They don't have jointed legs or an exoskeleton. Arthropods are all armoured, leggy animals, such as centi/millipedes, crustaceans, arachnids and insects. Nothing wormy there, save for their larvae.
The clam worm does seem to have legs, but those are actually tufts of hair-like appendages, not true jointed arthropod legs.
An arthropod
Nope - it's a member of the Jellyfish family, not an arthropod.
Barnacles
although an octopus has eight arms or tantacles
An arthropod's main features are the segmented body, an exoskeleton made from chitin, and joint appendages.
An arthropod
Vectors of the arthropod.
As the arthropod grows up, the exoskeleton sheds in order for the arthropod to grow inside of it.
The Blowjob arthropod family
A crab is an arthropod.
arthropod
yes a beetle is an arthropod
You will see a clam.
a clam
No, the manila clam is saltwater.
It is a clam.
Yes, a moth is considered to be an arthropod.