| Tetrophthalmi Temporal range:
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|---|---|
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| A reconstruction of Hastocularis argus showing dorsal, lateral, ventral, and anterolateral views | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Arachnida |
| Order: | Opiliones |
| Suborder: | †Tetrophthalmi Garwood, Sharma, Dunlop & Giribet, 2014 |
| Genera | |
| Diversity | |
| 2 species | |
Tetrophthalmi is an extinct suborder of Opiliones (commonly known as harvestmen or daddy-longlegs) that had both median and lateral eyes. First described in 2014, it is known from two extinct species. Phylogenetic analysis suggests that this eye arrangement is the ancestral condition for harvestmen, placing Tetrophthalmi and Cyphophthalmi in a basal position within Opiliones.
In 2024, a study discovered that living members of Opiliones have retained lateral eyes, as well as a second pair of vestigial median eyes. A reanalysis of harvestman phylogeny based on 78 genes and an updated understanding of morphology revealed that Tetrophthalmi are derived members of the living suborder Eupnoi (true daddy-longlegs).[1]
- ^ Gainett, Guilherme; Klementz, Benjamin C.; Blaszczyk, Pola; Setton, Emily V.W.; Murayama, Gabriel; Willemart, Rodrigo H.; Gavish-Regev, Efrat; Sharma, Prashant (February 23, 2024). "Vestigial organs alter fossil placements in an ancient group of terrestrial chelicerates". Current Biology.