| Misszhouia longicaudata(Zhang&Hou,1985)and Naraoia spinosa Zhang&Hou,1985,which belong to Family Naraoiidae,are fossil arthropods that abounded in Chengjiang biota(Cambrian Series 2,Stage 3).Their bipartite but unsegmented dorsal exoskeleton consists of a head shield and a trunk shield that cover a number of biramous trunk appendages.The naraoiids are widely distributed in the Cambrian shale-type Lagerstatten,including the early Cambrian Chengjiang biota,the Sirius Passet Fauna,the Burgess Shale biota and the middle Cambrian Kaili.In geological timescale,they appeared in Cambrian and became extinct in Silurian,spanning three geological periods.Such wide spatial and temporal distributions offer good opportunities for studying their evolution.Naraoiids are abundant in Chengjiang biota,where they are frequently preserved with delicate soft parts,providing ideal material for anatomic and ontogenetic studies.In this thesis,well-preserved naraoiid individuals,including 107 M.longicaudata and 220 N.spinosa are selected from thousands of housed specimens and are investigated for appendicular structures and ontogenetic growth with the aids of micro-CT and light microscopic techniques.Based on detailed analyses on the first-handed data,a number of new findings are made:1.Brush-shape endites are distributed on the trunk appendages of M.longicaudata,which is towards the central axis of the body,with 7 spiny bumps;2.Spinose endites are distributed on the trunk appendages of N.spinosa,which is towards the central axis of the body,with 1 spiny structures;3.During the ontogenetic development of T longicaudata.the length and width of head shield and tail shield are allometric growth;the ratio of head shield to tail shield is basically unchanged,and the two are isometric growth;4.During the ontogenetic development of N.spinosa,the length and width of head shield and tail shield are allometric growth;the ratio of head shield to tail shield is basically unchanged,and the two are isometric growth. |
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