Crayfish: Characteristics, Anatomy & Habitat

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Crayfish, crawfish, craw-dads. No matter what you call them, in this lesson we're going to dissect them to find out what they are, where they live, and identify their major anatomical features.

What's in a Name?

Growing up in Michigan I was always playing in creeks, rivers, and lakes. There were plenty of critters to discover and learn about, including crayfish, which are fresh water crustaceans that look like mini lobsters. If you live in the southern United States, you may instead call them 'crawfish' or 'craw-dads', which I learned to do very quickly once I moved to that region of the country! Another fun fact, in Michigan, eating crayfish is not very common. But in the South, 'crawfish' boils are a delicious and fun summer staple.

Crawfish boils are common summer occurrences in the southern U.S.
crawfish boil

What and Where are Crayfish?

Crayfish are invertebrates which means they don't have a backbone. They are also arthropods, which means that they have a protective exoskeleton on the outside of their body. Other arthropods include insects, spiders, and centipedes. Crayfish continually shed their exoskeleton and regrow a new one. During this transition is when they are most vulnerable to predators because they aren't protected by their outer shell.

Crayfish are found all over the world in many different freshwater environments, such as rivers, creeks, springs, and swamps. But this doesn't necessarily mean that you will be able to find them. They are somewhat cryptic because they dig out homes for themselves under rocks and blend in well with their environment. Crayfish will ardently defend this dwelling against intruders using their strong front claws. I know from personal experience just how strong they are!

Crayfish are colored so that they blend in with their surroundings
image of a crayfish

Crayfish are nocturnal which means they sleep during the day and are active at night. Crayfish provide an important food source for many other aquatic animals (as well as land animals such as raccoons and opossums), though they themselves are omnivores, meaning they eat both plants and animals. Some favorite food items include insects, fish and frog eggs, and worms.

A female crayfish carries her eggs on the underside of her abdomen, and even after they hatch the babies will stay with her like that for several days before venturing out on a life of their own. The normal life span of a crayfish is about 2 - 3 years, and on average can get up to 6 inches in length though sometimes they are found to be larger.

Crayfish Anatomy

Crayfish have two body segments. The head may look like it is separate, but it's actually fused with the thorax forming the first segment, the cephalothorax. A hard protective carapace covers this first segment, protecting it like a shield. The back end of the crayfish is the abdomen.

On the head, we find the eyes, antennae, and antennules, which look like much shorter antennae. A crayfish will use its antennae for touch, taste, and smell, and its antennules for balance, touch, and taste. We also find the mouth parts of the crayfish here. The mandibles are the crushing jaws, and two pairs of maxillae hold and tear solid food before it reaches the mouth. There's yet another structure that helps with eating called the maxillipeds. These act like arms that hold food while the crayfish eats.

Crayfish use their large chelipeds for a variety of things, including defense
Crayfish chelipeds

Moving down the body, we come to the thorax. Internally, many of the crayfish's organs such as the heart, liver, and gills are found here. There are also external structures such as the walking legs, which are just what they sound like, as well as the chelipeds. These are those large front claw appendages that they use for picking things up, capturing prey, and defending themselves.

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