Sea spider

A marine arthropod in the class Pycnogonida, typically with a small body and long legs. Sea spiders live in oceans worldwide and are distinct from true spiders.

Pycnogonida: A class of marine arthropods commonly known as sea spiders. This is the taxonomic class that contains every sea spider.
Pycnogonid limb anatomy: The specialized arrangement of legs and appendages in sea spiders. Legs house parts of the digestive and reproductive systems, leaving little space in the small trunk.
Polar gigantism: The tendency for some polar marine animals to attain larger body sizes than related animals in warmer waters. Giant sea spiders are a prominent example of this pattern in Antarctic waters.
Araneae: The order of arachnids that includes true spiders. Despite their name, sea spiders are not members of this spider order.
Arthropod: An invertebrate animal with a segmented body, jointed appendages, and an external skeleton. Sea spiders belong to this broader animal phylum.
Sea spider respiration: Gas exchange in sea spiders, which occurs largely across the body surface and legs. Their thin, leg-dominated bodies allow oxygen to diffuse across extensive surfaces.
Evolutionary developmental biology: The study of how changes in development contribute to evolutionary differences among organisms. Sea spider body plans help investigate how arthropod limbs and segments evolved.
Chelicerata: An arthropod group that includes arachnids, horseshoe crabs, and sea spiders in many classifications. Sea spiders are often placed among chelicerates, though their precise evolutionary position remains debated.
Proboscis: An elongated feeding structure projecting from an animal's head or front body region. Sea spiders use this tube-like structure to take in food.
Open circulatory system: A circulatory system in which fluid moves through body spaces rather than remaining entirely within vessels. Sea spiders use a heart and body movements to circulate hemolymph through their bodies and legs.

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