Editing Seashell (section)

== Shells of other marine invertebrates ==
{{Unreferenced section|date=December 2017}}

=== Arthropods ===
[[File:Crab from Long Island.jpg|thumb|The moulted [[carapace]] of a [[lady crab]] found on the beach at [[Long Beach, New York|Long Beach, Long Island, New York State]]]]
[[File:Horseshoe Crab remains.jpg|thumb|left|Shell of [[horseshoe crab]] on a beach]]

Many [[arthropod]]s have [[sclerite]]s, or hardened body parts, which form a stiff exoskeleton made up mostly of [[chitin]].  In [[crustacean]]s, especially those of the class [[Malacostraca]] (crabs, shrimps and lobsters, for instance), the plates of the exoskeleton may be fused to form a more or less rigid [[carapace]]. Moulted carapaces of a variety of marine malacostraceans often wash up on beaches. The [[horseshoe crab]] is an arthropod of the family [[Limulidae]]. The shells or [[exuviae]] of these arachnid relatives are common in beach drift in certain areas of the world.

=== Echinoderms ===
[[File:Sea Urchin test 5629 03 22.jpg|thumb|[[Sea urchin]] test]]
Some [[echinoderm]]s such as [[sea urchin]]s, including [[heart urchin]]s and [[sand dollar]]s, have a hard "test" or shell. After the animal dies, the flesh rots out and the spines fall off, and then fairly often the empty test washes up whole onto a beach, where it can be found by a beachcomber. These tests are fragile and easily broken into pieces.

=== Brachiopods ===
[[File:LingulaanatinaAA.JPG|thumb|A whole animal of the brachiopod ''[[Lingula anatina]]'' from Australia with the shell showing on the left]]
The [[brachiopod]]s, or lamp shells, superficially resemble clams, but the phylum is not closely related to mollusks. Most lines of brachiopods ended during the [[Permian-Triassic extinction event]], and their ecological niche was filled by bivalves. A few of the remaining species of brachiopods occur in the low [[intertidal zone]] and thus can be found live by beachcombers.

=== Annelids ===
Some [[polychaetes]], marine annelid worms in the family [[Serpulidae]], secrete a hard tube made of calcium carbonate, adhering to stones or other shells. This tube resembles, and can be confused with, the shell of marine gastropod mollusks in the family [[Vermetidae]], the worm snails.