Sea Spiders
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Subphylum: Chelicerata Class: Pycnogonida Latreille, 1810 Order: Pantopoda
Families
may not be a complete list: Ammotheidae Austrodecidae Callipallenidae Colossendeidae Nymphonidae Phoxichilidiidae Pycnogonidae Rhynchothoracidae Endeididae Image File history File links Sea_spider. ... Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. ... Animalia redirects here. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Classes Arachnida- spiders, scorpions, etc. ... Pierre André Latreille. ... Genera Austrodecus Pantopipetta Austrodecidae is a family of sea spiders. ... Genera Colossendeis Hedgpethia Colossendeidae is a family of sea spider (class Pycnogonida). ... Genera Boreonymphon Heteronymphon Neonymphon Nymphon Pentanymphon Sexanymphon Nymphonidae is a family of sea spiders native to the Atlantic. ... Genera Anoplodactylus Halosoma Pallenopsis Phoxichilidium Phoxiphilyra Pycnosomia Phoxichilidiidae is a family of sea spiders. ...

Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. They are cosmopolitan, found especially in the Mediterranean and Caribbean Seas and the Arctic and Antarctic Oceans. There are approximately 1000 known species, ranging in size from 1-10 mm to over 90 cm in deep water species: most are toward the smaller end of this range, although in relatively shallow depths they grow to be the largest in Antarctica. Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... A cosmopolitan distribution is a term applied to a biological category of living things meaning that this category can be found anywhere around the world. ... Composite satellite image of the Mediterranean Sea. ... Map of Central America and the Caribbean A Caribbean beach in Isla Margarita, Venezuela. ... Arctic Region NASA Arctic sea ice imagery, 2005 The Arctic Ocean, located mostly in the Arctic north polar region, is the smallest of the worlds five oceans and the shallowest. ... The Southern Ocean is the body of water encircling the continent of Antarctica. ...

These small animals live in many different parts of the world, from Australia, New Zealand, and the Pacific coast of the United States to the Mediterranean and the Caribbean to the north and south poles. They are found in waters as deep as 7000 meters, but more commonly in shallower waters and in both marine and estuarine habitats. Although they are relatively common, Pycnogonids are well camouflaged beneath the rocks and among the algae that are found along shorelines. For other meanings of Pacific, see Pacific (disambiguation). ... The Mediterranean Sea is an intercontinental sea positioned between Europe to the north, Africa to the south and Asia to the east, covering an approximate area of 2. ... West Indian redirects here. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ...

Morphology

Their reduced body size is in contrast to their large, long legs. The number of their walking legs are usually four pairs, but species with five and six pairs exist. Because of their small size and slender body and legs, no respiratory system is needed for gas diffusion. A proboscis allows them to suck nutrients from soft bodied invertebrates, and their digestive tract has branches extending into their legs, known as diverticulae. The Respiratory System Among four-legged animals, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. ... In general, a proboscis (from Greek pro before and boskein to feed) is an elongated appendage from the head of an animal. ... Invertebrate is a term coined by Chevalier de Lamarck to describe any animal without a backbone or vertebra, like insects, squids and worms. ...

Pycnogonids are so small that each of their tiny muscles consists of only one single cell, surrounded by connective tissue. In terms of physical makeup, the proboscis, which has fairly limited dorso-ventral and lateral movement, and three to four appendages including the ovigers, which are used in caring for young and cleaning as well as courtship, are present in the anterior region. In some species, the chelifores, palps and ovigers can be reduced or missing in the adults. In those who lacks chelifores and palps, the proboscis is well developed and more mobile and flexible, often equipped with numerous sensory bristles and strong rasping ridges around the mouth. The last segment includes the anus and tubercle, which projects dorsally. This article is being considered for deletion in accordance with Wikipedias deletion policy. ... Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, muscle, and nervous tissue. ... A limb (from the Old English lim) is a jointed appendage of the human or animal branch of a tree; a representative, branch or member of a group or organization. ... This article or section does not cite its references or sources. ... Male European garden spider with swollen pedipalps Pedipalps are a pair of feelers on a spiders face. ... In general, a proboscis (from Greek pro before and boskein to feed) is an elongated appendage from the head of an animal. ... Female Human Anatomy Male Human Anatomy This article is about the bodily orifice. ...

In total, Pycnogonids have four to six legs for walking as well as other appendages which often resemble legs. A cephalothorax and much smaller abdomen make up the extremely reduced body of the Pycnogonid, which has up to two pairs of dorsally located simple eyes on its non-calcareous exoskeleton, though sometimes the eyes can be missing, especially among species living in the deep oceans. The abdomen does not have any appendages, and in most species it is reduced and almost vestigial. The organs of this fascinating chelicerate extend throughout many appendages because its body is too small to accommodate all of them alone. The cephalothorax is an anatomical term used of arachnid and malacostracan arthropods for the first major body section. ... The abdomen is a part of the body. ... An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animals body. ... Classes Arachnida- spiders, scorpions, etc. ...

The morphology of the sea spider creates a perfect surface-area to volume ratio for any respiration to occur through direct diffusion. The most recent research seems to indicate that waste leaves the body through the digestive tract or is lost during a molt. The small, long, thin pycnogonid heart beats vigorously at 90 to 180 beats per minute, creating substantial blood pressure. These creatures possess an open circulatory system as well as a nervous system consisting of a brain which is connected to two ventral nerve cords, which in turn connect to specific nerves.

Biology

Their habitats range from the shallow intertidal zones to deep water benthic environments, some 7000 metres down. Sea spiders do not swim but rather walk along the bottom with their stilt-like legs. Most are carnivorous and feed on cnidarians, sponges, polychaetes and bryozoans. In marine geology and biology, benthos are the organisms and habitats of the sea floor; in freshwater biology they are the organisms and habitats of the bottoms of lakes, rivers, and creeks. ... Classes Anthozoa - Corals and sea anemones Cubozoa - Sea wasps or box jellyfish Hydrozoa - Hydroids, hydra-like animals Scyphozoa - Jellyfish Cnidaria is a phylum containing some 10,000 species of relatively simple animals found exclusively in aquatic environments (most species are marine). ... Classes Calcarea Hexactinellida Demospongiae The sponges or poriferans (from the Greek poros pore and ferro to bear) are animals of the phylum Porifera. ... Subclasses Palpata Scoleoida Tomopteris from plankton The Polychaeta or polychaetes are a class of annelid worms, generally marine. ... Classes Stenolaemata Gymnolaemata Phylactolaemata Bryozoans are tiny colonial animals that generally build stony skeletons of calcium carbonate, superficially similar to coral. ...

Sea spiders are generally predators or scavengers. They crawl slowly along (although some do swim), feeding. They will often insert their proboscis, a long appendage used for digestion and sucking food into its gut, into a sea anemone and suck out nourishment. The sea anemone, relatively large in comparison to its predator, almost always survives this ordeal. Studies have shown that adult taste preferences depend on what the animals were fed as young. This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Categories: Stub ... Families Many, see text. ...

Subtaxa

The order Pycnogonida consists of approximately 1000 species, which are normally split into eighty-six genera. The correct taxonomy within the group is uncertain, and it appears that no agreed list of orders exists. Accordingly, families are listed in the table at the right. Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... In biological classification, family (Latin: familia, plural familiae) is 1) a rank or 2) a taxon in that rank. ...

Evolution and relationships

The evolutionary lineage of the sea spider group as a whole is disputed: their fossil record is sketchy at best, with the three earliest known genera originating in the Devonian. It has been suggested that this article or section be merged into Fossil. ... Disambiguation: Devonian is sometimes used to refer to the Southwestern Brythonic language, and the people of the county of Devon are sometimes referred to as Devonians The Devonian is a geologic period of the Paleozoic era. ...

Some believe (or once believed) sea spiders to be among the chelicerates, together with horseshoe crabs, true spiders, mites, ticks and scorpions. While sharing many morphological features with the other chelicerates, major differences (such as their unique proboscis) have caused many taxonomists to remove sea spiders from this grouping, and some consider them to form their own subphylum. Another reason for this is that it seems the appendages called chelifores are unique among present arthopods, and are not homologous to the chelicerae in real chelicerates as previously suspected. Instead of developing from the deuterocerebrum, they can be traced to the protocerebrum, the anterior part of the arthropod brain and found in the first head segment that in all other arthropods give rise to the eyes only. This is not found anywhere else among arthopods except in some fossil forms like Anomalocaris, indicating the Pycnogonida may be a sister group to all other living arthropods having evolved from some ancestor that had lost the protocerebrum appendages. If this is confirmed once and for all, it would mean the sea spiders are the last surviving (and highly modified) members of an ancient and long gone stem-group of arthropods that lived in the old Cambrian oceans. Classes Arachnida- spiders, scorpions, etc. ... Binomial name Limulus polyphemus Linnaeus, 1758 The horseshoe crab (Limulus polyphemus) is a chelicerate arthropod, therefore it is more closely related to spiders and scorpions than crabs. ... Diversity 111 families, 40,000 species Suborders Mesothelae Mygalomorphae Araneomorphae  See table of families Closeup image of a Wolf Spider Wikispecies has information related to: Spiders Spiders are predatory invertebrate animals that have two body segments, eight legs, no chewing mouth parts and no wings. ... Families Tetranychidae - Spider mites Eriophyidae - Gall mites Sarcoptidae - Sarcoptic Mange mites The mites and ticks, order Acarina or Acari, belong to the Arachnida and are among the most diverse and successful of all the invertebrate groups, although some way behind the insects. ... Families Ixodidae - Hard ticks Argasidae - Soft ticks Nuttalliellidae Wikispecies has information related to: Ixodoidea Tick is the common name for the small arachnids that, along with mites, constitute the order Acarina. ... Superfamilies Pseudochactoidea Buthoidea Chaeriloidea Chactoidea Iuroidea Scorpionoidea See classification for families. ... Subphyla and Classes Anomalocaridae - Anomalocarids, extinct     Genus Anomalocaris     Genus Laggania     Genus Parapeytoia Opabinidae - Extinct     Genus Opabinia Unclassified anomalocarid-like specimens     Genus Kerygmachela     Genus Pambdelurion Anomalocarids (meaning odd shrimp) are a group of very early marine animals known from fossils found in Cambrian deposits in China, North America, and Australia. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ...

In regard to the evolution of Pycnogonids, the fossil record is quite lacking, although two things are fairly clear: 1. Pycnogonids possessed a coelom at one point, but it was eventually lost through evolution, and 2. Pycnogonids are relatively old, with the earliest known genera placed in the Devonian period, between 416 and 355 million years ago.

A lucid view on relationships is given by Dunlop & Arango (2005), which treat the conflicting evidence for placing of the Pycnogonida 1) outside Arachnomopha as basal Euarthropoda, supporting the concept of Cormogonida (Euarthropoda excluding pycnogonids) or 2) inside Chelicerata (which is based only in the chelifore-chelicera putative homology). Classes Arachnida- spiders, scorpions, etc. ... 1 entry found for chelicerae. ... In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ...

Reproduction and development

All Pycnogonid species have two separate and different genders except for one species which is hermaphroditic. Females possess a pair of ovaries, while males possess a pair of testes located dorsally in relation to the digestive tract. Scientists are aware that reproduction involves external fertilization after “a brief courtship”, but very little is known about the secret lives of most Pycnogonids. Only males care for laid eggs and young. The larva has a blind gut and the body consist literally of a head and its three pairs of cephalic appendages only: the chelifores, palps and ovigers. The abdomen and the thorax with its thoracic appendages develops later. One theory is that this reflects how a common ancestor of all arthropods evolved; starting its life as a small animal with a pair of appendages used for feeding and two pairs used for locomotion, while new segments and segmental appendages were gradually added as it was growing. At least four types of larvae have been described: the typical protonymphon larva, the encysted larva, the atypical protonymphon larva, and the attaching larva. The typical protonymphon larva is most common, is free living and gradually turns into an adult. The encysted larva is a parasite that hatches from the egg and finds a host in the shape of a polyp colony where it burrows into and turns into a cyst, and will not leave the host before it has turned into a young juvenile. Not much is known about the development of the atypical protonymphon larva. The adults are free living, while the larvae and the juveniles are living on or inside temporary hosts such as polychaetes and clams. When the attaching larva hatches it still looks like an embryo, and immediately attaches itself to the ovigerous legs of the father, where it will stay till it has turned into a small and young juvenile with two or three pairs of walking legs ready for a free-living existence.

Trivia

David Staples, one of the few pycnogonid specialists in the world, notes, "An early researcher in the [study of Pycnogonids] was T.T. Flynn, father of actor Errol Flynn." Errol Flynn Errol Leslie Thomson Flynn (June 20, 1909 – October 14, 1959) was an Australian film actor, most famous for his romantic swashbuckler roles in Hollywood films and his flamboyant lifestyle. ...

Thomas Hunt Morgan, winner of the 1933 Nobel Prize in Physiology or Medicine, conducted his doctoral research on the development and evolution of Pycnogonida.

Reference

• Dunlop, J. A. & Arango, C. P. (2005). Pycnogonid affinities: a review. Journal of Zoological Systematics and Evolutionary Research, 43: 8-21.

• Maxmen, A., W.E. Browne, M.Q. Martindle, G. Giribet (2005). Neuroanatomy of sea spiders implies an appendicular origin of the protocerebral segment. "Nature", 437: 1144-1148.

External links

Wikispecies has information related to:

Pycnogonida

• Introduction to the Pycnogonida
• Images of Pycnogonida
• More Images of Pycnogonida

• Images of Pycnogonida, and Pycnogonids in literature