How many classes arthropods?

Answer 1

Phylum Arthropoda hosts at least eighteen classes, (not counting those yet to be fully classified):

Trilobita - trilobites (extinct)

Arachnida - Spiders, scorpions, etc.

Merostomata - horseshoe crabs, eurypterids (extinct), etc.

Pycnogonida - sea spiders

Chilopoda - centipedes

Diplopoda - millipedes

Pauropoda - sister group to millipedes

Symphyla - resemble centipedes

Branchiopoda - brine shrimp etc.

Remipedia - blind crustaceans

Cephalocarida - horseshoe shrimp

Maxillopoda - barnacles, copepods, fish lice, etc.

Ostracoda - seed shrimp

Malacostraca - lobsters, crabs, shrimp, etc.

Insecta - insects

Entognatha - wingless

Camptophyllia (extinct)

Marrellomorpha (with one extinct species)

Answer 2

Under phylum arthropoda are several subphyla, below which there are at least 18 classes, viz:

Trilobita - trilobites (extinct)

Arachnida - spiders, scorpions, etc.

Merostomata - horseshoe crabs, eurypterids (extinct), etc.

Pycnogonida - sea spiders

Chilopoda - centipedes

Diplopoda - millipedes

Pauropoda - sister group to millipedes

Symphyla - resemble centipedes

Branchiopoda - brine shrimp etc.

Remipedia - blind crustaceans

Cephalocarida - horseshoe shrimp

Maxillopoda - barnacles, copepods, fish lice, etc.

Ostracoda - seed shrimp

Malacostraca - lobsters, crabs, shrimp, etc.

Insecta - insects

Entognatha - wingless

Camptophyllia (extinct)

Marrellomorpha (with one extinct species)

Note that the taxonomic rank of some may be different depending on the text consulted (sometimes the distinction of subphylum, class, and subclass may blur); and that some are still being debated or of uncertain classification.

Answer 3

Arthropoda are generally considered to be one of about 35 phyla. Below (beneath) the phylum arthropoda (arthropods) are two clades, Chelicerata (which includes the arachnids) and Mandibulata (which includes crustaceans and insects). Properly speaking below those are subphyla and beneath those are the taxonomic entity properly called a "Class" of which there are dozens under the arthropod "umbrella". Note that there does linger some debate on the taxonomic classification system and sometimes the distinction between clades, subphyla and classes tends to blur.