Quick facts
| Known species | Wiwaxia corrugata |
|---|---|
| Group | Lophotrochozoa; exact position disputed |
| Age | Early and middle Cambrian |
| Length | A few millimetres to about 5 cm |
| Covering | Nine transverse rows of sclerites |
| Underside | Soft creeping foot |
| Feeding | Gathering and scraping food from the bottom |
| Evidence | Sclerites, gut, underside and mouthparts |
What can the fossils tell us?
Median scales were shorter, lateral scales longer and adult animals often added tall spines.
Individual sclerites were added or replaced rather than shed as one complete suit.
Function is clearer than a precise menu because diagnostic gut contents are absent.
Molluscan and annelid comparisons each explain only part of the anatomy.
Wiwaxia was a small soft-bodied Cambrian animal whose back carried rows of tough organic sclerites. Large individuals bore long spines above them. Its preserved armour, creeping underside, gut and feeding apparatus make it central to discussions of early molluscan evolution.
Sclerites and growth
The sclerites overlapped like tiles and changed shape according to position. Median elements were shorter and more rounded, while lateral elements were longer and curved. Adults often developed two rows of tall dorsal spines. These could have made attacks from above more difficult, although direct bite damage linking them to one predator is scarce.
Study of hundreds of Burgess Shale specimens revealed a gradual change in the covering. Wiwaxia did not discard its entire armour as one piece. Individual sclerites were added and replaced during growth. Juveniles differed in proportions and did not always carry the mature complement of spines.
Movement and feeding
The lower surface remained unarmoured and formed a broad foot. The animal probably crept slowly over the seafloor. A gut ran along the body, and a feeding organ at its front carried two or three rows of curved carbonaceous teeth.
Those teeth sat on a tongue-like support and could scrape microbial mats or other soft organic material. This is a close functional reconstruction, but the gut does not preserve a precise menu. The important evidence is a repeated tooth-bearing apparatus, not a particular food item placed into an illustration.
Mollusc or worm?
The sclerites have been compared with annelid bristles, whereas the foot and toothed apparatus resemble a molluscan foot and radula. Sclerite microstructure alone cannot settle the dispute because several lophotrochozoan lineages secreted comparable organic elements.
Modern analyses often place Wiwaxia near the molluscan stem group or more deeply among lophotrochozoans. Neither hypothesis makes it a modern slug in armour. Its character combination belonged to an early extinct branch.
Unlike the panarthropod Hallucigenia and predatory Anomalocaris, it represents a different major line of animal evolution. The catalogue keeps those relationships separate instead of grouping them by unusual appearance alone.
Evidence, inference and reconstruction
| Direct | Rows of sclerites, long spines, underside, gut and toothed apparatus |
| Inference | Slow crawling and scraping of soft food from the substrate |
| Uncertain | Exact lophotrochozoan position and detailed diet |
| Reconstruction | Colour, muscle movement and the food shown in a scene |
Frequently asked questions
Was Wiwaxia a mollusc?
It may lie near the molluscan stem group, but its exact position among lophotrochozoans remains disputed.
What were the long spines for?
Defence is the most likely role, although no single predator or attack method is directly demonstrated.
How did Wiwaxia move?
It probably crept slowly over the bottom on a broad, soft and unarmoured foot.
What did Wiwaxia eat?
Its toothed apparatus could scrape soft organic food and microbial coatings from the seafloor.