleural furrow considerably expands, forming an unnatural trilateral.From A. W. Owen's (1985) statistics, only K. Saito (1934) had reported from north-western Korea about the Redlichia segment fused with the pygidium. We consider that the damage in the distal soft parts of the specimen was caused by he withdrawal of the newborn soft dorsal exoskeleton from the narrow gap between the dorsal exoskeleton and ventral margin during the moulting process, with cicatrizations formed by later compensation growth.