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Arthropod diversity

Phylum Arthropoda includes animals that have been successful in colonizing terrestrial, aquatic, and aerial habitats. The phylum is further classified into five subphyla: Trilobitomorpha (trilobites), Hexapoda (insects and relatives), Myriapoda (millipedes, centipedes, and relatives), Crustacea (crabs, lobsters, crayfish, isopods, barnacles, and some zooplankton), and Chelicerata (horseshoe crabs, arachnids, scorpions, and daddy longlegs). Trilobites are an extinct group of arthropods found from the Cambrian period (540–490 million years ago) until they became extinct in the Permian (300–251 million years ago) that are probably most closely related to the Chelicerata. The 17,000 described species have been identified from fossils ( [link] ).

The Hexapoda have six legs (three pairs) as their name suggests. Hexapod segments are fused into a head, thorax, and abdomen ( [link] ). The thorax bears the wings and three pairs of legs. The insects we encounter on a daily basis—such as ants, cockroaches, butterflies, and bees—are examples of Hexapoda.

The illustration shows the anatomy of a bee. The digestive system consists of a mouth, pharynx, stomach, intestine, and anus. The respiratory system consists of spiracles, or openings, along the side of the bee’s body that connect to tubes that run up and join a larger dorsal tube that connects all the spiracles together. The circulatory system consists of a dorsal blood vessel that has multiple hearts along its length. The nervous system consists of a cerebral ganglion in the head that connects to a ventral nerve cord.
In this basic anatomy of a hexapod, note that insects have a developed digestive system (yellow), a respiratory system (blue), a circulatory system (red), and a nervous system (purple).

Subphylum Myriapoda includes arthropods with legs that may vary in number from 10 to 750. This subphylum includes 13,000 species; the most commonly found examples are millipedes and centipedes. All myriapods are terrestrial animals and prefer a humid environment ( [link] ).

Photo a shows a light brown centipede with 15 pairs of long legs on the sides of the body. Photo b shows a black and red millipede with many pairs of little legs on the underside of the body.
(a) The centipede Scutigera coleoptrata has up to 15 pairs of legs. (b) This North American millipede ( Narceus americanus) bears many legs, although not one thousand, as its name might suggest. (credit a: modification of work by Bruce Marlin; credit b: modification of work by Cory Zanker)

Crustaceans, such as shrimp, lobsters, crabs, and crayfish, are the dominant aquatic arthropods. A few crustaceans are terrestrial species like the pill bugs or sow bugs. The number of described crustacean species stands at about 47,000. “Number of Living Species in Australia and the World,” A.D. Chapman, Australia Biodiversity Information Services, last modified August 26, 2010, http://www.environment.gov.au/biodiversity/abrs/publications/other/species-numbers/2009/03-exec-summary.html.

Although the basic body plan in crustaceans is similar to the Hexapoda—head, thorax, and abdomen—the head and thorax may be fused in some species to form a cephalothorax    , which is covered by a plate called the carapace ( [link] ). The exoskeleton of many species is also infused with calcium carbonate, which makes it even stronger than in other arthropods. Crustaceans have an open circulatory system in which blood is pumped into the hemocoel by the dorsal heart. Most crustaceans typically have separate sexes, but some, like barnacles, may be hermaphroditic. Serial hermaphroditism, in which the gonad can switch from producing sperm to ova, is also found in some crustacean species. Larval stages are seen in the early development of many crustaceans. Most crustaceans are carnivorous, but detritivores and filter feeders are also common.

Questions & Answers

How many bones are in the human skeleton
Treasure Reply
procce of digestion of proteins a long human alimentarycanal
Carson Reply
what are the properties of lipids?
Isiah Reply
They are: Fatty acids, fats, oils, waxes, phospholipid, glycolipids, steroids and some vitamins
explain why a fresh water fish excrete ammonia
Leonard Reply
plz answer my question
sorry i meant it has a nucleous unlike plant cells lol
Ammonia is the end product of protein catabolism and is stored in the body of the fish in high concentrations relative to basal excretion rates. Ammonia, if allowed to accumulate, is toxic and is converted to less toxic compounds or excreted
What are eukaryotic cells?
Nwosueke Reply
cell with no nucleous so not a plant cell
eukaryotic cells are membrane bound organelles that have a membrane bound nucleus
where does the cell get energy for active transport processes?
A'Kaysion Reply
IDK maybe glucose
what is synapsis
Adepoju Reply
how many turns are required to make a molecule of sucrose in Calvin cycle
Amina Reply
why Calvin cycle occurs in stroma
why do humans enhale oxygen and exhale carbondioxide?
Maryam Reply
why do humans enhale oxygen and exhale carbondioxide? For the purpose of breaking down the food
what is allele
uzoka Reply
process of protein synthesis
what is cell
Zulf Reply
a cell is a smallest basic, structural and functional unit of life that is capable of self replication
why does a fresh water fish excrete ammonia
plz answer my question
Ammonia is a toxic colorless gas and when its inside the fish biological system is converted to a less toxic compound then excreted in the form of urea. However too much ammonia will kill the fish " Ammonia Poisoning " which is a very common disease among fish.
what is cytoplasm
uzoka Reply
cytoplasm is fluid of cell.
how many major types of Cloning
Saeed Reply
comparative anatomy of gymnosperms?
Meenakshi Reply
anatomy of gymnosperms

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