Crayfish Internal Anatomy Quiz – Organs From the Side

All 17 organs on the diagram

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Food path (7) 7

Stomach A large sac in two chambers. The front chamber is the bigger one.
Intestine A straight tube from the stomach to the anus.
Digestive gland It makes the juice that breaks food down. Older books call it the liver.
Mouth Food goes in here, between the jaws.
Esophagus A short, wide tube from the mouth up to the stomach.
Anus The opening under the tail where waste leaves.
Gastric mill Hard teeth inside the stomach. They grind the food small.

Blood and breathing (5) 5

Heart It lies under the back and pumps blood into the arteries. Blood enters it through small openings with valves.
Gills Feathery organs that take oxygen from the water.
Dorsal abdominal artery It carries blood from the heart back through the abdomen.
Sternal artery It runs straight down from the heart to the body floor.
Ophthalmic artery It carries blood from the heart forward to the head.

Nerves, gland and muscles (5) 5

Green gland It takes waste out of the blood. Its duct opens at the base of the antenna.
Brain A mass of nerve tissue in the head. It sends nerves to the eyes and feelers.
Ventral nerve cord A chain of nerve centers along the floor of the body.
Flexor muscles They bend the abdomen, which shoots the crayfish backward.
Extensor muscles They straighten the abdomen again.

How this list was compiled: Every name checked on 2026-10-01 in two public-domain texts read on archive.org. (1) R. W. Hegner, College Zoology (1912): the crayfish, internal organs, https://archive.org/details/collegezoology00hegn. (2) T. H. Huxley, The Crayfish: An Introduction to the Study of Zoology (1880), https://archive.org/details/crayfishintroduc00huxl_2. Where the two differ in wording the newer name is the label and the older one is accepted: digestive gland (Huxley: liver), dorsal abdominal artery (Huxley: superior abdominal artery), ventral nerve cord (Huxley: chain of ganglia), esophagus (Huxley: gullet), anus (Huxley: vent). Licence: own work

The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work

How it works

This crayfish internal anatomy quiz shows the animal from its left side with the body wall drawn away. A ring marks one organ; pick its name from four. The labeled drawing is one press away.

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Where the organs lie

The stomach fills much of the head, with the teeth of the gastric mill inside it. The digestive gland lies below it and the intestine runs back to the anus under the tail. The heart sits under the back of the thorax and sends arteries forward, backward and down. The gills are low at the sides.

Head, floor and tail

The brain is in the head near the eye, and the green gland is below it. The ventral nerve cord runs along the floor of the body. In the abdomen a thin band of extensor muscles lies above the intestine and a thick block of flexor muscles below it.

The body is drawn deeper than it is, so each organ has room. Positions are right; proportions are not.

Questions and answers

What organs are inside a crayfish?

A stomach with a gastric mill, a digestive gland and an intestine; a heart, arteries and gills; a brain and a ventral nerve cord; a pair of green glands; and the flexor and extensor muscles of the abdomen.

What is the gastric mill of a crayfish?

A set of hard teeth inside the front chamber of the stomach. They grind the food into fine pieces before it passes into the second chamber.

Where is the heart of a crayfish?

Under the back of the thorax, behind the stomach. Blood enters it through small openings with valves and is pumped out through arteries that run forward, backward and down.

What does the green gland do in a crayfish?

It takes waste out of the blood. A crayfish has a pair of green glands low in the head, and each one opens at the base of an antenna.