The Pycnogonida are a group of marine arthropods known as "sea spiders" for their resemblance to true, terrestrial spiders. Although there has been much debate during the past century regarding which arthropod groups are their closest relatives, growing consensus places the pycnogonids as an early branching lineage that is the sister group to the chelicerates (arachnids plus horseshoe crabs) (Giribet and Edgecombe 2012).
There are around a thousand described species of pycnogonids (and probably hundreds more not yet described). They are found worldwide from the intertidal zone to depths of nearly 7,000 m. Most pycnogonids are small, with leg spans of less than a centimeter (in some species, just a few millimeters), but some deep-sea species have leg spans of up to 60 cm. Many species are errant (i.e., they actively move about), but others live on seaweeds or on other invertebrates, such as sea anemones, hydroids, ectoprocts, and tunicates (at least one or two species live on the bells of pelagic medusae and pycnogonids have also been observed on the huge vestimentiferan worms living in the hydothermal vent community of the Galapagos Rift).
The walking legs of pycnogonids are 9-segmented. Most of the commonly encountered intertidal species have short, thick legs and are quite sedentary, moving very slowly. Deep-water bottom-dwelling species tend to have longer, thinner legs and to be more active, walking on the tips of their legs. Many pycnogonids are also known to swim periodically.
Most species are generalist predators (and, in many cases, scavengers), although a few feed on algae. Food is obtained by sucking it through the proboscis (often just body fluids and tissue fragments from their prey.).
Pycnogonids are dioecious (i.e., with separate males and females) and embryos are brooded by the male. In many species, distinctive 6-legged larvae (immature forms) are released by the brooding male that live in some sort of symbiotic relationship with cnidarians, molluscs, or echinoderms.
(Brusca and Brusca 2003)
Bamber and El Nagar provide an online database on pycnogonid names, taxonomy, museum specimens, and literature.
The Pycnogonida, also known as the Sea Spider, is a class of unidentified aquatic Chelicerata’s in the Pantopoda order and has many genera including the Pseudopallene circularis.
The Sea Spiders are mainly found in the Mediterranean Sea but can be seen in the Atlantic Ocean, Artic Ocean, and Caribbean Sea. They have a similar look to a common spider but can be larger; their size varies on their environment and has longer legs than most Arachnids. These aquatic animals are best known for its long legs and similar look to Arachnids though they are in the Chelicerata subphylum.
An adult male can be as large as 76 centimeters (Around 2.8 feet) in length from leg to leg and as small as 5 centimeters. It is a very light weight class as heavy as .7kg (1 pound) and as light as .01kg (.1 pounds). Sea Spiders have a proboscis out of its mouth that sucks out the nutrients of prey.They have a small center and 8 legs but can have 10 or 12 legs. They craw or swim with its legs pushing down the water. The color greatly varies from yellow to even blue.
They have no found origins yet because only two complete fossils have been found. It seems they are most often found in the Atlantic Ocean near Europe and in the Mediterranean Sea. The fossils were found in these areas. These animals have many connections and seem to have originated from crabs and a form of early spider. They have only one common ancestor that we know as and that is to the prehistoric monkey-spider hybrid.
The Pycnogonida are predators of many soft tissued invertebrates. They mainly feast on sponges. They keep to themselves and stay hidden most of the time. They have no one predator that lives off of them. They live in small communities and are rarely found. Their only defense is their legs with contain a poison of sorts that disables the attacker or prey.
There are no recorded discoverers of the Pycnogonida. Many biologists are trying to discover the connections of the Sea Spiders and discover more genus and species. There are many genus recorded but no intense studying of just one.
The Pycnogonida Sea Spiders are a very elusive and new class. They are magnificent in their ways or live and should have more in-depth studies in my view.
