Early Ordovician (Tremadoc) – Middle Devonian
Cheiruridae is an extinct family of fast-moving low-level epifaunal carnivores
Description of the Family
- Pleurae with pointed or bluntly rounded spines and oblique or transverse pleural furrows
- Pygidium with 2 to 4 pairs of pleural ribs and spines
- Surface commonly tuberculate, pitted, or both
- Antennae uniramous
- Gill braches bearing filaments only on distal segments
Treatise on Invertebrate Paleontology, Part O (1959):
- Pleurae with pointed or bluntly rounded spines and oblique or transverse pleural furrows, in some genera represented by row of pits, or effaced. Pygidium with 2 to 4 pairs of pleural ribs and spines; axial rings few. Surface commonly tuberculate, pitted, or both. Appendages only of Ceraurus described; antennae uniramous, other appendages biramous, with gill braches bearing filaments only on distal segments.
- The Cheiruridae proper have really more of the characters of the Phacopidae than appears at first sight, for those loosely built Trilobites have the eyes reticulate externally, though on a smaller scale than Phacops, and the facial suture ends upon the exterior, not the posterior, margin. The normal number of body-rings is eleven. With these points of resemblance, important as they are, the analogy ceases, for the short, oblique furrow and free ends of the nodular pleurae give a very marked aspect; and the tail is of few joints, and the ends of their pleurae are also free.