? Chelicerata
Sea Spider
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Subphylum: Chelicerata Heymons, 1901
Classes
Arachnida- spiders, scorpions, etc. Merostomata- Horseshoe crabs, etc. Pycnogonida- sea spiders

The Subphylum Chelicerata constitutes one of the major subdivisions of the Phylum Arthropoda, including the arachnids, horseshoe crabs, and related forms. These mainly predatory arthropods outlasted the now extinct trilobites, the common marine arthropod of the Cambrian era. Most of the marine chelicerates, including all of the eurypterids, are now extinct. Image File history File links Sea_spider. ... Families may not be a complete list: Ammotheidae Austrodecidae Callipallenidae Colossendeidae Nymphonidae Phoxichilidiidae Pycnogonidae Rhynchothoracidae Endeididae Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms (as opposed to folk taxonomy). ... Phyla Subregnum Parazoa Porifera (sponges) Subregnum Agnotozoa Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (dicyemids) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to flatworms, echinoderms, etc. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Orders Acarina Amblypygi Araneae Opiliones Palpigradi Pseudoscorpionida Ricinulei Schizomida Scorpiones Solifugae Uropygi The arachnids, Arachnida, are a class of invertebrate animals in the subphylum Chelicerata. ... Suborders Araneomorphae Mesothelae Mygalomorphae See the taxonomy section for families Spiders are invertebrate animals that produce silk, and have eight legs and no wings. ... Superfamilies Pseudochactoidea Buthoidea Chaeriloidea Chactoidea Iuroidea Scorpionoidea See classification for families. ... Orders †Order Eurypterida Order Xiphosura Merostomata is a class of marine arthropods which includes horseshoe crabs and eurypterids. ... Binomial name Limulus polyphemus Linnaeus, 1758 The horseshoe crab (Limulus polyphemus) is an arthropod that is more closely related to spiders than crabs. ... Families may not be a complete list: Ammotheidae Austrodecidae Callipallenidae Colossendeidae Nymphonidae Phoxichilidiidae Pycnogonidae Rhynchothoracidae Endeididae Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. ... Families may not be a complete list: Ammotheidae Austrodecidae Callipallenidae Colossendeidae Nymphonidae Phoxichilidiidae Pycnogonidae Rhynchothoracidae Endeididae Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Orders See text. ... Binomial name Limulus polyphemus Linnaeus, 1758 The horseshoe crab (Limulus polyphemus) is an arthropod that is more closely related to spiders than crabs. ... This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Proetida Asaphida Harpetida Ptychopariida doubtful order Nektaspida Trilobites are extinct arthropods in the class Trilobita. ... The Cambrian is a major division of the geologic timescale that begins about 542 Ma (million years ago) at the end of the Proterozoic eon and ended about 488. ... Orders many, all extinct The eurypterids were the largest known arthropods that ever lived. ...

In the Chelicerata, the body is divided into an anterior prosoma (or cephalothorax) composed of eight segments plus a presegmental acron and a posterior opisthoma (or abdomen) composed of twelve segments plus a postsegmental telson. As in other arthropods the mouth lies between the second and third segments, but whereas in other groups there is usually a pair of antennae on the last preoral segment, here there are none. The prosoma usually has eyes. The appendages on the segments of the prosoma are as follows: In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... The cephalothorax is an anatomical term used of arachnid and malacostracan arthropods for the first major body section. ... The English word POSTERIOR is identical to the original Latin adjective, and has two different uses : as an ADJECTIVE, it indicates that someone or something is behind another, either spatially or chronologically it also became a SUBSTANTIVE, indicating the rear-end, especially of a person, i. ... Opisthoma Definition A section of an insects body when touched, explodes and sterilizes the female during mating. ...

1. None
2. None
3. Chelicerae (pincers)
4. Legs or pedipalps
5. Legs
6. Legs
7. Legs
8. Legs

The chelicerae, which give the group its name, are pointed appendages that grasp the food in place of the chewing mandibles most other arthropods have. Most are unable to ingest anything solid, so they drink blood or spit or inject digestive enzymes into their prey. The legs on the prosoma are either uniramous or have a very reduced gill branch, and are adapted for walking or swimming. The appendages on the opisthoma, in contrast, are either absent or are reduced to their gill branch. The Chelicerata are divided into four classes: The chelicerae of spiders are the mouth parts from which the fangs extend. ... Male European garden spider with swollen pedipalps Pedipalps are a pair of feelers on the front end of a spiders prosoma (aka cephalothorax), which can be thought of as its head. ... Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... The limb of an arthropod is said to be uniramous when it has only one branch. ... gills of a Smooth Newt Gills inside of a tuna head In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. ...

• Arachnida (spiders, scorpions, mites, etc.)
• Xiphosura (horseshoe crabs)
• Eurypterida (extinct sea scorpions)
• Pycnogonida (sea spiders)

Yellow mite
Lorryia formosa

underside of a dead female horseshoe crab

The Pycnogonida actually show some strong differences from the body plan described above, and it has been suggested that they represent an independent line of arthropods. They may have diverged from the other chelicerates early on, or represent highly modified forms. Sometimes they are excluded from the Chelicerata but grouped with them as the Cheliceriformes. The name Merostomata should be avoided because in all recent cladistic hypotheses it refers to a paraphyletic group composed by the Xiphosura + Eurypterida. Orders Acarina Amblypygi Araneae Opiliones Palpigradi Pseudoscorpionida Ricinulei Schizomida Scorpiones Solifugae Uropygi The arachnids, Arachnida, are a class of invertebrate animals in the subphylum Chelicerata. ... Suborders Araneomorphae Mesothelae Mygalomorphae See the taxonomy section for families Spiders are invertebrate animals that produce silk, and have eight legs and no wings. ... Superfamilies Pseudochactoidea Buthoidea Chaeriloidea Chactoidea Iuroidea Scorpionoidea See classification for families. ... 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. ... Orders see text Merostomata is a class of marine arthropods which includes horseshoe crabs and eurypterids. ... Binomial name Limulus polyphemus Linnaeus, 1758 The horseshoe crab (Limulus polyphemus) is an arthropod that is more closely related to spiders than crabs. ... Orders many, all extinct The eurypterids were the largest known arthropods that ever lived. ... Orders many, all extinct The eurypterids were the largest known arthropods that ever lived. ... Families may not be a complete list: Ammotheidae Austrodecidae Callipallenidae Colossendeidae Nymphonidae Phoxichilidiidae Pycnogonidae Rhynchothoracidae Endeididae Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. ... Families may not be a complete list: Ammotheidae Austrodecidae Callipallenidae Colossendeidae Nymphonidae Phoxichilidiidae Pycnogonidae Rhynchothoracidae Endeididae Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. ... Image File history File links Download high resolution version (1800x2400, 4177 KB) Historically, mites have been difficult to study because of their minute size. ... Image File history File links Download high resolution version (1800x2400, 4177 KB) Historically, mites have been difficult to study because of their minute size. ... Dead female horseshoe crab from NOAA Photo Library: Image ID: line2632, Americas Coastlines Collection Location: Patuxent River, Maryland Photo Date: 2002 August 17 Photographer: Mary Hollinger, NESDIS/NODC biologist, NOAA File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old... Dead female horseshoe crab from NOAA Photo Library: Image ID: line2632, Americas Coastlines Collection Location: Patuxent River, Maryland Photo Date: 2002 August 17 Photographer: Mary Hollinger, NESDIS/NODC biologist, NOAA File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old... Orders †Order Eurypterida Order Xiphosura Merostomata is a class of marine arthropods which includes horseshoe crabs and eurypterids. ...

Sanctacaris, and perhaps the aglaspids, may also belong here. These are extinct forms found in Cambrian rocks. After them, the oldest group of chelicerates are the Eurypterida, found from the Ordovician onwards. When young, these show a resemblance to the trilobites, suggesting a possible relationship between these two groups. Sanctacaris is a Middle Cambrian arthropod from the Burgess shale of British Columbia. ... The Cambrian is a major division of the geologic timescale that begins about 542 Ma (million years ago) at the end of the Proterozoic eon and ended about 488. ... Orders many, all extinct The eurypterids were the largest known arthropods that ever lived. ... The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ... Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Proetida Asaphida Harpetida Ptychopariida doubtful order Nektaspida Trilobites are extinct arthropods in the class Trilobita. ...