The Class Pycnogonida, commonly known as sea spiders, is a group of marine arthropods found in oceans worldwide, from shallow waters to deep seas. They have long, thin legs, a small body, and a proboscis used for sucking nutrients from soft-bodied invertebrates like cnidarians and sponges. Pycnogonids lack a true respiratory and excretory system, relying on diffusion for gas exchange. Most species are slow-moving and reproduce through external fertilization, with males often carrying eggs on specialized appendages called ovigers.