| Skeletal Microstructures of the Chiton Ischnochiton hakodadensis and a Comparison with the Cambrian Halkieria |
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| 作者姓名： | ZHANG Xiaochuan and YAO Jinxian |
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| 作者单位： | School of Life Sciences, Peking University, Beijing 100871, China |
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| 基金项目： | Support from the National Natural Science Foundation of China (grant no. 40602001) is gratefully acknowledged. |
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| 摘 要： | Halkieria is an Early Cambrian fossil genus with proposed phylogenetic affinities ranging from stem group lophotrochozoan to stem-group aculiferan. Skeletal similarities are often cited as evidence in support of a mollusk interpretation for Halkieria and related Cambrian fossils. The skeletal microstructures of the polyplacophoran mollusk （chiton） Ischnochiton hakodadensis, which bears perinotum elements resembling sclerites of halkieriids and other coeloscleritophoran small shelly fossils （SSFs）, were studied to evaluate the interpretations. There are both similarities and differences between chiton skeletal structures and halkieriid sclerites： 1） the head valve of L hakodadensis and the dorsal shell of Halkieria evangelista share a similar pattern of fine concentric growth lines, but halkieriid dorsal shells lack other polyplacophoran valve characteristics, including V-shaped indentation, radiate ribs; 2） the arrangement of I. hakodadensis perinotum elements in three zones is somewhat similar to the arrangement pattern of halkieriid sclerites; 3） the inner perinotum scales of L hakodadensis （-200 μm in diameter） have a base and a blade, remarkably similar in morphology to halkieriid palmate sclerites （-400 μm in diameter）. However, I. hakodadensis perinotum scales are nearly solid whereas halkieriid sclerites are hollow. These observations add a microstructural dimension to the skeletal comparison between mollusks and halkeriids, and may prove to be useful in resolving the phylogenetic affinity of Halkieria and the Halwaxiidae.
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| 关 键 词： | 骨骼结构 寒武纪 微结构 软体动物 小壳化石 相似性 早寒武世 系统发育 |
| 收稿时间： | 2013/12/10 0:00:00 |
| 修稿时间： | 2014/3/25 0:00:00 |
Skeletal Microstructures of the Chiton Ischnochiton hakodadensis and a Comparison with the Cambrian Halkieria |
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| Authors: | ZHANG Xiaochuan YAO Jinxian |
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| Institution: | School of Life Sciences, Peking University, Beijing 100871, China |
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| Abstract: | Halkieria is an Early Cambrian fossil genus with proposed phylogenetic affinities ranging from stem group lophotrochozoan to stem‐group aculiferan. Skeletal similarities are often cited as evidence in support of a mollusk interpretation for Halkieria and related Cambrian fossils. The skeletal microstructures of the polyplacophoran mollusk (chiton) Ischnochiton hakodadensis, which bears perinotum elements resembling sclerites of halkieriids and other coeloscleritophoran small shelly fossils (SSFs), were studied to evaluate the interpretations. There are both similarities and differences between chiton skeletal structures and halkieriid sclerites: 1) the head valve of I. hakodadensis and the dorsal shell of Halkieria evangelista share a similar pattern of fine concentric growth lines, but halkieriid dorsal shells lack other polyplacophoran valve characteristics, including V‐shaped indentation, radiate ribs; 2) the arrangement of I. hakodadensis perinotum elements in three zones is somewhat similar to the arrangement pattern of halkieriid sclerites; 3) the inner perinotum scales of I. hakodadensis (～200 μm in diameter) have a base and a blade, remarkably similar in morphology to halkieriid palmate sclerites (～400 μm in diameter). However, I. hakodadensis perinotum scales are nearly solid whereas halkieriid sclerites are hollow. These observations add a microstructural dimension to the skeletal comparison between mollusks and halkeriids, and may prove to be useful in resolving the phylogenetic affinity of Halkieria and the Halwaxiidae. |
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| Keywords: | comparative anatomy SSFs Mollusca polyplacophoran sclerite microstructure Halkieria |
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