Arthropoda—Crustacea
Melina Clinton
external image image.mason?imageID=6&size=600(click for larger image. 6) (SM)
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LJ (21)

Diagnostic Characteristics:

-All arthropods have jointed legs and a head and segmented body parts called the thorax and abdomen. An arthropod’s body is covered by a shell or a hard outer skin called an exoskeleton.(MP) 13
-Exoskeleton-The crustacean exoskeleton is made of the protein chitin, the same protein used in the cell walls of fungi, and calcium. This outer skeleton provides protection and rigid support for muscles. The exoskeleton is made of separate plates joined by thin membranes. This design resembles the design of medieval plate armor and allows for body movement. (KL)(1)

-Segmentation.

-Jointed appendages-Arthropod means 'jointed foot." These appendages were originally meant to be used for walking, and still are by many arthropods. However, in every arthropod group, appendages have evolved to serve other purposes: into antennas , mouthparts, claws, pinchers, gills, paddles, spines, stingers and spinnerets (web building). Appendages are often paired, and usually at least one paid can be found on each segment. (4) (CSR)

-Molting-is a hormonally controlled process that allows a crustacean to grow a second skeleton to adapt to its growing body. The tissue layer under the first skeleton detaches and creates a new skeleton, leaving the crustacean with 2 skeletons. Molting happens many times during the life of a crustacean because they are constantly growing. They leave their old skeleton behind and, for a brief period of time, are weak because their new skeleton cannot fully support their limbs just yet. (NG) (2)

-Open circulatory systems -> Hemolymph is propelled by the heart through short arteries into sinuses surrounding the tissues and organs. The Hemolymph reenters the heart through pores equipped with valves -> The main body cavity of Arthropoda—Crustacea is an open circulatory system, in which fluid (called hemolymph) in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients and there is no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph. Open circulatory system is where blood is pumped into the haemocoel by a heart located near the dorsum, the back or upper surface of a part of the body such as the hand or foot. The alimentary canal consists of a straight tube that often has a gizzard-like "gastric mill" for grinding food and a pair of digestive glands that absorb food; this structure goes in a spiral format. Structures that function as kidneys are located near the antennae. A brain exists in the form of ganglia close to the antennae, and a collection of major ganglia is found below the gut.(5)(ZS)
-Two pairs of antennae

-Aquatic- evolved in the ocean

Habitat:
-Live in almost every possible habitat, including fresh water, salt water, soil, and even in the most uninviting regions of Antarctica and high mountain regions. (DB) (22)

Development :
Crustaceans undergo larval stages before they fully develop into adults. The three larval stages include Naupli, Zoea, and Megalopea:
During the Naupli stage, the cephalic (head) segments arise along with the appendages that belong to those segments, which include mandibles, antennae, and antennules. An eye, referred to as a naupliar eye, develops in the middle of the anterior portion of their body. The organism also has a cephalic shield and can swim using its antennae. As the organism undergoes successive molts, it adds more segments and appendages leading to the Zoea and Megalopae stage. These types of larvae are only found in members of Malacostraca. The Zoea have compound eyes, thoracic (chest) segments and abdominal segments, which they use to swim. Megalopae (also known as post larvae) is the stage when the organisms will metamorphoses into their adult form. (MT) (8)


Acquiring/Digesting Food:

-Claws

-Eating bacteria and protists

-Most crustaceans are suspension filter-feeders. This means that they strain food particles from the water by passing them through specialized filtering structures. However, some of the larger crustacean species are able to be predators and scavengers. Also, the foreguts of some crustaceans are enlarged into both the cardiac and pyloric stomach. (7)(MF)

Sensing Environment:
-Antennae: Crustaceans have two sets of antennae. The first, smaller set, known as the antennules, extend from the mouth. These are uniramous, meaning they are not branching, and consist of a single series of segments attached end-to-end. The second larger set are biramous, or branching, meaning that they branch in two. Each branch is made up of a series of segments that are attached end-to-end. (ZXU)(3)
-Eyes: Crustaceans have two types of eyes frontal eyes and compound eyes. Frontal eyes tend to be simple eyes that are made up of only light sensory cells. Compound eyes on the other hand allow for a more complex sense of sight.(RL)(18,19)

Locomotion:

-Jointed, claw-like feet.

-Swim with jointed fin like appendages. Smaller crustaceans can swim in the water using their appendages, while the larger ones have to walk along the bottom of the body of water. (MLK) (17)
-Shrimps have many sets of legs. The first pair is used for feeding, but the next 5 pairs are used for walking. These have gills at their base. The rear legs are called swimmerets and are fringed with strong hairs or bristles. (SI) (20)


Respiration:

-Gills
-Paddle like appendages aid ventilation- increases the flow of respiratory medium- water

-Arrangement of capilaries aid gas exchange- blood flows opposite way of the water- counter current exchange- extremely efficient.


Metabolic Waste Removal:
-major nitrogen waste is excreted as uric acid
(YA)(4) The two major excretory organs among the crustaceans are the antennal gland and the maxillary gland. Both of these structures have an end sac and a convoluted duct that in some organisms expands deep into the bladder before reaching the opening to the outside. The primary function of these two glands is to regulate the ionic balance within the body. Ammonia, which is the end product of nitrogen metabolism needs a sufficient amount of water to “wash it away”, as it exits through the gills. But since terrestrial crustaceans do exist they have evolved to excrete ammonia as a gas, without being subject to toxic side-effects. As crustaceans age, only one of the two glands seem to fully function, and sometimes the operating gland may even change throughout its lifetime.

Circulation:
- Open circulatory systems -> Hemolymph is propelled by the heart through short arteries into sinuses surrounding the tissues and organs. The Hemolymph reenters the heart through pores equipped with valves
-Crustaceans have single-chambered Dorsal hearts. These hearts are made of three types of muscle: cardiac muscle, ostium muscle, and the muscles of the cardio-arterial valves. Valves in the arteries prevent the back-flow of blood, or hemolymph. Hemolymph is conducted to the gills for oxygen and carbon dioxide exchange. Hemolymph may be colorless, reddish, or bluish. The hemolymph contains ameboid cells that prevent clotting. (LW)(4)
-Hemocyanins (respiratory proteins that carry oxygen to the tissues) are present in the blood of particular crustaceans. (NI) 14
circulatory.jpg(CW)

Self Protection:
-Exoskeleton- cuticle like substance that covers the entire body- calcium carbonate
-Crustaceans are known for their hard shell and as a crustacean grows, its shell is removed and new one grows in. However, it takes time for the shell to harden and during this time the crustacean is vulnerable as it does not have its primary means of protection. Crustaceans do have claws to protect itself and some are able to produce a miniature sonic boom that can deafen predators. (AC)(15)
-Contrary to popular belief, crustaceans are able to feel pain- a major piece in self-preservation. Pain is an incredibly important process for the central nervous system in crustaceans- with it, they are able to be aware of potential bodily harm, and receive motivation to avoid a "painful" experience in the future. It was previously thought that crustaceans had no sense of pain as they had no brain structure similar to the neocortex- the part of the brain that processes pain and stress. However, crustaceans do have a suitable network of receptors and a proper central nervous system to have the important self-protective sense of pain. (TM)(9)
-Crustaceans usually have a carapace (a thick shield) that is made up of parts of the exoskeleton. The carapace covers the thorax and abdomen (trunk). (AK) (16)

Osmotic Balance:
-Composition of cytoplasm is the main controller
-The composition of cytoplasm is controlled by the hemolymph's composition
-For freshwater crustaceans, it it necessary to hold in salts and get rid of excess water. They do this by secreting a very diluted uring with low salt content through special "green glands".They replace any lost salt by taking in more water with their gills. Marine crustaceans actually have kidneys to get red of excess salt. (ORS 10)

Temperature Balance:
-Thermoconformers- little control over body heat
-Take temperature from environment

Questions:
1. How does the exoskeleton serve as protection for Crustacea? [MS]
2. How is blood circulated through the body of Crustacea? (RG)
3. Crustaceans have three larval stages. The first stage is when many appendages, the head, and other distinct anatomical features form. Name the other two stages and briefly describe how a crustacean gets from the primary larval stage, Naupli, to the later two stages? (SD)
4. How is the structure of the Crustacean digestive system related to its function?
5. What are the benefits of an open circulatory system? Would it work on a larger animal like a bear? Why or why not? (NG)

Sources:
1. http://www.oceaninn.com/the-nature-preserve/crustaceans/ (1,2)(KL)(NG)
2. www.hartnell.edu/faculty/nwheat/20.%20Crustaceans.ppt (LW) (4)
3. http://www.newworldencyclopedia.org/entry/Antenna_%28biology%29#Crustaceans (3)(ZXU)
4. http://icb.oxfordjournals.org/content/8/3/673.abstract (4)(YA)
http://jeb.biologists.org/cgi/content/full/212/11/1716 (4)(YA)
5. http://en.wikipedia.org/wiki/Crustacean (5)(ZS)
6. http://crustacea.nhm.org/glossary/image.mason?imageID=6&size=600(6)(SM)
7. http://zoology.muohio.edu/crist/Zoo312/Crustaceans.html(7)(MF)
8. http://www.ucmp.berkeley.edu/arthropoda/crustacea/metamorphosis.html (MT) (8)
9. http://blogs.discovermagazine.com/80beats/2009/03/27/the-misunderstood-crustacean-study-suggests-they-do-feel-pain/ (TM)(9)
10. http://biosciweb.net/animal/pdf/crus.pdf (ORS 10)
11. http://www.globio.org/glossopedia/article.aspx?art_id=15 (MP) 13
12. 14 http://www.daviddarling.info/encyclopedia/H/hemocyanin.html
13. http://www.seasky.org/reeflife/sea2e.html (AC)
14. http://www.animalfacts.net/crustaceans-lobsters-crabs-shrimp/index.html (AK)
15. http://www.sa.waterwatch.org.au/pdfs/critters_5_crustaceans.pdf (MLK)
16. http://zoology.muohio.edu/crist/Zoo312/Crustaceans.html (RL)
17. http://www.answers.com/topic/crustacea-2 (RL)
18. http://www.bumblebee.org/invertebrates/CRUSTACEA.htm
19. http://img.dailymail.co.uk/i/pix/2007/11_01/lobsterDM0811_468x521.jpg
20. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/I/Invertebrates.html