Giant sea spiders are not actually spiders, but are marine arthropods that belong to the Pycnogonida class. Facts about their growth, habitat and reproduction are very interesting, though, so here is some helpful information about them.
Giant sea spiders are also called pantopoda or pycnogonids. They can usually be found inside shallow waters and at a 7000 meter depth anywhere in the world, most of all in the Mediterranean and Caribbean seas and the Arctic and Antarctic oceans. Almost 1300 species of these sea spiders exist today, which can be divided into 86 genera and 8 families. Their sizes vary from several millimeters to 75 centimeters of leg span.
These giant sea spiders can swim like pulsing umbrellas and feed by sucking juice out of soft-bodied invertebrates with the help of their long proboscis. They usually feed on cnidarians, bryozoans, sponges and polychaetes.
Although they have little bodies and no respiratory system, they can have up to six pairs of long walking legs. They exchange gas through a direct diffusion process and their body only has two parts: the cephalothorax and the abdomen, which is also extremely small. The digestive system has a diverticula that extends to the legs, too.
Their bodies get support from a non-calcareous exoskeleton consisting of thick and hard ectocuticles, thin epicuticles and flexible and soft endocuticles, with which their joints can move. They have eye turrets that support four basic eyes, providing great all-round detection of light. The cuticles have pits and hairs, too, that act as tactile and chemosensory sense organs.
Pycnogonids have long, small and thing hearts that beat up to 180 times a minute to create enough blood pressure. Their circulatory system is open and they have brains in their nervous system that connect to two nerve cords which, in turn, connect to certain other nerves.
Giant sea spiders are extremely small, with each small muscle only containing one cell and connective tissues. The body’s head has two pairs of proboscis and non-walking appendages called chelifores that sometimes aren’t even there. Such species have well-developed proboscis that are more mobile and flexible. They also offer up numerous sensory bristles, as well as strong rasping mouth ridges.