†Albalimulus Bicknell & Pates, 2019 Ballagan Formation, Scotland, Early Carboniferous (Tournaisian) (Considered Xiphosura incertae sedis by Lamsdell, 2020) †Casterolimulus Holland, Erickson & O'Brien, 1975 Late Cretaceous (Maastrichtian) Fox Hills Formation, North Dakota, USA (Inconsistently placed in this family) †Heterolimulus gadeai Vıa & Villalta, 1966 Alcover Limestone Formation, Spain, Middle Triassic (Ladinian) †Limulitella Størmer, 1952 Middle-Upper Triassic, France, Germany, Tunisia, Russia †Sloveniolimulus Bicknell et al., 2019 Strelovec Formation, Slovenia Middle Triassic (Anisian) †Tarracolimulus Romero & Vıa Boada, 1977 Alcover Limestone Formation, Spain, Middle Triassic (Ladinian) †Victalimulus Riek & Gill, 1971 Lower Cretaceous (Aptian) Korumburra Group, NSW, Australia †Yunnanolimulus Zhang et al., 2009 Middle Triassic (Anisian), Guanling Formation, Yunnan, China †Mesolimulus Middle Triassic-Late Cretaceous England, Spain, Siberia, Germany, Morocco †Ostenolimulus Lamsdell et al. 2021 Early Jurassic (Sinemurian) Moltrasio Limestone, Italy †Volanalimulus Lamsdell, 2020 Early Triassic, Madagascar. Subfamily Limulinae Leach, 1819 †Crenatolimulus Feldmann et al., 2011 Upper Jurassic (upper Tithonian) Kcynia Formation, Poland. Lower Cretaceous (Albian) Glen Rose Formation, Texas, USA Limulus O. F. Müller, 1785 Pierre Shale, United States, Late Cretaceous (Maastrichtian), Atlantic North America, Recent Subfamily Tachypleinae Pocock, 1902 Carcinoscorpius Pocock, 1902, Asia, Recent Tachypleus Leach, 1819 Upper Cretaceous (Cenomanian) Haqel and Hjoula Konservat-Lagerstatten, Lebanon, Upper Eocene Domsen Sands, Germany, Asia, Recent Cladogram after Lasmdell 2020. Anatomy The entire body of the horseshoe crab is protected by a hard carapace. It has two compound lateral eyes, each composed of about 1,000 ommatidia, plus a pair of median eyes that are able to detect both visible light and ultraviolet light, a single parietal eye, and a pair of rudimentary lateral eyes on the top. The latter become functional just before the embryo hatches. Also, a pair of ventral eyes is located near the mouth, as well as a cluster of photoreceptors on the telson. Having relatively poor eyesight, the animals have the largest rods and cones of any known animal, about 100 times the size of humans, and their eyes are a million times more sensitive to light at night than during the day. They use their chelicerae—a pair of small appendages—for moving food into the mouth. The next five pairs of appendages, the first of which are the pedipalps, are used for locomotion (ambulatory legs). The mouth is located in the center of the legs, whose bases are referred to as gnathobases, and have the same function as jaws and help grind up food. In extant species their appendages are uniramous,