Mussel Diagram Unlabeled – Shell Outside and Body Inside

All 14 parts on the diagram

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The shell, outside 5

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.
Umbo The oldest part of the valve, at its pointed front tip. The shell has grown outward from here.
Growth lines Ridges that follow the edge of the shell. They mark the pauses between one period of growth and the next.
Hinge ligament A springy band that joins the two valves along the top edge. When the muscles relax, it opens the valves again.
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

Mantle Two flaps of the body wall, one lining each valve. The mantle makes the shell.
Visceral mass The soft body in the middle. It holds the stomach, the digestive gland and the other main organs.
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.
Anterior adductor muscle The small muscle at the front. It also pulls the valves together, but in a sea mussel it is much reduced.
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.
Foot Small and tongue-shaped in a sea mussel. A groove along it leads from the pit where the byssal threads are made.
Labial palps Small flaps beside the mouth. They pass the food caught by the gills into the mouth.
Incurrent siphon The opening where water is drawn in. The water brings oxygen and food.
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

This mussel diagram is unlabeled: the closed shell on its rock above, and below it the same mussel with the near valve taken off. Fourteen parts wait for a name, and eleven of them have a line.

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The word list

Five names go on the shell: valve, umbo, growth lines, hinge ligament and byssal threads. Nine go on the opened mussel: mantle, visceral mass, gills, foot, labial palps, anterior adductor muscle, posterior adductor muscle, incurrent siphon and excurrent siphon.

Three parts with no line

The valve, the visceral mass and the gills are large enough to write on. The valve is the whole face of the shell. The visceral mass is the plain lump in the upper middle of the opened mussel, and the gills are the long striped band under it.

The pointed end is the front. The small muscle beside it is the anterior adductor; the large round one near the siphons is the posterior.
The threads are drawn twice, under the shell and at the base of the foot. Only the upper set has a line.
A textbook may print byssus for the threads, and inhalant and exhalant for the two siphons.

Questions and answers

What are the parts of a mussel to label?

Fourteen on this sheet: five on the shell, from the valve to the byssal threads, and nine inside, from the mantle to the two siphons. The rock and the two arrows are drawn but take no name.

How do you tell the incurrent siphon from the excurrent siphon?

By the arrows at the rear edge. Water goes in at the incurrent siphon, the lower opening with a fringe, where the arrow points into the shell. The arrow that points away marks the excurrent siphon above it.

Where is the foot on a mussel diagram?

At the front of the striped gills: the narrow tongue that hangs down, with threads leaving at its base. The small three-cornered flaps just ahead of it are the labial palps, which have a line of their own.

Where is the mantle on a mussel diagram?

It is the wide sheet that lines the shell and fills it almost to the edge. Its line ends under the gills. The rim outside it is the far valve, which is still in place.