Figure 1

Examples of eurypterid and limulid morphology and comparison of Jaekelopterus lateral eyes to other arthropod compound eyes. (a) Reconstruction of Jaekelopterus rhenaniae (Jaekel, 1914) (modified from Braddy et al. 2008; drawing by S. Powell, with permission. (b) Tachypleus gigas (Müller, 1785), Limulida [© Subham Chatterjee/CC BY-SA 3.0 (via Wikimedia Commons)]. (c–e) Examples of specimens (c: GIK 186, d: GIK 188, e: GIK 190). (f–h) Compound eye of a hornet Vespa crabro germana Christ, 1791. (i–k) Compound eye of Carcinoscorpius rotundicauda (Latreille, 1802), Limulida, exuviae. (l) Compound eye of the trilobite Pricyclopyge binodosa (Salter, 1859), Ordovician, Šárka formation, Czech Republic. (m) Ommatidium of the trilobite Schmidtiellus reetae Bergström 1973, base of the Lower Cambrian, Lükati Fm., Estonia. (n–p) Cones (lens cylinders) of the internal side of the compound eye of C. rotundicauda (exuvia). (q) Impressions of the exocones in Jaekelopterus rhenaniae (Jaekel, 1914), (GIK 186a). (r–t) Exocones of J. rhenaniae (GIK 186), note the regular arrangement compared to (i). (u) Schematic drawing of the ommatidium of an aquatic mandibulate (crustacean), and of the ommatidium of a limulid. (w) schematic drawing of several ommatidia of a limulide. (x) Schematic drawing of crossections of (v), the limulide after⁷³. (y) Visual unit of a limulide (redrawn and changed after⁵¹). cc, crystalline cone; ec, eccentric cell; exc exocone; l, lens; p, pigment; pc, pigment cells; rc, receptor cells; rh, rhabdom; su sensory unit.