Phylum Arthropoda contains more known species than any other phylum. Scientists have identified more than 1,000,000 arthropod species, and some scientists expect there are millions yet to be identified. Arthropods are classified based on the number and structure of body segments and appendages.
Lobster
CRUSTACEA: Crustaceans
There are crustacean species in almost every habitat, but most are aquatic, and most of theseare marine. They have two or three body sections, two pairs of antennae, and chewing mouthparts called mandibles. Many have a carapace, or “shell,” that covers part or all of the body. Examples: crabs, lobsters, crayfish, pill bugs, water fleas, barnacles
CHELICERATA: Chelicerates
Living chelicerates include horseshoe crabs and arachnids. (Their extinct relatives include trilobites and giant “sea-scorpions.”) Most living chelicerates are terrestrial. The body is composed of two parts—the cephalothorax and abdomen. The first pair of appendages are specialized feeding structures called chelicerae. Chelicerates have no antennae.
Red Velvet Mite
Merostomata: Horseshoe crabs
The class Merostomata once included many species, but only four species of horseshoe crab survive today. All are marine. They have five pairs of walking legs and a long, spinelike tail.
Horseshoe crabs are actually more closely related to spiders than to crabs!
Arachnida: Arachnids
The vast majority of arachnids are terrestrial. They have four pairs of walking legs and no tail. Examples: spiders, ticks, mites, scorpions, daddy longlegs
Mexican Beauty Tarantula
Table of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis