Arthropod

Arthropods are invertebrates having a hard exoskeleton, a segmented body, and jointed appendages. The body is generally divided into three segments, 

Most arthropods lay eggs, which hatch into larvae. Some are viviparous, like scorpions, and bear live young. As most arthropods grow, they shed or molt their outer skin covering a number of times before becoming adults. There are some groups that metamorphose from larva to adult inside a cocoon or pupa of their own making. 

The phylum Arthropoda contains more species than any other group of organisms. There are over one million species described, and undoubtedly many more to be discovered. The phylum is divided into three subphyla trilobites, all of which are extinct, Chelicerata, which have no jaws or antennae, and Mandibulata, which have jaws and antennae. 

The Mandibulata is by far the largest group of arthropods, since it contains the insects. Animals in this group have two or three body segments, one or two pairs of antennae, and one pair of mandibles. The subphylum Mandibulata is divided into six classes, the largest two of which are the Hexapoda (insects) and Crustacea (crustaceans). 

Insects are typified by three main body segments, which are themselves further segmented, antennae, mandibles, three pairs of legs, two pairs of wings, and compound eyes. There is incredible diversity in this huge group and body types and sizes vary greatly. 

Advances in Chemistry American Chemical Society Washington, DC, 1966. 

Although the boll weevil, a very serious cotton pest in the South, feeds voraciously on cotton squares and bolls in response to an at-tractant or attractants contained therein, these same cotton parts (49) contain also a boll weevil repellent that shows its effect once the at-tractant has volatilized completely. Department of Agriculture scientists are attempting to isolate and identify this repellent, which presumably could be applied to ward off weevil attack. Cotton seedlings painted with an aqueous emulsion of the material effectively repelled 100% of the weevils for 5 hours and only medium damage was evident after 12 hours, whereas control seedlings were completely destroyed after only 2 hours. 

Repellency appears to be associated with the highly pungent odor of the material since physical contact is unnecessary. The oily repellent is stable to heat and is not phytotoxic to the seedlings when proper aeration is provided. 

Oysters may be one of the best-known bivalves along the coast. An oyster cements one valve to a rock or other solid substrate and spends its entire life in that place. Oyster shells are heavy rough, and variable in shape. Unlike most other bivalves, the oyster lacks a foot and siphons, so must open its shell to circulate water over its gills. The common oyster (Crassostrea vir-ginica), like those seen in the lower color insert on page C-4, is found along much of the eastern coast of North America. 

Arthropods make up an extremely large group of animals in the intertidal zone. Their terrestrial cousins are the familiar, ever-present insects and spiders. Along the coast, typical marine arthropods include crabs, shrimp, lobsters, and horseshoe crabs. 

The body of an arthropod is covered with a hard shell called the exoskeleton, which provides structural support and protection from predators. The skeletons of arthropods are primarily composed of chitin, an extremely tough but highly flexible material made of long chains of molecules that are similar in structure to cellulose. 

Soldier crabs (Mictyris longicarpus) accumulate copper mostly from sediments rather than the water column. The fine particles of sediment trapped as food contain bioavailable fractions of copper and other metals, and these significantly correlate with metal concentrations in the body of the crab. However, copper accumulations from sediments by soldier crabs occur only at an artificially high concentration (1900.0 mg Cu/kg DW sediment), which also had toxic effects. Soldier crabs seem unable to regulate copper within their body. 

In shore crabs, several days of exposure to sublethal concentrations of waterborne copper cause extensive damage to gill epithelium at lethal concentrations, tissue hypoxia 

In the rasty crayfish (Orconectes rusticus), toxicity of copper at high concentrations is due to the coagulatory action on cellular proteins and the interference with respiratory processes at low concentrations, copper causes degenerative changes in certain tissues and interferes with glutathione equilibrium. Larvae of the red crayfish (Procambarus clarkii) exposed to copper as embryos are less sensitive than those exposed after hatching, suggesting acclimatization. 

Meade et al. [24] reported the responses of heat and oxygen flux to varying levels of environmental oxygen for the Australian crayfish Che rax quadricarinatus. When crayfish were exposed to p y2 values less than approximately 5 kPa, both heat dissipation and oxygen uptake were depressed. However, the depression of heat dissipation was only transient, and it recovered to normoxic values within 4 h, which suggested some form of metabolic compensation. CR ratios at or below the critical Pq2 were not determined, so the quantitative contribution of anaerobic pathways to any compensation could not be estimated. These juvenile crayfish were incapable of surviving a 1-2 h anoxic treatment at 28 C. 

---

Insect Growth Regulators. These compounds (40—45), unlike most conventional insecticides, interfere with biochemical processes that are unique to arthropods eg, molting, ecdysis, and formation of the chitinous exoskeleton. Therefore, they are selective insecticides with very low mammalian toxicity. 

R. T. Roush and B. E. Tabashnik, eds.. Pesticide Resistance in Arthropods, Chapman Hall, New York, 1990. 

G. P. Georghiou and A. Lagunes-Tejeda, The Occurrence of Resistance to Pesticides in Arthropods, FAO, Rome, 1991. 

Repellents Not Using Human Bait (No Attractant). A treated strip of fabric and a control strip are lowered iato a container of crawling arthropods such as ticks, fleas, and mites. After a predetermined time, the strips are lifted, the animals remaining are counted, and the percentage repeUency is determined. 

Repellents Tested with Animal Attractants. Numerous methods have iavolved the use of animals as attractants, foUowed by evaluation of repeUents as skin treatments or attached cloth treatments, often against crawling arthropods such as fleas, ticks, and mites. Animals such as gerbUs, guiaea pigs, camels, mice, shaved rabbits, and hairless dogs have been used, particularly when the toxicity is unknown. 

The treatment of Semliki Forest, San Angelo, and benzi vimses in mice suggests 7- thia-8-oxoguanosiae (59) may be useful in treating arthropod-home diseases that are endemic to Asia, the Pacific, and Africa. 

Animals, including insects and other arthropods or brewing, fish, silk and leather industries Research and educational laboratories, pest control... 

Arthropod Invertebrate with jointed body and limbs (includes insects, arachnids, and crustaceans). 

The phylum Arthropoda includes the classes Diplopoda (millipedes), Chilopoda (centipedes), Crustacea (see Chapter 3), and Insecta (see Chapter 1). All luminous arthropods other than crustaceans are terrestrial, and not very many luminous millipedes and centipedes are known. The luminescence of millipedes is usually intracellular, whereas luminous centipedes discharge luminous secretion. Substantial chemical studies have been made only with the millipede Luminodesmus sequoiae and the centipede Orphaneus brevilabiatus, of which the latter is discussed in the Section 10.3. 

An excellent review by Roth and Eisner (63) summarized the chemical defense substances found in arthropods up to 1962. These authors listed 31 defense substances of known structure one anhydride, three carboxylic acids, nine aldehydes, one furan, three hydrocarbons, two ketones, one lactone, eight quinones, and three inorganic compounds. Many of these same compounds (unsaturated aldehydes and quinones) have been found in other arthropods since 1962 (38). The compounds are discharged when the animal is disturbed by predators, and there can be no doubt that the action of most of them... 

Copper is essential in animal metabolism. In some animals, such as the octopus and certain arthropods, it transports oxygen through the blood, a role performed by iron in mammals. As a result, the blood of these animals is green rather than red. In mammals, copper-bearing enzymes are necessary for healthy nerves and connective tissue. 

Richards AG (1951) The Integument of Arthropods. Univ Minnesota Press, Minneapolis... 

Neville AC (1975) Biology of the Arthropod Cuticle. Springer-Verlag, Berlin Heidelberg New York... 

Dennehy, T. J. Hoffman, C. J. Nyrop, J. P. Saunders, M. C. In Monitoring and Integrated Management of Arthropod Pests of Small Fruit Crops, Intercept London, 1990 pp. 261-282. 

Silurian 440 Myr Sea levels rise, two large continents form, hothouse climate. Diversification of jawless fishes, first bony fishes invasion of land by vascular plants and arthropods... 

Paetzold A, Bemet J, Tockner K (2006) Rapid response of riparian arthropods to aquatic subsidy pulses. Freshw Biol 51 1103-1115... 

Arthropod-borne vims infections Under investigation Kafil et al. 2005 Lewis and Amsden 2007 Rahal et al. 2004 Solomon et al. 2003... 

One other biotransformation deserving mention is the oxidation of p,p -DDT to kelthane, a molecule that has been used as an acaricide. This biotransformation occurs in certain DDT-resistant arthropods, but does not appear to be important in vertebrates. 

Pyrethroids, such as p,p -DDT, are toxic because they interact with Na+ channels of the axonal membrane, thereby disturbing the transmission of nerve action potential (Eldefrawi and Eldefrawi 1990, and Chapter 5, Section 5.2.4 of this book). In both cases, marked hydrophobicity leads to bioconcentration of the insecticides in the axonal membrane and reversible association with the Na+ channel. Consequently, both DDT and pyrethroids show negative temperature coefficients in arthropods increasing temperature brings decreasing toxicity because it favors desorption of insecticide from the site of action. 

Pyrethroids show very marked selective toxicity (Table 12.2). They are highly toxic to terrestrial and aquatic arthropods and to fish, but only moderately toxic to rodents, and less toxic still to birds. The selectivity ratio between bees and rodents is 10,000- to 100,000-fold with topical application of the insecticides. They therefore appear to be environmentally safe so far as terrestrial vertebrates are concerned. There are, inevitably, concerns about their possible side effects in aquatic systems, especially on invertebrates. 

---