The Mobergellidae are a family of

small shelly fossils The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Camb ...

from the lower Cambrian. The small shells vary widely in shape, but are all

bilaterally symmetrical Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a pla ...

discs with paired muscle scars radiating from the centre of the internal surface.

References

Cambrian invertebrates Prehistoric animal families Cambrian first appearances Cambrian extinctions Animal families {{cambrian-animal-stub