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Phylum:  Arthropoda -- Insects, spiders, centipedes, crustaceans


    Subphylum:  Crustacea

        Class:  Branchiopoda – brine shrimp etc.

        Class:  Remipedia -- blind crustaceans

        Class:  Cephalocarida – horseshoe shrimp

        Class:  Maxillopoda – barnacles, fish lice, etc.

        Class:  Ostracoda – seed shrimp

        Class:  Malacostraca – lobsters, crabs, shrimp, etc


    Subphylum:  Trilobitomorpha

        Class:  Trilobita – trilobites (extinct)


    Subphylum:  Myriapoda

        Class:  Chilopoda – centipedes

        Class:  Diplopoda – millipedes

        Class:  Pauropoda -- related to centipedes

        Class:  Symphyla -- garden centipedes





 Subphylum:  Chelicerata

        Class:  Arachnida – spiders, scorpions, etc.

        Class:  Xiphosura – horseshoe crabs, etc.

        Class:  Pycnogonida – sea spiders

        Class:  Eurypterida – sea scorpions (extinct)


    Subphylum:  Hexapoda

        Class:  Insecta – insects

        Class:  Entognatha :  Collembola (springtails), Diplura

                       and Protura.


Bibliography      Citations




Sample Examinations          Invertebrate Classification




CLICK on underlined file names and included illustrations to enlarge:


          The Arthropoda is the most highly developed phylum of the invertebrates, and they contain the greatest number of species.  Included are such widely recognized groups as the insects, spiders, crabs and barnacles.


          General characteristics are a segmentation that varies in different parts of the body, often referred to as heteronomous metamerism.  There is a chitinous exoskeleton, which is flexible but horny and tough.  It is always mixed with other materials such as proteins and fats.  They all possess jointed appendages, one per segment, which are primitive and never fully functional.  The body cavity is a haemocoel that is not a true coelom.  There are a dorsal brain, ventral ganglia and nerve cord, and there is more nervous tissue in the head than in the Annelida.  They have three body regions, which may be combined.  The digestive tract is always of three parts:  (1) foregut, (2) mid gut and (3) hind gut.  The foregut and hindgut are of ectoderm derivation while the midgut is derived from mesoderm.  Molting is required as the cuticle is a non-growing part.




    The Subphylum:  Trilobitomorpha: Class:  Trilobita – are an extinct group since the Paleozoic that is studied because they were probably the most primitive of the Arthropoda.  Their body had a central region with a 3-lobed lateral area on either side.  They had a head and trunk and were flattened dorso-ventrally.  Compound eyes were present and one pair of appendages occurred on every segment of the body save the first.  Superficially they bore a close resemblance to the Branchiopoda and also to the Brachyura crabs.


          Trilobites were marine organisms and were numerous in the Cambrian and Silurian eras.  They were mostly quite small at about 5 centimeters, but one fossil of Terataspis sp. reached about 0.7 meters in length.  The anterior somites of a segmented trunk were movable on one another, while the most posterior segments were united to form a tagma known as the pygidium.  Their body could be rolled up like that of an Isopod.  It is thought that most species lived at the bottom of the ocean in shallow to moderately deep water.  However some species are believed to have been adapted to pelagic, burrowing and deep-sea environments.


          It is known that trilobites hatched as a larva, called the Protospis that was a bit circular and consisted mostly of a head. See Inv136 for example.





          Subphylum: Myriapoda, Class: Chilopoda includes the centipedes.  They are dorso-ventrally flattened.  Their body consists of a head and trunk but there is no thorax nor abdomen.  The head bears one pair of antennae, one pair of mandibles, one pair of maxillipedes with poison glands at the bases and ducts leading to pointed tips (Note:  these are absent in the Diplopoda).  There are two pairs of simple eyes called pseudocompound eyes.  They have maxillae on the 1st and 2nd segments.  The trunk bears uniramous appendages and there are 15 to 175 segments.  See examples at Inv141.



          Body Wall -- This consists of a cuticle, muscles and a haemocoel


          Digestive Tract -- A typical mouth to anus arrangement.


          Circulatory System -- The heart is tubular with one pair of ostia per segment.  The blood does not carry oxygen


          Respiration -- The tracheae are lined with ectoderm and cuticle, and heavy rings of cuticle line them.  They branch out and ultimately reach all tissues of the body.  The blood does not have an oxygen carrying function.


          Excretion -- Malpighian tubules are long, thread-like and blind-ending tubules.  They lie in the haemocoel and empty into the digestive tract at the junction of the mid and hindguts.  They extract nitrogenous wastes from the blood.


          Nervous System -- This system is the same as that found in the Crustacea.


          Reproduction -- The sexes are separate.  Genital organs are found at the posterior end of the body and development is direct.


          Locomotion -- These animals are fast movers.  Long posterior legs are sensory and used when moving backwards.


          Food & Digestion -- Chilopoda are carnivorous and their food is paralyzed first by the maxillipedes.




          Subphylum: Myriopoda, Class: Diplopoda includes the millipedes.  These are cylindrical animals with a head and trunk that is the same as in the Chilopoda.   The head appendages include antennae, mandibles, one pair of maxillae (instead of 2 pair as in the Chilopoda) and pseudocompound eyes on the head.  The trunk has 25-100 or more segments with each segment bearing two pair of appendages.  A fusion occurs between two segments all along the body except on the first trunk segment.  See example at Inv142.



          Reproduction -- Genital ducts open between the bases of the 2nd and 3rd legs.  This is anterior in contrast to the Chilopoda.


          Development -- it is essentially direct except that the first larva has only three pairs of legs with additions added later on.


          Food -- They are vegetarian animals that move very slowly and are harmless.









  Key References:     <medvet.ref.htm>    <Hexapoda>    [Additional references may be found at: MELVYL Library]


Akam, M.  2000.  Arthropods: Developmental diversity within a (super) phylum. Proceedings of the National Academy of Sciences (USA) 97: 4438-4441.

Averof, M. & M. Akam.  1995.  Insect-crustacean relationships: Insights from comparative developmental and molecular studies. Philosophical Trans. of the

       Roy. Soc., London B Biological Sciences 347: 293-303.

Briggs, D.E.G., & R.A. Fortey.  1989.  The early radiation and relationships of the major arthropod groups. Science 246 :241-243.

Briggs, D. E. G., R. A. Fortey & M. A. Wills.  1993.  How big was the Cambrian explosion? A taxonomic and morphologic comparison of Cambrian and Recent

      arthropods. Pages 33-44 in Evolutionary Patterns and Processes (D. R. Lees and D. Edwards, eds.) Linnean Society Symposium, Linnean Society of London.

Brusca, R. C.  2000.  Unraveling the history of arthropod diversification. Annals of the Missouri Botanical Garden 87: 13-25.

Brusca, R. C., & G. J. Brusca.  2003.  Invertebrates. 2nd Edition. Sinauer Publ., Sunderland, Massachusetts.

Chapman, A. D.  2009.  Numbers of Living Species in Australia and the World. 2nd edition. Australian Govt, Dept. of Environ., Water, Heritage & Arts. Canberra.

Chen, J. C., L. Ramsköld, & G. Zhou.  1994.  Evidence for monophyly and arthropod affinity of cambrian giant predators. Science 263:  1304-1308.

Cook, C. E., , Q. Yue, and M. Akam.  2005.  Mitochondrial genomes suggest that hexapods and crustaceans are mutually paraphyletic. Proc.Roy. Soc Series B

      272(1569): 1295-1304.

Dohle, W. 1997. Are the insects more closely related to the crustaceans than to the myriapods? Entomologia Scandinavica Suppl. 51: 7-16.

Edgecombe, G. D. (ed.).  1998.  Arthropod fossils and phylogeny. Columbia University Press, New York.

Edgecombe, G. D.  1998.  Devonian terrestrial arthropods from Gondwana. Nature 394: 172-175.

Edgecombe, G. D.,  G. Giribet, C. W. Dunn, A. Hejnol,  R. M. Kristensen,  R. C.  Neves,  G. W. Rouse,  K. Worsaae & M. V. Sřrensen.  2011.  Higher-level

      metazoan relationships: Recent progress & remaining questions. Organisms Diversity & Evolution 11(2): 151-172.

Greenberg, B.  1973.  Flies and Disease. Vol. 2. Biology and Disease Transmission. Princeton University Press, Princeton, NJ. 856 pp.

Hall, R.D., Gerhardt R. 2009. Flies (Diptera). In Mullen Gr, Durden LA (eds.), Med. & Vet. Entoml., 2nd Ed.. Elsevier, Burlington, MA. 637 pp.

Harrison, I.H, G. A. Da Silva, M. Pitman & D. W. Fleming, Vranjac A, Broome CV. 1989. Epidemiology and clinical spectrum of Brazilian purpuric fever. Journal

      of Clinical  Microbiology 27: 599-604.

Hinkle, N. C., P. J. Scholl, D. E. Mock & W. B. Warner.  2001.  Research & extension needs for integrated pest management for arthropods of veterinary importance.

      pp. 261-262. In Geden CJ, Hogsette JA (editors), Proceedings of a workshop in Lincoln, Nebraska. 2nd Ed. 328 pp

Janzen, J.-W. 2002. Arthropods in Baltic Amber. Ampyx-Verlag, Halle (Saale).

Matheson, R.  1950.  Medical Entomology.  Comstock Publ. Co, Inc.  610 p.

Müller, K. J. & D. Walossek.  1985.  A remarkable arthropod fauna from the Upper Cambrian "Orsten" of Sweden. Trans. Roy.Soc. Edinburgh: Earth

       Sciences 76: 161-172.

Peel, A. D., A. D. Chipman & M. Akam.  2005.  Arthropod segmentation: Beyond the Drosophila paradigm. Nature Reviews Genetics 6(12): 905-916.

Pisani, D., L.L. Polig, M. Lyons-Weiler & S. B. Hedges.  2004.  The colonization of land animals: molecular phylogeny and divergence times among arthropods.

       BMC Biol. 2(1).

Service, M.  2008.  Medical Entomology For Students.  Cambridge Univ. Press.  289 p

Legner, E. F.  1995.  Biological control of Diptera of medical and veterinary importance.  J. Vector Ecology 20(1): 59-120.

Legner, E. F.  2000.  Biological control of aquatic Diptera.  p. 847-870.  Contributions to a Manual of Palaearctic Diptera, Vol. 1, Science  Herald, Budapest.  978 p.

Schram, F. R. & R. A. Jenner.  2001.  The origin of Hexapoda: a crustacean perspective. Pages 243-264 in Proceedings of the International Symposium on the

      Origin of the Hexapoda. T. Deuve, ed. Annales de la Société entomologique de France 37.

Shear, W. A. & J. Kukalová-Peck.  1990.  The ecology of paleozoic terrestrial arthropods: the fossil evidence. Canadian Journal of Zoology 68: 1807–1834.

Tudge, C. 2000. The Variety of Life. Oxford: Oxford University Press.

Waloszek, D. & J. A. Dunlop.  2002.  A larval sea spider (Arthropoda: Pycnogonida) from the Upper Cambrian 'Orsten' of Sweden, and the phylogenetic position

      of pycnogonids. Palaeontology 45: 421-446.

Wheeler, W.C., P. Cartwright & C.Y. Hayashi.  1993.  Arthropod phylogeny: A combined approach. Cladistics 9: 1-39.



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