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sea spider

sea spider, common name for members of the class Pycnogonida, long-legged, rather spiderlike organisms of the subphylum Chelicerata, widely distributed in marine waters. Most are tiny, from 1 to 9 mm (0.04–0.36 in.), and live in littoral regions, crawling about over the surface of sessile animal colonies or seaweeds. Some live on or in clams. There are deep-sea forms, some becoming quite large; Colossendeis colossea has a leg span of nearly 2 ft (91 cm). Their unusual body form makes their relationships to other arthropods obscure. Nearly all of the body is composed of the anterior region (prosoma); a tiny tubular posterior region (opisthosoma) projects behind. A large proboscis is used to suck in food. At the base of the proboscis is a pair of modified appendages (chelicera) used to pick off bits of food and hold them in front of the mouth. The next appendages are a pair of leglike pedipalps, followed by a pair of specialized legs used by the male to carry eggs until they hatch. Four pairs of walking legs follow, but sometimes additional pairs are found. Members of this class are relatively common and widely distributed; well over 400 species are known. Sea spiders are classified in the phylum Arthropoda, subphylum Chelicerata, class Pycnogonida.

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Pycnogonida

Pycnogonida (Pantopoda; sea spiders; phylum Arthropoda, subphylum Chelicerata) A class of marine chelicerates, all of which are small (total body length usually 1–10 mm but up to 6 cm in some species, with a leg span of 75 cm). The narrow body comprises a cephalon and four–six distinct segments, the cephalon bearing a proboscis. The posterior part of the cephalon tapers to form a neck bearing four eyes mounted on a central tubercle on its dorsal surface. There is a pair of chelifores (possibly homologous to arachnid chelicerae), a pair of palps, and two pairs of ovigers (reduced in some species and absent in females of some species). The four–six pairs of eight-segmented walking legs articulate with large processes, pairs of which project from each segment, giving the animal the spider-like appearance to which its common name refers. Some species have eight–ten pairs of legs, possibly as a result of polyploidy. Most pycnogonids are carnivorous and bottomdwellers, although some can swim. There are about 500 species found in all oceans, but more commonly in cold waters, and at all depths.

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Pycnogonida

Pycnogonida See Chelicerata.

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sea spiders

sea spiders See PYCNOGONIDA.

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Sea Spiders

Sea Spiders

Sea spiders (phylum Arthropoda, class Pycnogonida) are a group of arthropods that take their common name from their superficial resemblance to the true spiders. Although rarely seen, these are widespread animals occurring in every ocean, with a preference for cooler waters. Sea spiders occupy a wide range of habitats: some species have been recorded from a depth of 19,685 ft (6,000 m), but the majority live in shallow coastal waters. Some 1,000 species have been identified.

Most sea spiders are small animals, measuring from 0.04-0.4 in (1-10 mm) in length, but some deep sea species may reach a length of almost 2.4 in (6 cm). The body itself is usually quite small, the main mass of the spider being accounted for by its extremely long legs. The legs are attached to the anterior portion of the body (the prosoma) and are usually eight in number, although some species may have 10 or even 12 pairs. The body is segmented with the head bearing a proboscis for feeding, a pair of pincher like claws known as chelicera, and a pair of segmented palps that are sensory and probably assist with detecting prey. Most sea spiders are either a white color or the color of their background; there is no evidence that they can change their body coloration to match different backgrounds. Many deep sea species are a reddishorange color.

The majority of sea spiders crawl along the substrate in search of food and mates. They are often found attached to sea anemones, bryozoans, or hydra, on which they feed. They are all carnivorous species and feed by either grasping small prey with the chelicera, tearing off tiny polyps from corals or sponges, or by directly sucking up body fluids through the mouth, which is positioned at the extreme tip of the proboscis.

An unusual behavioral feature displayed by sea spiders is the males habit of looking after the eggs once they have been laid by the female. As the female lays her eggs, male fertilizes them and then transfers them to his own body. Here they are grouped onto a special pair of legs known as ovigerous legs (which are greatly enlarged in males). Large masses of eggs may be collectedoften as many as 1,000 on each leg. The male carries these egg clusters for several weeks until they hatch into tiny larvae that are known as a protonymphon. Even at this stage, some species continue to care for their offspring until they have further developed.

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Sea Spiders

Sea spiders

Sea spiders (phylum Arthropoda, class Pycnogonida) are a group of arthropods that take their common name from their superficial resemblance to the true spiders. Although rarely seen, these are widespread animals occurring in every ocean , with a preference for cooler waters. Sea spiders occupy a wide range of habitats: some species have been recorded from a depth of 19,685 ft (6,000 m), but the majority live in shallow coastal waters. Some 600 species have so far been identified.

Most sea spiders are small animals, measuring from 0.04-0.4 in (1-10 mm) in length, but some deep sea species may reach a length of almost 2.4 in (6 cm). The body itself is usually quite small, the main mass of the spider being accounted for by its extremely long legs. The legs are attached to the anterior portion of the body (the prosoma) and are usually eight in number, although some species may have 10 or even 12 pairs. The body is segmented with the head bearing a proboscis for feeding, a pair of pincher-like claws known as chelicera, and a pair of segmented palps that are sensory and probably assist with detecting prey . Most sea spiders are either a white color or the color of their background; there is no evidence that they can change their body coloration to match different backgrounds. Many deep sea species are a reddish-orange color.

The majority of sea spiders crawl along the substrate in search of food and mates. They are often found attached to sea anemones , bryozoans, or hydra , on which they feed. They are all carnivorous species and feed by either grasping small prey with the chelicera, tearing off tiny polyps from corals or sponges , or by directly sucking up body fluids through the mouth, which is positioned at the extreme tip of the proboscis.

An unusual behavioral feature displayed by sea spiders is the male's habit of looking after the eggs once they have been laid by the female. As the female lays her eggs, they are fertilized by the male who then transfers them to his own body. Here they are grouped onto a special pair of legs known as ovigerous legs (which are greatly enlarged in males). Large masses of eggs may be collected—often as many as 1,000 on each leg. The male carries these egg clusters for several weeks until they hatch into tiny larvae that are known as a protonymphon. Even at this stage, some species continue to care for their offspring until they have further developed-a strategy designed to protect the vulnerable offspring from the wide range of potential predators that exist in these waters.

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