| Naraoiidae Temporal range: Cambrian–Silurian |
|
|---|---|
| Naraoia spinosa | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Trilobita† |
| Order: | Nectaspida |
| Family: | Naraoiidae Walcott, 1912 |
| Genera | |
The Naraoiidae is a family of soft-shelled trilobite-like arthropods that are known only from the early and middle Cambrian -- primarily from the Burgess Shale of British Columbia and the Maotianshan Shale of China.
The taxonomic placement of the Naraoiidae is uncertain; Naraoiids are similar to trilobites in many ways but have several peculiar features unlike those of other trilobite groups, primarily their unmineralized exoskeleton and unsegmented shields. Some specialists consider the Naraoiidae true trilobites of the order Nectaspida, others consider them trilobites of uncertain ordinal status, and still others consider them a separate group of non-trilobite arthropods.
There are several known genera, of which Naraoia was the first to be described and is the most widely known. The species Naraoia naraoia has an entirely unmineralized body covering and unsegmented head and body shields. Its maximum size is about 4 cm. A second softbodied trilobite - Tegopelte - is known from the same formations and is sometimes placed in the Naraoiidae, or is sometimes in its own family, the Tegopeltidae.