Limulus polyphemus (Linnaeus, 1758)

Limulus polyphemus View in CoL

The extant American horseshoe crab has reniform LCEs with visible ommatidia ( Fig. 7A–E View Figure 7 ; Harzsch et al., 2006; Miether & Dunlop, 2016; Strausfeld et al., 2016). Limulus polyphemus LCEs can have> 1000 ommatidia, and Poschmann et al. (2016) suggested an average lens width of 0.14 mm. This value depends on the age, size, and sex of a given specimen. This taxon contrasts with other extant chelicerates that have more derived eyes and a greatly reduced number of lenses ( Battelle, 2006; Harzsch et al., 2007). Lateral compound eyes on the studied specimen are located in the centre of the cephalothorax, 22 mm from the lateral border on both sides of the cephalothorax and located along well-defined ophthalmic ridges ( Fig. 7D, E View Figure 7 ; Bicknell et al., 2018).