What are some similarities and differences between are mollusks and arthropods

Please help I have a Science test tomorrow!

Mollusks are triplobastic - they have an ectoderm layer (outer layer), mesoderm layer (middle layer), endoderm layer (inner layer). They are protosomes! - so they have spiral cleavage. They don't shed their skin!! They have a coelom!! (Body cavity) They are bilaterial!

Mollusks - triploblastic, protosomes, bilaterial symmetry, don't have special appendages - or joined, they don't shed their skin! (lophotrochochozoan.)
Arthropods - triploblastic, protosomes, bilaterial symmetry, they have special appendages! they shed their skin (ecdysozoa!)

An arthropod is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages. Arthropods are members of the Phylum Arthropoda (from Greek ἄρθρον arthron, "joint", and ποδός podos "foot", which together mean "jointed feet"), and include the insects, arachnids, crustaceans, and others
The Mollusca, common name molluscs or mollusks,[note 1] is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. This is the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. Molluscs are highly diverse, not only in size and in anatomical structure, but also in behaviour and in habitat.....!!