Panopod horseshoe crab pinyin: [bǎn zú hòu]

Panopod horseshoe crabs are a group of extinct arthropods that lived about 420 million years ago. They were similar to paddle-footed horseshoe crabs, with a cephalic, thoracic, and abdominal body divided into the head, which consisted of six segments, and the ventral surface of the body, which had six pairs of appendages, the last pair of which were plate-like and used for swimming.

Paddle-footed horseshoe crabs are an important class of arthropods that survived in the Paleozoic Era, and are close relatives of the modern arachnid family, commonly known as sea scorpions because of their scorpion-like shape. The horseshoe crabs first appeared in the Ordovician period, reached the peak of diversity in the Silurian period, and then declined and became extinct at the end of the Permian period.

The horseshoe crab, which has attracted much attention for its unique appearance, was the "star animal" of the Silurian period (about 430 million years ago).

The horseshoe crab has a high degree of ecological diversity, occupying positions in a variety of ecological environments, including marine, freshwater, and terrestrial environments, and is an important medium for understanding ecological changes during the Paleozoic Era.

Mixed-winged horseshoe crabs are a family-level taxonomic unit under the suborder of Plate-footed Horseshoe Crabs, and the third pair of appendages of this group is highly specialized, with long spines and exaggerated morphology. The unique and highly recognizable appendages of the horseshoe crab are similar to the whisker limbs of extant whip spiders, and are thought to be used for immobilizing prey, a sign of the horseshoe crab's greater predatory ability.

Panopod horseshoe crabs have a small cephalothorax, a segmented abdomen, the first seven segments make up the anterior abdomen with appendages, and the last five segments make up the posterior abdomen without appendages, with a tail sword, and the last pair of stepping feet are in the shape of a plate, so it is called a panopod horseshoe crab, which is used for swimming. There are 6 pairs of book gills on the abdomen.

The first pair of front legs of the horseshoe crab are called chelicerae, which are similar to the canine teeth of spiders, and the other four pairs of appendages are steppers, and the limbs are cylindrical and spiny, which extend backward along the body, and the limbs increase in size, and the sixth pair of limbs are a pair of very large and smooth flat paddles, which are located on the thorax and are retracted to allow for swimming.

They have no antennae, and the mouthparts are bordered by a small, U-shaped endostomal plate, which is covered by a larger postoral plate that is part of the abdomen.