The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids, as well as a number of extinct lineages, such as the eurypterids and chasmataspidids.
Sea spiders are marine arthropods of the order Pantopoda, belonging to the class Pycnogonida, hence they are also called pycnogonids. They are cosmopolitan, found in oceans around the world. The over 1,300 known species have leg spans ranging from 1 mm (0.04 in) to over 70 cm (2.3 ft). Most are toward the smaller end of this range in relatively shallow depths; however, they can grow to be quite large in Antarctic and deep waters.
Nymphonidae is a family of sea spiders which has representatives in all the oceans. This family contains some 250 species, most of which are found in the genus Nymphon. Nymphonid bodies are between 1 and 15 mm long, the extent between the points of the legs reaching 150 mm. Most species are predators of hydroids. Like most sea spiders, species in this family have four pairs of legs, except for Pentanymphon antarcticum, which has five pairs, and Sexanymphon mirabilis, which has six pairs.
The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired appendages, which in ancestral forms would have appeared more like legs than mouthparts. In general, arthropods have mouthparts for cutting, chewing, piercing, sucking, shredding, siphoning, and filtering. This article outlines the basic elements of four arthropod groups: insects, myriapods, crustaceans and chelicerates. Insects are used as the model, with the novel mouthparts of the other groups introduced in turn. Insects are not, however, the ancestral form of the other arthropods discussed here.
Mixopterus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Mixopterus have been discovered in deposits from Late Silurian age, and have been referred to several different species. Fossils have been recovered from two continents; Europe and North America.
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The larvae of crustaceans often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults, more-so than where the larvae are planktonic, and thereby easily caught.
Alitta succinea is a species of marine annelid in the family Nereididae. It has been recorded throughout the North West Atlantic, as well as in the Gulf of Maine and South Africa.
Nymphon is a genus of sea spiders in the family Nymphonidae. The species of sea spiders within the genus Nymphon are all benthic organisms and are found in abyssal and bathyal areas of the ocean. This is a fully marine group and can be found at various depths ranging from the littoral zones to the deep sea. They are found in most major oceans across the globe with a strong distribution around polar regions: Arctic and Antarctic waters. Out of the sea spider genus, Nymphon is the most rich, with a majority of the species within the genis being found in the Southern Ocean region. This genus may also contain bioluminescent species.
Pycnogonidae is a family of sea spiders.
Pycnogonum is a genus of sea spiders in the family Pycnogonidae. It is the type genus of the family.
Pycnogonum stearnsi, commonly known as Stearns' sea spider, is a marine arthropod in the family Pycnogonidae. It is found on the western seaboard of North America.
Nymphon brevirostre is a species of sea spider first described by George Hodge in 1863. The species highly resembles other members of the genus Nymphon, and species identification from morphological traits alone is therefore a complex task.
Nymphon leptocheles is a species of sea spider first described by Georg Ossian Sars in 1888. The species greatly resembles other members of the genus Nymphon, and species identification from morphological traits alone is therefore a complex task.
Nymphon signatum, the scarlet sea spider, is a species of sea spider.
Eulalia clavigera is a species of polychaete worm in the family Phyllodocidae, native to the coasts around Britain, through Western France, and to the Iberian Peninsula. It closely resembles Eulalia viridis, and there has been confusion in the past as to the identification of the two species.
Scolelepis squamata is a species of polychaete worm in the family Spionidae. It occurs on the lower shore of coasts on either side of the Atlantic Ocean.
Necrogammarus salweyi is the binomial name applied to an arthropod fossil discovered in Herefordshire, England. The fossil represents a fragmentary section of the underside and an appendage of a pterygotid eurypterid, a group of large and predatory aquatic arthropods that lived from the late Silurian to the late Devonian. The Necrogammarus fossil is Late Silurian in age and its generic name means "dead lobster", deriving from Ancient Greek νεκρός and Latin gammarus ("lobster").
Caprella penantis is a species of skeleton shrimp in the family Caprellidae. It lives on the seabed in shallow water in many parts of the world. This species was first described in 1814 by the English zoologist William Elford Leach who named it Caprella penantis in honour of the Welsh naturalist Thomas Pennant. The type locality is Devon, England.
Palaeoisopus is a monotypic genus of fossil pycnogonid, known only by one species, Palaeoisopus problematicus, discovered from the Lower Devonian Hunsrück Slate of Germany. It have several characters unusual for a pycnogonid, such as swimming legs with alternating size, medially-arranged eyes, and most significantly, a long, segmented abdomen, which were highly reduced in modern counterparts.
Pycnogonum litorale is a marine arthropod in the family Pycnogonidae, the sea spiders. It is found in the northern Atlantic Ocean, the North Sea, the English Channel and the western Mediterranean Sea.
