CLASS DIPLOPODA (MILLIPEDES) (twofold + podus, foot)
The class Diplopada contains the millipedes. Ancestors of this group appeared during Devonian period. They were among the first terrestrial animals.
1. Metamerism: Millipedes have 11 to 100 trunk segments. These segments are formed by embryological fusion of primitive metameres. Two pairs of appendages are present on each trunk segment. Each segment is formed by the fusion of two segments. Fusion is also present internally. It is shown by two ganglia, two pairs of ostia and two pairs of tracheal trunks per apparent segment. Most millipedes are rounded in cross section. But some are more flattened.
2. Distribution and habitat: Millipedes are worldwide in distribution. They are found under leaf litter humus, or decaying logs. Their epicuticle does not contain much wax. Therefore, they live in a habitat which prevents desiccation. Their trunks have many legs. These legs simultaneously push against the substrate. It helps millipedes to move through the habitat.
3. Nutrition: Millipedes feed on decaying plant matter. They use their mandibles in a a chewing and scraping. The mouthparts of a few millipedes are modified for sucking plant juices.
4. Defense against predators: The desiccated or disturbed millipedes roll into a ball. Many millipedes also possess repugnatorial glands. They produce hydrogen cyanide. It repels other animals. Hydrogen cyanide destroys millipede tissues. Therefore, it is not synthesized and stored as hydrogen cyanide. Instead, a precursor compound and are released from separate glandular compartments. These are mix as they are millipedes are dropped unharmed due to repellants.
5. Reproduction: Male millipedes transfer sperm to female millipedes with gonopods or spermatophore. Gonopods is modified trunk appendage. Eggs are fertilized as they are laid. They are hatched in several weeks. Immature acquire more legs and segments with each molt.Finally, it becomes adult.