What characteristics distinguish arthropods from mollusks and worms?

Answer 1

The vertebral column or spine comprises individual bones (vertebrae) as part of an internal skeleton or endoskeleton. Arthropods differ in that they have no bony internal skeleton, instead they rely on an external or exoskeleton, whose rigidity creates the defining characteristics of the arhtropod phylum; the joint appendages and segmented body.

Answer 2

Phylum Arthropoda: Segmented bodies, an exoskeleton made from chitin, and joint appendages. Examples, insects, crustaceans, centipedes.

Phylum Mollusca: Muscular foot, mantle; examples-limpets, snails, slugs, octopi, bivalves.

Worms are tougher to broadly distinguish as they are classified into various phyla: Phylum Annelida, Chaetognatha, Entoprocta, Gnathostomulida, Hemichordata, Kinorhyncha, Nematoda, Nematomorpha, Nemertea, Onychophora, Phoronida, Platyhelminthes all answer to the description "worms". The earthworm we're most familiar with has a soft elongated segmented body with a round cross section, platyhelminthes are the flat-bodied worms often parasitic, and so forth. Some worms do evidence arthropod characteristics, for instance polychaetes exploit chitin.

Answer 3

One significant difference is the method used to facilitate gas exchange, for example to oxygenate tissues. Terrestrial arthropods have spiracles attached to tubules which conduct gas directly to and from the cells; aquatic arthropods have a gill system to extract oxygen from seawater. More obvious adaptations to the habitat are apparent, for example, to enable locomotion aquatic arthropods may have swimeretes (like shrimp); flight-capable terrestrial arthropods may have wings. Adaptations for the lower intensity light conditions in the marine environment are also apparent in the eye structures.

Answer 4

They usually have 3 body segments and jointed legs.

Answer 5

Vertebrates have a spine/backbone and mollusks and arthropods don't (they are invertebrates). See related questions below for more detail.