Sea Spider Sea spiders are a species of arthropods that can have four, five or six pairs of walking legs and live in ocean waters. They have a body that is difficult to determine because their legs dominate. Most sea spiders are very small with lengths from one to 10 millimeters. Some may reach one foot in length and are found in deep polar sea regions. Because of their small size, their tiny muscles consists of one single cell that is surrounded by connective tissue which connects the muscles to its exoskeleton for movement. The front segment of the sea spider called the anterior region allows for very little lateral movement. A sea spider's legs are segmented into nine sections. Those that live near the seashore have short, thick legs and move slowly. Those that live in deeper waters have longer, thinner legs and are move quickly on the lips of their legs. Most sea spiders are also able to swim.