query: taxon_rank rhenopterus
supports: An arthropod (from Greek "arthro-", joint + "podos", foot) is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages (paired appendages). Arthropods form the phylum Arthropoda, which includes the insects, arachnids, myriapods, and crustaceans. 
  Arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Their versatility has enabled them to become the most species-rich members of all ecological guilds in most environments. They have over a million described species, making up more than 80% of all described living animal species, some of which, unlike most animals, are very successful in dry environments. Rhenopterus is an extinct prehistoric eurypterid . Rhenopterus lived in the Lower Devonian period in Europe and possibly North America . The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods, respectively. Lapworth, recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, and placed them in a period of their own. It received international sanction in 1960, when it was adopted as an official period of the Paleozoic Era by the International Geological Congress. Scorpions are predatory arachnids of the order Scorpiones. They have eight legs and are easily recognized by the pair of grasping pedipalps and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger. Scorpions range in size from 9 mm / 0.3 in. ("Typhlochactas mitchelli") to 23 cm / 9 in. ("Heterometrus swammerdami"). Arachnids are a class (Arachnida) of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. All arachnids have eight legs, although the front pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs. The term is derived from the Greek word ("aráchn"), meaning "spider". Spiders are the largest order in the class. Eurypterids (sea scorpions) are an extinct group of arthropods related to arachnids that include the largest known arthropods to have ever lived. They are members of the extinct order Eurypterida (Chelicerata); which is the most diverse Paleozoic chelicerate order in terms of species. The name Eurypterida comes from the Greek words ' (meaning "broad" or "wide") and ' (meaning "wing"). This name was chosen due to the pair of wide swimming appendages on the first fossil eurypterids discovered. The largest, such as "Jaekelopterus", reached in length, but most species were less than . They were formidable predators that thrived in warm shallow water, in both seas and lakes, from the mid Ordovician to late Permian. Jaekelopterus ("Otto Jaekel's wing) is an extinct genus of sea scorpion. "Jaekelopterus" lived approximately 390 million years ago. At an estimated length of , it is the largest known arthropod ever discovered, surpassing the "Pterygotus" and even the millipede-like "Arthropleura". There are two species, one being the type species, "J. rhenaniae", from freshwater strata in the Rhineland, and "J. howelli" from estuarine strata in Wyoming. The subphylum Chelicerata (or ; New Latin, from French "chélicère", from Greek "khl" "claw, chela" and "kéras" "horn") constitutes one of the major subdivisions of the phylum Arthropoda. It contains the horseshoe crabs, sea spiders, and arachnids (including scorpions and spiders).
candidates: class form genus group order phylum species subphylum tribe
answer: genus