Metazoa		Myriapoda
ARTHROPODA		Myriapoda

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Myriapoda

ARTHROPODA |--Trilobita `--Euarthropoda |--Myriapoda | |--+--Symphyla | | `--+--Pauropoda | | `--Diplopoda | `--Chilopoda `--+--Chelicerata `--PANCRUSTACEA

Myriapoda   Phylogeny     Relationships with other main arthropod groups     Evolutionary History   Links

Myriapod cladogram, from Edgecombe, G. D. and Giribet, G., 2002

Myriapoda means 10,000 legs, which is taking poetic license.  But all myriapods do have elongated, many-segmented bodies and a large number of legs.  The body segments are not fused together and each has either one or two pairs of legs.  One pair of preoral antennae are present.  There is a single pair of mandibles and 1 or 2 pairs of maxillae (jaws).  Growth is anamorphic (i.e. adding segments and legs with successive molts).  The eyes (ocelli) are primitive. Reproduction is usually by indirect sperm transfer.  The uppermost segment (coxa pl: coxae) of each leg has a single articulation with the body. The Myriapoda were among the first animal life to colonize the land.  They are susceptible to desiccation, and so inhabit moist areas.  Usually nocturnal.

Relationships with other main arthropod groups

Many recent studies use molecular analysis to unite crustaceans with atelocerates (hexapods and myriapods) in the old established taxon Mandibulata, there are also many that align crustaceans with chelicerates and trilobites. Supporters of Mandibulata can't agree whether Atelocerata is monophyletic and sister to Crustacea (though this position has strong majority support), or whether crustaceans are sister to hexapods (Friedrich & Tautz, 1995; Dohle, 1998; Kraus, 1998), with the myriapods potentially paraphyletic (e.g., Averof & Akam, 1995).  Some molecular studies (e.g., Turbeville et al., 1991) have united the chelicerates with the myriapods, or with the crustaceans and insects to the exclusion of the myriapods.

Evolutionary History

Although myriapods clearly evolved from aquatic ancestors, there is no clear candidate known.  A tentative uniramian, Cambropodus gracilis, from the Middle Cambrian marine Wheeler formation of Utah, is rather centipede-like in appearance and may be a possible candidate, however the only known specimen is too fairly poorly preserved to tell.  Robison (1990).  

Myriapods were among the first animals to live a terrestrial lifestyle. According to Professor Greg Retallack, burrows in Ordovician paleosol (fossil soil) were made by millipedes or similar myriapods. By the late Silurian, Archipolypodans are well known, as well as possible Chilopoda (centipedes).

The Carboniferous was the golden age of Myriapods, with many large and small forms flourishing in the rich litter. The following illustration, from the Treatise of Invertebrate Paleontology, shows some representative species from the late Westphalian (Moscovian age) of Nyrany, drawn to scale (the largest, Acantherpestes gigas, is about 20 cm or more in length)

The most spectacular of all the myriapods were the giant Carboniferous Arthropleurida (up to 2 meters in length), but these were limited to the Euramerican coal swamps

The drying out of the tropical Carboniferous swamps during the Permian resulted in the end of the large myriapods, although small forms continue and have remained successful to this day.

Phylogeny

image right, alternative cladograms regarding myriapod and insect relationships, from  Edgecombe & Giribet (2002).

The following is modified from Edgecombe & Giribet (2002) to include three extinct taxa

<==o MYRIAPODA [Millipedia]
   `--o ?- †Cambropodus
      | ???-  †Euthycarcinida 
      |-- CHILOPODA 
      `--o PROGONEATA
         |-SYMPHYLA
         `--+- PAUROPODA 
            | ?- †ARTHROPLEURIDA
            `-- DIPLOPODA
                ` ?- †ARCHIPOLYPODA

Cambropodus gracilis has already been discussed. It is tentatively included here at the base of the myriapod family tree but remains problematic. Even more problematic are the uniramous euthycarcinoids. Concerning the relations of the remaining two extinct groups, the Archipolypoda and the Arthropleurida, remain controversial. Although both are often given their own class, the Archipolypoda are often classified under the Diplopoda (millipedes). Recent findings suggest that the Arthropleurida, despite their huge size and unique features, also be included among the millipedes. This explanation however fails to explain where aquatic forms like Eoarthrolpeura fit in (since no other aquatic myriapods are known)

Links

Links

Introduction to the Myriapoda

MYRIAPODA - brief lecture notes byJamie Seymour