January 18, 2022

Eurypterid (sea scorpion), also known as broad-winged (Eurypterid), is an arthropod of the chelicerata classified in the extinct Eurypterid (scientific name: Eurypterida). It is a generic name. Common names such as Japanese and English have the name scorpion, but it is not a scorpion. The oldest known fossil record dates back to the Middle Ordovician Daliwiru period (about 467.3 million years ago) and prospered from the Silurian to the Devonian, and is considered to be an apex predator in the sea, especially in the Silurian. There were also types. Although it had a long habitat of about 200 million years, the last known fossil record was the Permian Changhsingian period (approximately 254-252 million years ago), the Permian period that ended the Paleozoic era. It disappeared from the geological era after the last great extinction (PT boundary). Approximately 250 species are known, and it is the most species-rich taxon among fossil chelicerata. There are many large species around 1 meter, and the largest one is estimated to reach 2.5 meters, which is known to be the largest arthropod in history. Eurypterus and Pterygotus are relatively well-known species that are commonly known as Eurypterids.


The scientific name "Eurypterida" is a general term for the scientific name "Eurypterus" (ancient Greek word "ευρυς" (eurys, broad) and "πτερον" (pteron, wing)), which is a genus of this group. One of the endings used in the scientific name of the classification group of "-ida" is added. Synonyms (nicknames) include "Eurypterid Gigantostraca" and "Cyrtoctenida". In addition to the popular name "sea scorpion" in English, there is an academic generic name "eurypterid" named after the scientific name "Eurypterida". In Chinese, it is called "Eurypterid" (simplified Chinese character: Eurypterid) by adding the character "Eurypterid" (horseshoe crab) to the translated word. In addition, there are also names such as "Eurypterid" (simplified Chinese character: Eurypterid) and "Eurypterid". The Japanese names are "Eurypterid" and "Eurypterid", which correspond to the English words "sea scorpion" and "eurypterid", respectively.


. The body is vertically long and is divided into a front body and a rear body. It is usually flat on the back of the abdomen, except for the Hibbertopteridae, which has a thick body. Most species are large arthropods, often ranging from tens of centimeters to around 1 m. It includes some of the largest known arthropods that reach over 2 m, but there are also some small species that reach only a few centimeters.


The anterior body (prosoma, or cephalothorax) is considered to be a tagma formed by the fusion of the anterior segment and the 6 segment (1-6 segment) immediately after. It is covered with a carapace or prosomal dorsal shield, and has a pair of lateral eyes, which are compound eyes, and a median eye, which is monocular in the center, on the left and right sides of the back. The carapace is wide, but not as extreme as the xiphosura, and does not cover all of the underlying appendages. The ventral surface of the carapace has an exoskeleton (doublure or ventral plate) that is placed close to the edge, and is subdivided from 1 to 5 depending on the taxon. The central part of the front end is also called "epistoma". The boundary between the exoskeleton and the carapace is also the part corresponding to the moulting crevice. Like the Xiphosura, there is an inconspicuous exoskeleton called "endostoma" in the center of the ventral surface surrounded by appendages, which is derived from the abdominal plate of the anterior body or a part released from the proximal phalanx of the fifth leg. It is considered to be a structure that does.

Chelicerae and legs

. . . . Like other cheliceraes, the ventral surface of the anterior body is a pair of cheliceraes and 5

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