Flat-backed Millipedes
Polydesmida
Classification
- Phylum: Arthropoda
- Subphylum: Myriapoda
- Class: Diplopoda
- Order: Polydesmida
Pronunciation
How to pronounce Polydesmida: //ˌpɒl.iˈdɛz.mɪ.də//
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Images
Summary
The order Polydesmida consists of flat-backed millipedes, known for their unique morphology with flattened bodies, and their ability to produce hydrogen cyanide as a defense. With over 5,000 species, they play critical roles in their ecosystems as decomposers and show substantial morphological diversity. They are ubiquitous except in Antarctica, and exhibit a unique life cycle distinct from other milliped orders.
Physical Characteristics
Members of the order Polydesmida, or flat-backed millipedes, typically feature 3 to 130 mm in length and have 18 to 22 body rings (usually 20). They have pronounced lateral keels known as paranota, which provide a flattened appearance. Neonates hatch with 7 segments and grow by molting, generally attaining a fixed number of segments in adulthood, normally 20. Adults typically have 31 pairs of legs, but males have modified gonopods replacing one pair of legs. Bright coloration patterns are common in larger species, warning predators of their toxic secretions.
Identification Tips
Look for wide lateral keels called paranota that give them a flattened appearance; this distinguishes them from other millipede orders. They have no eyes, and their coloration can aid in warning predators.
Habitat
Polydesmida are commonly found in leaf litter, where they burrow by leveraging their bodies. They inhabit various terrestrial environments globally, except Antarctica.
Distribution
Polydesmida millipedes are found worldwide across various habitats, avoiding only Antarctica.
Diet
Their diet consists primarily of decaying vegetation, making them detritivores.
Life Cycle
Polydesmida undergo a developmental process termed teloanamorphosis, where they go through eight growth stages, starting with 7 segments and adding segments through molting until they reach a fixed adult form, without further molts afterwards.
Reproduction
Adults reproduce once they reach maturity, after which they die without another molt. They exhibit complex reproductive features, with males having gonopods and sexual dimorphism in some species.
Predators
Some species are preyed upon by funnel-web spiders.
Ecosystem Role
As detritivores, flat-backed millipedes play a crucial role in decomposition and nutrient cycling in their ecosystems.
Health Concerns
Some species produce cyanogenic compounds that can be converted into hydrogen cyanide as a defense against predators, which may pose a risk if handled improperly.
Collecting Methods
- Hand collection from leaf litter
- Using pitfall traps
Preservation Methods
- Ethanol fixation
- Drying and pinning for taxonomic study
Evolution
Polydesmida is the largest order of millipedes and the most morphologically diverse, encompassing a range of species from varying habitats and with a range of segment numbers and leg configurations.
Similar Taxa
Misconceptions
Some people may confuse flat-backed millipedes with centipedes, despite key differences in body structure and ecological roles.
Tags
- Polydesmida
- millipedes
- arthropods
- detritivores
- cyanogenic compounds