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Today I am going to talk about the internal structure of the crayfish. This is the second part of the article on crayfish anatomy (the first was about the external structure).
Basically, crayfish internal anatomy includes the following systems: the circulatory system, the respiratory system, the digestive system, the nervous system, and the reproductive system.
The majority of the internal organs are located in the Cephalothorax of the crayfish (the so-called head-chest area). The abdomen of crayfish is the main muscle that also contains the part of the intestine system.
Without further ado. Let’s look at each of these organs and systems in detail.
| Scientific name | Common name | Function |
|
Cephalothorax includes |
||
| Cerebral ganglion or ganglia or Encephalon | Brain | Contains a few nerve cell clusters. |
| Heart | Heart | Pumps blood to all organs of the crayfish |
| Pair maxillary and antennal glands | Green glands | Filtration and excretion. Remove metabolic waste and excess of water through the special pores. |
| Esophagus | Throat | Part of the digestive tract between the mouth and the stomach |
Two-chamber stomach
|
Stomach | Grinds food in the cardiac stomach and sorts it in the pyloric stomach.
The stomach is a part of the digestive tract between the esophagus and the intestine |
| Gastroliths | Calcium stones | Stores calcium for upcoming molt. |
| The gastric mill | Part of the stomach with teeth. | |
| Digestive gland | Liver | Secretes enzymes to break down the food and stores fats and glucose. |
| Cardiac muscle, and pyloric muscle | Anterior muscles Posterior muscles |
Stomach muscles |
| Mandible muscle | The mouthparts | They are involved in opening and closing the mandibles. |
|
Abdomen includes |
||
| Ventral nerve cord | Nervous system | The central nervous system of crayfish. It also activates the swimmeret system. |
| Extensor muscle | Abdomen muscles | Responsible for extending the abdomen or straightening it.
They are located on top of the abdomen. |
| Flexor muscle | Abdomen muscles | Bend the abdomen segments and curls the tail of the crayfish.
They are located along the sides of the abdomen. |
| Rectum and Anus | – | Excretes waste that cannot be digested. |
All crayfish species have an open circulatory system. It means that they almost do not have blood pressure and their entire abdominal cavity is filled with blood.
Note: Open circulatory systems function under low blood pressure and flow. It is almost ideal for simple animals with low metabolic rates. For example, very low blood pressure allows crayfish to live at great depths.
The diamond-shaped heart contracts to send the oxygenated blood into the spaces around the organs through several arteries. The heart is located at the posterior edge of the carapace.
The blood leaves the small arteries and flows around in the body cavity supplying internal organs with oxygen and nutrients. After that, when the heart relaxes, the blood passes through the gills and returns back into the heart through the two open-ended pores (ostia) in it to start the cycle again. These pores basically replace the capillary (veins) network in a crayfish body.
Crayfish have light blue blood. This is because they do not have hemoglobin. Their blood cells use hemocyanin, which gets its blue color from the copper that is part of its structure. To be precise, their so-called “Blood,” is a combination of haemocyanin and an interstitial fluid called “hemolymph”. Their blood can coagulate very rapidly.
Important: Hemolymph contains hemocyanin, which also contains two copper ions. Despite the fact that crayfish need a certain level of copper for proper blood circulation, like most invertebrates, they do not tolerate copper very well.
You can read more about “How Copper Affects Dwarf Shrimp” right here.
Crayfish do not have lungs, they use gills to gather oxygen and breath. The gills have a double set of leaf-shaped branches (in gill-chamber) and can be found on both sides of the carapace at the base of each walking leg (pereiopods). The gills can be identified as a fuzzy grey or brown organ.
Note: To be precise, the gills are located on the outside of the body cavity in a space between the body wall and the carapace. The carapace does not fit tightly against the body of the crayfish, there is a space between the body and the carapace so water can circulate through the gills.
Interesting fact: In crayfish, the gills also have a connection to the walking legs. So, as crayfish move the legs, the gills sweep through the water and that increases the contact between the water, and the gills and that increases gas exchange.
Unlike most aquatic creatures, crayfish have modified gills. They require water or high moisture to breathe. Therefore, as long as they are kept moist, the crayfish can stay on land for a long time without problems.
Crayfish are extremely opportunistic eaters. They are omnivores who are also scavengers. It means that their digestive system is very adaptable when it comes to feeding. It can break down both plants and animals as well as whatever else the crayfish can find.
The digestive system of crayfish can be divided into three main parts:
Interesting fact: Crayfish have teeth inside their stomachs for grinding food. This tooth-like structure is called the gastric mill.
The excretory system of crayfish consists of paired antennal glands (or the green glands), which rest in the basal antennal segment of the cephalothorax.
The green glands are positioned ventrally below the stomach and near the anterior end of the body cavity. These glands have spherical shapes.
Their main function is filtration and excretion. These are sort of like kidneys. The green glands remove metabolic waste and excess of water through the special pores. The openings for the green glands are located on the outer surface near the base of each antenna.
The nervous system of crayfish is multifunctional.
Functions:
Nonetheless, the nervous system of crayfish is also pretty simple compared to many other animals.
The brain is located on the back, or dorsal, side of the crayfish’s head (right behind and between the eyes). Actually, their brain can be called a brain only conditionally because it is very small and consists of only 3 nerve cell clusters (cerebral ganglion or ganglia).
These three fused nerve nodes are called:
The ventral nerve cord extends along the belly of the crayfish and runs to the rear end of the body (to the telson). It also has small nerve clusters at the end of each segment (walking legs, swimmerets, etc.).
Every segment is like semi-independent and provides motor nerve to the appendages. Basically, the nervous system of the crayfish is not completely centralized. It means that even if the cerebral ganglia is disabled, some parts of the crayfish would still move and react in a purposeful way while responding to external stimuli.
You can also read the article “Do Crabs, Crayfish or Shrimp Feel Pain?”.
In male crayfish, testes produce spermatids that are transported to and accumulate in the vas deferens. The testes (paired and soft organs) are located near and beneath the heart.
Each of them includes numerous tiny tubes, called seminiferous tubules. Each tubule has an inner lining of a single layer of epithelial cell which transforms into spermatozoa.
In addition, males have different pairs of swimmerets (copulatory pleopods) that are before the walking legs. These swimmerets are significantly longer than others. Males use them to transfer spermatids during mating.
In some crayfish species, they transfer spermatids from the special ducts at the base of the fourth walking limbs during mating.
In female crayfish, there are the paired ovaries, in which the eggs are produced. The matured eggs remain near the margin and the immature eggs occupy the center. Females have oviducts at the base of the second walking legs. It is from here that eggs will be shed.
Note: There is a crayfish species that can reproduce asexually or parthenogenetically (without males). This is a Marbled crayfish (Procambarus fallax virginalis or Procambarus virginalis sp. nov.).
When breeding is initiated, the male flips over and pins down the female and deposits spermatids near her seminal receptacle.
Insemination is external. It means that the union of reproductive cells occurs outside the body. The eggs travel down an oviduct and then they pass through a seminal receptacle where fertilization occurs.
After that female sticks the eggs on her pleopods. The brood pouch itself is formed by pleopods of the female. They hold the eggs until hatching day.
Introduction to the Crayfish Care – Setup, Diet, and Facts
How to Set Up a Crayfish Tank
Crayfish External Anatomy
Dwarf Shrimp External Anatomy
Dwarf Shrimp Internal Anatomy
Crab External Anatomy
Crab Internal Anatomy
