Meru Nangia
edited by:
Yasheka Sharma
Sarah Schwarzschild
Hilary Stepansky
Rachel Kornetsky
Ethan Richman
Becca Levenson
Josh Czik
Brittany Marcus-Blank
Vonai Moyo
Arielle Reiter
Grace Rehnquist
Jesse Carmen
Kevin Nayer
Sarah Vlach
A Decapod Crustacean (
A Decapod Crustacean (


Phylum: Arthropoda

Subphylum: Crustacea

Crustacea is considered to be one of the major subphylums under the general phylum of Arthropoda. It encompasses various major classes, some of which are discussed below. This subphylum includes animals such as lobster, crab, crayfish, shrimp, and barnacles. Crustaceans tend to be marine animals, however some exceptions include wood lice and pill bugs - land animals that tend to be live in moist environments.

Table of Contents

Characteristics of Arthropods
Characteristics of Crustacea
Sessile crustaceans

Characteristics - Arthropoda
Crustacea are a type of arthropoda, and it is necessary to understand the characteristics of arthropoda to understand crustaceans. Arthropoda is one of the most diverse and distributed of all phylum. Almost one million different arthropod species have been described by scientists, and it is believed that up to a billion billion different species of arthropods exists in the world.
Arthropods are characterized by three traits: an exoskeleton that molts, jointed appendages, and a distinctly segmented body. Arthropod actually means "jointed feet", referring to the jointed appendages and the segmented body. The segmented body of an arthropod allows for efficiency in the organism. The different segments and their respective appendages have the ability to specialize and create a division of labor. The different segments may specialize for sensing, walking, eating, defense, etc.
Arthropods are are covered by an exoskeleton, or a cuticle, which is an external shell that surrounds their body. It is formed from layers of protein and chitin. The cuticle various across the breadth of the organism. In certain areas it can be very hard and dense, serving as a shell used for protecting the organism. In other areas, such as over joints, the cuticle is paperthin and flexible. The exoskeleton also provides a surface over which the muscle can attach. The exoskeleton is also relatively impermeable to water, which is what allows crustaceans to live in the water and still be able to regulate their body and control osmosis. There is one drawback to athropods having an exoskeleton. That is, as the organism grows, the exoskeleton becomes too small and the organism must shed the old one and secrete a new one. This process, known as molting or ecdysis, requires a lot of energy and also leaves the organism unprotected for a period of time.
As the organism's exoskeleton detatches, it secretes a new one. This leaves the crustacean with two skeletons. After the skeleton is complete, the outer skeleton splits along weak points, and the crustacean and the new skeleton emerge from the intact old skeleton. (12)(RJS)

This pillbug has just molted (the old exoskeleton is on the left and the pillbug is on the right). (DP)
This pillbug has just molted (the old exoskeleton is on the left and the pillbug is on the right). (DP)

Characteristics - Crustacea

Diagnostic Characteristics - Crustaceans are diagnosed by the extent of the specialization of their appendages. Crustaceans are the only athropods that have specialized their appendages so that they have two pairs of antennae. Crustaceans also have three or more pair of appendages that have specialized into mouthpieces, which includes the hard mandibles. The walking legs of crustaceans are attached to the thorax (refer to diagram above) and crustaceans also have appendages attached to their abdomen. Crustaceans also have the ability to regenerate lost appendages.

Appendages(Locomotion and Sensing the environment) - Crustacea use their specialized appendages to move and sense their environment. They have well developed sensory organs, including eyes, olfactory receptors for smell, and antennae for touch and small. Their appendages are also specialized so that they have the ability to both swim in water and walk upon a surface.

 chamber of a decapod crustacean
chamber of a decapod crustacean
Respiration - There are two types of respiration used by crustaceans. Small crustaceans exchange gases across areas of their cuticle that are thin. Larger crustaceans have gills through which they perform respiration. Gills can only function if they are kept moist. Water enters the crustacean at the base of a cheliped, claw, where it flows into the special gill chamber that holds water. Filaments dangle in the water within the chamber and they extract oxygen from the air within the chamber. The picture above displays the cycle of water through a crustacean. (8) (BMB)

Reproduction - The two sexes tend to be separate within crustaceans. Crustecean sex type is determined by swimmerets(also called peleopods), which are abdominal appendages (4 SES). Male crustaceans have larger first (and sometimes second) pairs of swimmerets than females do (4 SES). Swimmerets are illustrated below.Terrestrial crabs, which mate seasonally on land, must come back to the sea to release the eggs (4 SES). The females tend to hold onto the eggs until they hatch into independent larvae (4 SES). The methods of reproduction within crustaceans varies, however. A specialized case is that of lobsters and crayfish, in which the male uses a special appendage to transfer sperm into the female. All crustacean go through at least one larval stage, if not more.

external image lobster-1.gif
Here the arrows are pointing to swimmerets of a male lobster. (11 DJ)

Circulation - Crustaceans have an open circulatory system, where fluid bathes organs directly with oxygen and nutrients and there is no distinction between blood and interstitial fluid (6)(ER). A heart pumps hemolymph, rich fluid (ER), through arteries into sinuses (hemocoel) that cover the various organs, transferring the oxygen to the organ's cells.

Acquiring and ingesting food - Crustacea are mainly carnivores or scavengers. Also herbivores and detritivores are also common but not as common as carnivores. Although rare, in high density populations where there are a lot of animals and not enough food to go around, cannibalism can occur. Food is acquired by injesting through the mouth. Digestions begins after the food is past the gastric mill (a tube with sharp spines), where it is made into smaller pieces. In the midgut the food is fully digested and then it is passed out by the hindgut. (HS 5)

Metabolic waste removal/Osmotic balance - Crustaceans dispose of their nitrogenous waste by excreting through thin areas of their cuticles. They also have a pair of glands that regulate the salt balance of the hemolymph.

Self protection - Some crustaceans have specialized appendages used for defense such as claws or pincers. other crustaceans have hardened shells of calcium carbonate which helps to protect them. All crustaceans have an exoskeleton on the outside of their body which also serves as a form of protection.

Temperature balance - Crustaceans are ectotherms, which means that they have a metabolic rate that is too low to generate enough heat to effect body temperature. Their body temperature is detemined by their surrounding environment. Crustaceans are also thermoconformers which means that their body temperature changes with the changing temperature of their surroundings. Ectotherms can regulate their body temperature sometimes by behavioral mechanisms. For example, in the crustaceans' case the crustacean could move to shallower waters where it is warmer to raise its body temperature. (1 RK)

Limitations of Crustaceans- Crustaceans are not very successful on land. They lack a "waxy, water-tight" cuticle, unlike other insects that include a wax layer cuticle which helps them occupy land successfully. Also, the gills crustaceans have for respiration function best in water, and only some species have been able to use them on land.
(3. Sharma)

Isopods -
Deep Sea Giant Isopod (
Deep Sea Giant Isopod (

Isopod is an organism that has equal number of feet and similar legs on both sides. Isopods make up one one of the more numerous groups of crustaceans, and consist mostly of small marine species, all though some can become quite large, such as the one shown above. Isopods get oxygen through the gill-like structures located at the basses of their legs, rather than the lungs. This is why they must keep moist at all times, or else they die. Isopods also include the few land dwelling crustaceans, including wood lice and pillbugs. (2. Sharma) Isopod feeding habits are extremely diverse(9 VM). Within specific habitats, the isopods usually make up a major component of the energy cycle, and act as micrograzers, micropredators, parasites, and detritivores(9 VM). The primitive suborders are generally herbivores or herbivorous scavengers, and can significantly impact vegetation(9 VM). The more derived suborders are carnivores, predators, and parasites (9 VM).

Copepods -
A Copepod (
A Copepod (

Copepods are the most populous of all animals. They tend to be small crustaceans that make up most of the marine and freshwater plankton communities. They eat protists and bacteia and are consumed by a multitude of fish (1). Some species of Copepods are parasitic, meaning they suck the tissues of their host animals, in or on which they live. Although most species of Copepods reproduce sexually, some reproduce by parthenogenesis, which means the eggs do not need to be fertilized by a male sperm before it can develop into a new organism (7 BL)

Decapods -
The armed nylon shrimp (Heterocarpus ensifer), a deep-water decapod. (
The armed nylon shrimp (Heterocarpus ensifer), a deep-water decapod. (

Decapods are the most well known of all crustacea. This class consists of species such as lobster, crayfish, crab, and shrimp. They are called decapods because they have ten segmentations in their bodies. The three front parts are usually mouthparts and are called maxillipeds (10, AR). Decapods also have appendedages coming off of the sides of their body which are used for walking and food retrieval. If the decapod has a pair of enlarged, pincer like claws they are referred to as chelipeds, such as lobsters or crab (8, GR). The exoskeleton of decapods is hardened calcium carbonate and part of the exoskeleton forms a shield called the carapace. The large majority of decapods tend to be marine animals, however, there are some freshwater crayfish and some crabs species that live on land. It is under debate whether decapods should be divided into two suborders; natantia (swimming decapods) and reptantia (walking decapods). (10, AR). There is also debate whether suborders should arise for larvae developmentof gills and legs. These suborders would be dendrobranchiata and pleocyemata. (10, AR).

Sessile crustaceans -
Northern Rock Barnacle, Balanus balanoides (
Northern Rock Barnacle, Balanus balanoides (

Sessile crustaceans are specialized barnacles that have parts of thier cuticles hardened into shells by calcium carbonate. Barnacles are the least mobile of all crustaceans; they tend to adhere to rocks or other organisms. Sessile crustaceans strain food and nutrients from the water through their appendages. Adult barnacles lose their eyes and second antenna, and they stand on their head. Their appendages face out and act as a filter for when they feed. They kick their six legs to bring food to their mouth. (JAC) [7] A great example of filter feeding is shown in the picture below as a barnacle extends its legs to filter feed.(11)(SJB)
An example of filter feeding
An example of filter feeding

Review Questions
1) How do the respiratory methods used by crustaceans allow them to live in an aquatic (water) environment? [HZ]
2) What is the scientific terms for crustacea which are walking decapods? [OZ]

3) Explain for what and how crustaceans use their appendages. {Jesse Carmen}
4) What are the features that distinguish the different types of Crustaceans? (KN)
5) What is the overarching type of self defense/protection for all crustaceans? (SV)
6) How do Crustaceans maintaina temperature balance? (NK)
7) Given their unique capabilities, how has each type of crustacean adapted to its environment? (SS)

1. Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston: Benjamin-Cummings Company, 2002.

2. Isopods. Lawrence Hall of Science. University of California. 30 Nov. 2008.<
3. Crustacea. 19 Nov. 2008. <>
4. "Reproduction." Crustacean. 2 Dec. 2008. <>
(5) Hebert, Paul D. "Crustacea." The encylopedia of earth. 26 Nov. 2008. 2 Dec. 2008 <>.
6. Farabee, M.J. "The Circulatory System."
7. "copepod." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 07 Dec. 2008 <>.
[7] "Barnacle." The Canadian Encyclopedia. 2008. The Canadian Encyclopedia. 7 Dec. 2008 <>.
(8) Davey, Keith. "Oxygen and Respiration." Biological Factors. 2000. MESA. 7 Dec. 2008 <>.
(9) Brusca, Richard. "Isopoda." 7 Dec 2008
(10) "Encyclopedia> Decopods." NationMasterEncyclopedia. 7 Dec 2008. <>

(11)Piparo, John. "How do you tell a Male Lobster from a Female?" Monstah Lobstah. 17 Dec. 2008
(12)"Molting." 18 Dec 2008 <>.