• 14 parts
  • Checked September 2026

Parts of a Mussel

A sea mussel from outside, then with one half of its shell taken off.

Parts of a Mussel

Name Date

Tap any part to read, rename or leave it out

1 2 3 4 5 6 7 8 9 10 11 12 13 14
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Write the name of each numbered part.Answer key

  1. Valve
  2. Umbo
  3. Growth lines
  4. Hinge ligament
  5. Byssal threads
  6. Mantle
  7. Visceral mass
  8. Posterior adductor muscle
  9. Anterior adductor muscle
  10. Gills
  11. Foot
  12. Labial palps
  13. Incurrent siphon
  14. Excurrent siphon

Drawn for this site on 2026-09-30 from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: a squid, another mollusk

All 14 parts on the diagram

Show the list

The shell, outside 5

  1. Valve One of the two hinged halves of the shell. The shell supports the soft body and protects it from predators and from drying out.
  2. Umbo The oldest part of the valve, at its pointed front tip. The shell has grown outward from here.
  3. Growth lines Ridges that follow the edge of the shell. They mark the pauses between one period of growth and the next.
  4. Hinge ligament A springy band that joins the two valves along the top edge. When the muscles relax, it opens the valves again.
  5. Byssal threads Tough, stretchy threads that fix the mussel to a rock. The foot lays them down as a liquid that hardens in sea water. Cooks call them the beard.

Inside the shell 9

  1. Mantle Two flaps of the body wall, one lining each valve. The mantle makes the shell.
  2. Visceral mass The soft body in the middle. It holds the stomach, the digestive gland and the other main organs.
  3. Posterior adductor muscle The large muscle at the rear that pulls the two valves shut. In a sea mussel it does most of the work.
  4. Anterior adductor muscle The small muscle at the front. It also pulls the valves together, but in a sea mussel it is much reduced.
  5. Gills Long sheets on each side of the body. They take oxygen from the water, and their cilia move the water along and catch the food in it.
  6. Foot Small and tongue-shaped in a sea mussel. A groove along it leads from the pit where the byssal threads are made.
  7. Labial palps Small flaps beside the mouth. They pass the food caught by the gills into the mouth.
  8. Incurrent siphon The opening where water is drawn in. The water brings oxygen and food.
  9. Excurrent siphon The smaller opening where the used water and the wastes leave.

How this list was compiled: Every name checked on 2026-09-30 in two sources. Wikipedia, Mussel, Byssus, Bivalve shell and Bivalvia: the valves, ligament, adductor muscles, mantle, foot, byssal threads, gills, labial palps and siphons, https://en.wikipedia.org/wiki/Mussel. R. W. Hegner, College Zoology (1912, public domain), the fresh-water mussel: umbo, lines of growth, hinge, mantle, gills, foot, visceral mass, palps and siphons, https://archive.org/details/collegezoology00hegn. T. J. Parker and W. A. Haswell, A Text-book of Zoology, volume 1 (1910, public domain), for the sea-mussel's byssus and its unequal adductor muscles, https://archive.org/details/textbookofzoolog00park. Also H. S. Pratt, A Course in Invertebrate Zoology (1902), and Animal Diversity Web, Bivalvia, https://animaldiversity.org/accounts/Bivalvia/. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Licence: own work

How it works

The parts of a mussel, drawn on a sea mussel of the kind that is cooked and eaten. The first view shows the shell on its rock. The second takes one valve off to show the body inside. It is a plan, not to scale.

Read the full guide

Outside

The pointed end is the front. Its tip is the umbo, the oldest part of the shell, and the growth lines spread out from it. The hinge ligament runs along the top edge. The byssal threads, the beard, hold the mussel to its rock.

Inside

Switch to Inside. The mantle lines the shell, and the striped gills hang below the soft visceral mass. Two adductor muscles close the shell, a small one in front and a large one behind. Water enters by the lower siphon and leaves by the upper. Press Quiz me to name each part yourself.

  • Beard and byssus are the same thing: the threads that anchor the mussel.

Questions and answers

What is the beard on a mussel?

The byssus: a bundle of tough threads the mussel makes to fix itself to rocks. It is not eaten, and it is pulled off when mussels are cleaned or cooked.

How does a mussel eat?

It is a filter feeder. It draws water in through the incurrent siphon, and the gills catch the plankton in it. The labial palps pass the food to the mouth, and the water leaves by the excurrent siphon.

How does a mussel open and close its shell?

The adductor muscles pull the two valves shut. When they relax, the springy hinge ligament pushes the valves apart again.

Do mussels have a foot?

Yes. In a sea mussel it is small and tongue-shaped, and it lays the byssal threads. Freshwater mussels have a large foot and use it to pull themselves through sand or mud.

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