Some mites prey on undesirable arthropods and are used in pest control, while others control
weed growth. Populations of whip scorpions are valuable in controlling populations of cock-
roaches and crickets. Finally, an unquantified, but major positive contribution of the mites
and ticks, as well as the centipedes and millipedes, is their role in ecosystems, especially
their roles as decomposers and the resulting enriching of the soil due to the release of the
nutrients during decomposition.
In the next lesson, we will discuss the diversity of insects. As we will see, insects, also
arthropods are beneficial in many ways, both to the ecosystems of which they are part, as
well as to humans.
Lesson Summary
- The phylum Arthropoda includes four living subphyla; chelicerates, including spiders,
mites, and scorpions; myriapods, including centipedes and millipedes; hexapods, in-
cluding insects; and crustaceans. Arthropods are characterized by a segmented body;
appendagesusedforfeeding,sensorystructures,defense,andlocomotion; adorsalheart
and a ventral nervous system; and a hard exoskeleton. Arthropods are the largest phy-
lum in the Animal Kingdom with more than a million described species; they are found
in all environments. There are a variety of respiratory systems in arthropods, including
gills, tracheal system, book lungs, and oxygen absorbing membranes; arthropods have
an open circulatory system and a complete digestive system. - Crustaceansconsistofalmost52,000species,themajorityofwhichareaquatic; theyare
amongthemostsuccessfulanimals. Therearesixclassesofcrustaceans, includingbrine
shrimp, barnaclesandcopepods, andthemalacostracans, includingcrabs, lobsters, and
shrimp. Centipedes and millipedes belong to the myriapods, where they occur most
abundantly in moist forests; they are chiefly nocturnal predators. - Arachnids are mainly terrestrial and comprise over 100,000 named species; adaptations
for a terrestrial existence include specialized respiratory structures, appendages modi-
fied for locomotion on land, internal fertilization, special sensory organs, and structures
for water conservation. Arachnids are divided into eleven subgroups, the most familiar
being spiders; spiders produce silk, which is used in a variety of ways. Many species of
crustaceans are used for food; some species of mites are used in pest control and for
controlling weeds; and centipedes, millipedes, and the acarines play a valuable role as
decomposers, enriching the soil as a result.
Review Questions
- What are arthropod appendages used for?
- What respiratory systems do terrestrial arthropods use?
- Arachnids have several adaptations for living on land. For each adaptation you list,
explain how it is beneficial for a terrestrial existence.