DESCRIPTION OF THE SUBPHYLUM MYRIAPODA (LATREILLE 1802)
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MYRIAPODA LINKS
| Myriapoda (mir-i-O-po-da) is formed from two Greek roots that mean “many feet” [myriad -myriada (μυριάδα); and feet -podi (πόδι)]. The reference is to many walking legs, one or two pairs of walking legs for most body segments. |
| INTRODUCTION TO THE MYRIAPODA The myriapods (millipedes, pauropods, centipedes, and symphylans; Figure 1, Clade 25) are similar in that they have a head and a long, multisegmented body, each with a pair of walking legs (the “segments” of the millipedes are fused pairs). Thus, their body is not separated into thorax and abdomen. The legs articulate with the sternum (text with tooltip) A sternum is the breastbone in vertebrates and the ventral plate of an arthropod body segment. by a single joint. They have Malpigian tubules (text with tooltip) Malpighian tubules are excretory organs in arthropods. They are fine tubules attached at the hind gut and bathed in the haemolymph (blood) of the haemocoel from which they remove nitrogenous waste. that likely are convergent, not homologous with those of the Hexapods. Almost all are terrestrial. The myriapods and hexapods have been lumped together in a group called the Uniramida (Barnes 1984; Willmer 1990) or Mandibulata (Margulis and Schwartz 1998), but the two groups do not seem to be part of a natural assemblage except within the phylum Arthropoda. Mallatt et al. (2004) confirm the monophyly of the myriopods by nearly complete 28S and 18S rRNA gene sequences. They also support the existence of a myriapod + chelicerate clade, a group that they call Paradoxopoda. However, structural synapomorphies have not been found that adequately unite these groups. Growing bodies of evidence confirm the monophyly of the Mandibulata with the Myriapoda as a basal group, and the topology of Figure 1 reflects the Mandibulata hypothesis (see the Arthropoda page). Since Regier et al. (2008), there has been consistent support for a mandibulate clade with the myriapods as a basal group (e.g. Rota-Stabelli et al. 2010, Regier and Zwick 2011, Oakley et al. 2012, and Misof et al. 2014). Developmental studies (e.g. Sharma et al. 2014) also support the Mandibulata hypothesis. |
 | MAJOR CLADES OF THE MYRIAPODA Ma = Mandibulata My = Myriapoda Pr = Progoneata Di = Dignatha |
| FIGURE 1. MAJOR CLADES OF THE MYRIAPODA. This is a portion of the Figure 2 on the Arthropoda page and the clade designations should refer back to that cladogram. | |
| Myriapod Clade (My) |
| Chilopoda The centipedes (Figure 2) are elongate, dorsoventrally flattened animals with numerous segments, each with 1 pair of legs. The head (or first trunk segment) bears one pair of large poison fangs on the undersurface. They have simple antennae and two pairs of maxillae. The eyes are simple, compound, or absent. The integument has no calcium carbonate. The last two segments are small and form pregenital and genital segments. The female has one ovary and one gonopore on the genital segment. The male has 1-24 testes and two gonopores on the genital segment. These animals are raptorial predators. |
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| FIGURE 2. A centipede. Note the obvious single pair of legs per segment. Image from http://www.ucmp.berkeley.edu/arthropoda/uniramia/myriapoda.html |
The Progoneata Clade (Pr)
Animals in this clade have the gonopores in anterior segments. The animals in this clade are detritivores. Gonopores occur anteriorly, usually at the third trunk segment.
- Symphyla
- Symphyla (Figure 3) are small, eyeless myriopods. The trunk has only 14 segments, the last fused to the telson. Each of the first twelve trunk segments has one pair of legs, the first pair being short. The penultimate segment has cerci and one pair of long sensory hairs. The dorsal surfaces of the segments are covered by 15-22 tergal plates. The antennae are long and thread-like and simple. Also, on the head, the second maxillae are fused. One pair of spiracles occur on the head, and their tracheae supply oxygen to the first three segments. Gonopores, which are found on the third trunk segment, are unpaired. Their integument is soft and uncalcified. The young hatch with six or seven pairs of legs and add new ones with successive molts. Symphylans also have a pair of silk glands.
- The Dignatha Clade (Di)
- These animals have only one pair of appendages on the head that are posterior to the mandibles. The gonopores are paired in most taxa. The spiracles open into a common tracheal pouch.
- Pauropoda (30)
- The pauropods (Figure 4) are small and blind. The mouth parts are poorly developed, but they include one pair of maxillae. The antennae are branched. The first trunk segment has no legs. Also, the animals have few tracheae. The trunk usually has twelve segments, and the central nine segments have one pair of legs each. They have some large tergal plates that extend over two segments and bear long tactile hairs. The integument is soft and uncalcified.
- Diplopoda (31)
- The millipedes (Figure 5) have what appears to be two pairs of legs per segment. Actually, their segments after the first four trunk segments, are fused into pairs of diplosegments, each with two pairs of legs. Also, each diplosegment is covered by a dorsal tergum. The first trunk segment is legless. They have simple seven-jointed antennae, and the maxillae are fused into a structure called a gnathochilarium. The integument normally is reinforced with calcium carbonate. Gonopores open on or near the coxae of the second pair of legs. The young usually hatch with three pairs of legs.
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| FIGURE 3. A photograph of a symphylan. Image from http://www.qvmag.tas.gov.au/zoology/multipedes/tassymph/symintro.html | FIGURE 4. A diagram of a pauropod. Note the branched antennae and the large tergal plates. Image from http://www.qvmag.tas.gov.au/zoology/multipedes/taspauro/pauintro.html | FIGURE 5. A millipede which shows the obvious two pair of legs per diplosegment. Image from http://www.ucmp.berkeley.edu/arthropoda/uniramia/myriapoda.html |
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| By Jack R. Holt and Carlos A. Iudica. Last revised: 02/05/2015 |
