Phacopina

Species belonging to the Phacopina lived from the Lower Ordovician (Tremadocian) through the end of the Upper Devonian (Famennian).

[2] The one unique feature that distinguishes Phacopina from all other trilobites are the very large, separately set lenses without a common cornea of the compound eye.

[2] The Early Ordovician genus Gyrometopus (superfamily Dalmanitoidea, family Diaphanometopidae) is probably close to the common ancestor of the Phacopina.

The natural fracture lines (sutures) of the head run along the top edges of the compound eye.

The part of the skeleton that is ‘tucked under’ (the doublure) has no sutures crossing it to form a rostral plate.The thorax has 11 (rarely 10) segments, the side lobes (or pleurae) are furrowed, and the articulating facets distinct.

Zeliszkella torrubiae , a dalmanitid, exhibiting 10 thorax segments
A schizochroal eye of Phacops rana , showing the large (0.5mm) individually set calcite lenses, that are unique in the animal kingdom
Ductina vietnamica , a phacopid that lacks eyes
Phacops rana crassituberculata , example of the Phacopoidea superfamily. Note the almost complete merger of the glabella, and the effaced pygidium
Odontochile sp. , example of the Dalmanitoidea superfamily. Note the distinct terminal spine, axis and furrows in the pygidium.
A roled-up Acastoides zguilmensis , example of the Acastoidea superfamily. Note the 3 pairs of glabellar lateral lobes.