title: Sperm carriers in Silurian sea scorpions.
abstract: Invasion of the land by arachnids required adaptations of numerous organs, such as gills evolving into lungs, as well as mechanisms facilitating sperm transfer in a terrestrial environment. Many modern arachnids use spermatophores for this purpose, i.e. sperm transmitters detached from the body. Exceptionally preserved Silurian (423 Ma) fossils of Eurypterus tetragonophthalmus Fischer, 1839 (Chelicerata: Eurypterida) preserve so-called 'horn organs' which we here demonstrate as being equivalent to the spermatophore-producing parts of the genital tract in certain modern arachnids. This clarifies a long-running debate about sexing eurypterids based on the shape of the median abdominal (or genital) appendage. To our knowledge this is also the oldest direct evidence for spermatophore-mediated sperm transfer in the fossil record and suggests that eurypterids had evolved mating techniques using spermatophores as early as the Silurian, a valuable prerequisite for life on land. Spermatophores are absent in sea spiders (Pycnogonida) and horseshoe crabs (Xiphosura); thus the shared presence of sclerotized sperm-transfer devices in eurypterids and arachnids is a novel character, newly elucidated here, which offers explicit support for (Eurypterida + Arachnida). For this clade the name Sclerophorata n. nov. is proposed. Arachnida can be further defined by fusion of the originally paired genital opening.
authors: American Museum of Natural History, New York, USA. CarstenKamenz@gmx.de
authors: Carsten
authors: C
authors: Kamenz
authors: Andreas
authors: A
authors: Staude
authors: Jason A
authors: JA
authors: Dunlop
mesh_terms: D000818:Animals; D001097:Arachnida / Q000033:anatomy & histology* / Q000145:classification; D005580:Fossils; D008297:Male; D012098:Reproduction / Q000502:physiology; D013093:Spermatogonia