die Muschel
shell
The hard shell of a mollusk, often consisting of two parts, that is frequently found on the beach.
Die Kinder sammelten am Strand bunte Muscheln und Steine.
The children collected colorful shells and stones on the beach.

shell / mussel
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shell
The hard shell of a mollusk, often consisting of two parts, that is frequently found on the beach.
Die Kinder sammelten am Strand bunte Muscheln und Steine.
The children collected colorful shells and stones on the beach.

'Muschel' sounds similar to the English word 'muscle', but it means 'shell' or 'mussel'. The German word for 'muscle' is 'der Muskel'. This mix-up is a common mistake.
Nach dem Sport tut mir jeder Muskel weh.
After exercising, every muscle hurts.
Whether the shell or the animal is meant is usually revealed by the verb. 'Muscheln sammeln' (to collect shells) refers to the empty shells on the beach, while 'Muscheln essen' (to eat mussels) or 'kochen' (to cook) refers to the animal as food.
Wir haben am Strand schöne Muscheln gesammelt.
We collected beautiful shells on the beach.
When referring to the ear, the compound word 'die Ohrmuschel' (outer ear) is almost always used. The word 'Muschel' (shell/mussel) on its own is very rare in this context and could be misunderstood.
Er trug einen Ohrring in seiner linken Ohrmuschel.
He wore an earring in his left outer ear.
The meaning referring to a telephone receiver is dated. It refers to old rotary phones, where the receiver consisted of a mouthpiece and an earpiece.
Meine Oma erzählte, wie man früher die Muschel ans Ohr halten musste.
My grandma told me how people used to have to hold the earpiece to their ear.
ear
'das Ohr' and 'die Muschel' can both refer to a part of the ear. 'Ohr' is the general word for the whole hearing organ. In this context, 'Muschel' refers more specifically to the 'Ohrmuschel' (outer ear / auricle), that is, the outer, visible part of the ear. The words can be confused because in everyday speech people often simply say 'Ohr', even when only the outer part is meant. 'Muschel' sounds more precise and more medical or descriptive; outside this context, 'Muschel' usually means something from the beach or an animal in the water.

Die Ärztin untersucht die Muschel des Ohres auf eine kleine Verletzung.
The doctor examines the outer part of the ear for a small injury.
Beim Arzt zeigte meine Kollegin auf ihr Ohr, weil es seit gestern schmerzte.
At the doctor's office, my colleague pointed to her ear because it had been hurting since yesterday.