A seashell, also known as a sea shell, or simply as a shell, is the common name for a hard, protective outer layer, a shell (or in some cases a "test") that was created by a sea creature, a marine organism. The shell is part of the body of a marine animal. In most cases a shell is an exoskeleton, usually that of an animal without a backbone, an invertebrate.
- I have a large sea shell collection which I keep scattered on beaches all over the world. Maybe you've seen it.
- She sells sea-shells on the sea-shore;
The shells she sells are sea-shells I'm sure.
- One cannot collect all the beautiful shells on the beach. One can collect only a few, and they are more beautiful if they are few.
- Anne Morrow Lindbergh, Gift from the Sea (1955), p. 114.
- I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.
- Isaac Newton, reported in Sir David Brewster, Memoirs of the Life, Writings, and Discoveries of Sir Isaac Newton (1855), Volume II. Ch. 27.
- But I have sinuous shells of pearly hue
Within, and they that lustre have imbibed
In the sun’s palace-porch, where when unyoked
chariot-wheel stands midway in the wave:
Shake one, and it awakens; then apply
Its polisht lips to your attentive ear,
And it remembers its august abodes,
And murmurs as the ocean murmurs there.
- Walter Savage Landor, Gebir (1798), Book i.
Listening to seashells 
- Gather a shell from the strewn beach
And listen at its lips: they sigh
The same desire and mystery,
The echo of the whole sea's speech.
- Dante Gabriel Rossetti, The Sea-Limits, reported in Bartlett's Familiar Quotations, 10th ed. (1919).
- I send thee a shell from the ocean-beach;
But listen thou well, for my shell hath speech.
Hold to thine ear
And plain thou'lt hear
Tales of ships.
- Charles Henry Webb, With a Nantucket Shell, reported in Bartlett's Familiar Quotations, 10th ed. (1919).
- The hollow sea-shell, which for years hath stood
On dusty shelves, when held against the ear
Proclaims its stormy parent, and we hear
The faint, far murmur of the breaking flood.
We hear the sea. The Sea? It is the blood
In our own veins, impetuous and near.
- Eugene Lee-Hamilton, Sonnet. Sea-shell Murmurs, reported in Bartlett's Familiar Quotations, 10th ed. (1919).
- I have seen
A curious child, who dwelt upon a tract
Of inland ground, applying to his ear
The convolutions of a smooth-lipped shell;
To which, in silence hushed, his very soul
Listened intensely; and his countenance soon
Brightened with joy; for from within were heard
Murmurings, whereby the monitor expressed
Mysterious union with its native sea.
- Poor shell! that Wordsworth so pounded and flattened in his marsh it no longer had the hoarseness of a sea, but of a hospital.
- Walter Savage Landor, Letter to John Forster, reported in Bartlett's Familiar Quotations, 10th ed. (1919).