Arthropoda

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 Phylum

 Subphylum

Class

MEROSTOMATA (Horseshoe crabs)

ARACHNIDA (Spiders, Ticks, Mites, Scorpions

PYCNOGONIDA (Sea spiders)

INSECTA (Insects)

CHILOPODA (Centipedes)

DIPLOPODA (Millipedes)

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<<<Merostomata

<<<Arachnida

<<<Chilopoda

Crustacea>>>

Insecta>>>

Diplopoda>>>

Because this phylum is arge, there are many ways of classifying it. Below is the most widely-accepted 4-subphylum method of dividing this phylum

(Spiders, Ticks, Mites, Scorpions)

(Horseshoe crabs)

NOTES

CHELICERATA (cheli = a claw, hoof)
Consists of arthropods that have 6 pairs of appendages, four of which are legs (or five in the case of the horseshoe crab). The first pair of appendages are modified as pincer-like mouthparts called chelicerae (these are the fangs in spiders).

CRUSTACEA (crusta = crust, rind)
This subphylum contains 30 000 species of arthropods that lead mostly aquatic lives. They have two pairs of antennae and mandibles.

UNIRAMIA:
These arthropods have one pair of antennae and one or two maxillae. They also have mandibles.

(Centipedes)

(Millipedes)

(Insects)

(Class Malacostraca in evidence, crabs)

Arthropoda

The phylum Arthropoda (from Greek árthron, "joint", and  podós "foot", which together mean "jointed feet"), is the largest and most successful of the animal phyla and includes insects, arachnids, millipedes, centipedes, crustaceans, and others. Arthropods have segmented bodies with appendages and show different patterns of segment fusion (tagmosis) to form integrated units.
Arthropods are characterized by their jointed limbs and cuticles, which are mainly made of a pretoein called chitin and other chemicals; the cuticles of crustaceans are also biomineralized with calcium carbonate, exctracted from the water. The cuticle protects the organs, gives support for the body, provides places for muscle attachment so allowing for efficient locomotion; it varies in the details of its structure, but generally consist of three main layers: the epicuticle, a thin outer waxy coat that moisture-proofs the other layers and gives them some protection; the exocuticle, which consists of chitin and proteins; and the endocuticle, which consists of chitin and other kind of proteins. The exocuticle and endocuticle together are known as the procuticle.
The cuticle is rigid and cannot stretch, thus  inhibiting growth's animal, for this reason it must periodically be shed to allow for the animal to grow. This stage is know as molting.