FootThe muscular wedge the clam moves with. It can reach out past the edge of the shell.
Incurrent siphonThe lower tube at the back. Water flows in through it, bringing food and oxygen.
Excurrent siphonThe upper tube at the back. Water leaves through it, carrying waste away.
GillsLeaf-like sheets that hang on each side of the body. They take oxygen from the water that flows over them.
MantleA soft sheet that lines each valve. It makes the shell.
Anterior adductor muscleThe muscle at the front that pulls the valves shut. It runs straight across from one valve to the other.
Posterior adductor muscleThe muscle at the back that pulls the valves shut. Together the two muscles hold the shell closed.
MouthA small opening just behind the front muscle. Two pairs of small flaps beside it, the palps, sweep food in.
StomachA wide part of the gut inside the digestive gland. The mouth opens into it by a short gullet.
Digestive glandA gland that surrounds the stomach, under the umbo. It makes digestive juice and is also called the liver.
IntestineA narrow tube that loops low in the body. It then runs back through the heart and over the rear muscle.
HeartThree chambers in a sac near the hinge. The end of the intestine runs straight through it.
KidneyIt lies under the heart, in front of the rear muscle. It takes waste out of the blood.
Inside the empty shell 7
UmboThe raised beak near the hinge, the oldest part of the valve. The shell has grown outward from it.
Hinge teethRidges just under the umbo. They lock with the teeth of the other valve and keep the two valves lined up.
Hinge ligamentA springy band that joins the two valves at the top. It pushes them apart when the muscles relax.
Anterior adductor muscle scarThe mark where the front adductor muscle was fixed to the valve.
Posterior adductor muscle scarThe mark where the rear adductor muscle was fixed to the valve.
Pallial lineA line near the lower edge that joins the two scars. It shows where the muscles of the mantle edge were fixed.
Pallial sinusA notch in the pallial line, near the rear scar. It marks where the siphons pull back into the shell.
How this list was compiled: Every name checked on 2026-10-01 in two sources. H. S. Pratt, A Course in Invertebrate Zoology (1902, public domain), the hard-shell clam: the shell and its marks, the mantle, siphons, gills, foot and muscles, and the organs seen through the body wall, https://archive.org/details/courseininverteb00prat. Wikipedia, Bivalvia, Bivalve shell, Hard clam, Hinge teeth, Pallial line and Pallial sinus, https://en.wikipedia.org/wiki/Bivalvia. R. W. Hegner, College Zoology (1912, public domain), the anatomy of a bivalve: mouth, stomach, digestive gland, intestine, heart and kidney, https://archive.org/details/collegezoology00hegn. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
A clam labeled diagram left blank: a hard-shell clam in one half of its shell, and below it the inside of the empty shell. Thirteen lines lead from the body and seven from the shell, each ending in blank space.
Read the full guide
Thirteen names on the body
Along the top, from the left: digestive gland, stomach, heart, kidney, intestine. Down the left side: mouth, then anterior adductor muscle. Down the right: posterior adductor muscle, then excurrent siphon. Along the bottom: foot, mantle, gills, incurrent siphon.
Seven names inside the empty shell
At the top, the left line ends on the peak, the umbo, and the right one on the band behind it, the hinge ligament. Down the left: hinge teeth, then anterior adductor muscle scar. On the right: posterior adductor muscle scar. Underneath, the left line ends on the pallial line and the right one in the pocket it makes, the pallial sinus.
The front of the clam is at the left in both drawings: every anterior name goes on the left, every posterior name on the right.
Drawn with no line: the two small flaps by the mouth, called palps, the tube from mouth to stomach, and the arrows at the siphons.
A class sheet may print inhalant and exhalant, or branchial and cloacal, for the incurrent and excurrent siphons.
Questions and answers
How do you tell the front of a clam shell from the back?
Three marks on the empty shell help. The umbo most often leans toward the front, the hinge ligament usually lies behind the umbo, and the pallial sinus points to the rear, where the siphons are.
How many gills does a clam have?
Four: two on each side of the body, though the sheet draws only one. The two gills of a side count as a single organ, a ctenidium, so a clam has one pair of ctenidia.
Does a clam have a head?
No. Bivalves have no head, and they lack the radula, the toothed ribbon that most other mollusks feed with. The sheet has a line to the mouth and none to a head, an eye or a tentacle.
Is a quahog a hard-shell clam?
Yes. The hard clam is also called the round clam, the hard-shell clam and the quahog. It is native to the eastern shores of North and Central America, and older books list it as Venus mercenaria.
Does the anatomy of a clam no labels sheet have an answer key?
Yes. The key is the same sheet with a name at the end of each of the twenty lines. Four are written short: Ant. adductor, Post. adductor, Ant. scar and Post. scar.