| Illaenus Temporal range:
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| Illaenus tauricornis from Russia. On display at the Museo Civico di Storia Naturale di Milano | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | †Trilobita |
| Order: | †Corynexochida |
| Family: | †Illaenidae |
| Genus: | †Illaenus Dalman, 1827 |
Illaenus is a genus of trilobites from Russia and Morocco, from the middle Ordovician.
Species included in this genus can reach a length of about 57 millimetres (2.2 in). They are without glabella and without articulation of the tail. The cephalon has a high profile and recurved genal spines. Eyes are distant from the axis of the head, situated nearer to the edge.[1][2]