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The question might presume facts not in evidence. A sea shell itself is not a living thing but a structure, outgrowth, or excretion of a marine mollusc (pylum Mollusca) and by definition a different phylum from the arthropods (phylum Arthropoda). Having said that, there is at least one crustacean (grouped under arthropods), the hermit crab, which exploits discarded sea shells for purposes of protection.
In a loose sense, the exoskeleton of marine organisms like the crab or lobster (both arthropods) might be termed 'shells', and the answer to why the shell is so located might be, both to provude structural integrity (having no internal skeleton) and, like molluscs, for defense (armor).
What else can I help you with?
Are worms an arthopod?
No, worms are not arthropods because they do not have a shell. All arthropods have an external shell or an exoskeleton which is used to define them or classify them.
What things live in the ordovician period?
Primitive arthropods, fish, orthocones and sea scorpiond.
What has a shell and doesn't live in the sea?
A snail. A tortise.
Is a cobra an mollusk?
A mollusk is a sea creature that lives within a shell. A cobra does not live in a shell.
Are insects and spiders and crabs arthropods?
Yes. Anything with an exoskeleton or a hard shell (except turtles) are arthropods.
How long does a sea shell live?
Sea shells do not live; they are the external skeletons of marine mollusks. The lifespan of the mollusk that created the shell varies depending on the species, but it can range from a few years to several decades.
The shell-like structure that encases the bodies of arthropods?
exoskeleton
How long do cockles live?
cockles live at the beach and they are a type of shell that can sometimes have a sea creature living in them
Is a sea urchin a arthropod?
No. Sea urchins are echinoderms, meaning, appropriately enough, "spiny skin". Some of the characteristics of arthropods are jointed appendages, an exoskeleton, and a segmented body. While the hard test, or shell, of sea urchins could be thought of as an exoskeleton, sea urchins have no jointed appendages and do not have a segmented body. Some examples of arthropods are shrimps, crabs, lobsters, and insects.
What is the difference between an arthropod and a echinoderm?
Echinoderms are mostly marine while arthropods dwell in almost all habitats.
Arthropods have an exoskeleton a rigid external shell made of a substance called?
Chitin
What sounds do sea shell make?
What is the sound in a sea shell
