AY Honors/Crustaceans/Answer Key

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1. Name at least four characteristics of a crustacean.

Like all Arthropods, Crustaceans have an exoskeleton, a segmented body, and jointed limbs. Most crustaceans have biramous limbs (limbs that branch into two, rather than uniramous, or in a single series of segments), breath through gills, have two pair of antennae, have eyes on stalks, seven or more pairs of limbs, and mouths made up of one pair of mandibles and two pair of maxillae.

2. What is an exoskeleton?

An exoskeleton is the hard outside covering in crustaceans (and many other animals, including all of the arthropods). In crustaceans, the exoskeleton is made of the protein chitin, reinforced with calcium. Crustacean exoskeletons do not grow with the animal, thus as the animal grows, it must periodically shed (or molt) its exoskeleton. The crustacean is frequently vulnerable following the molt until its new exoskeleton hardens.

If you have ever seen "soft-shell crabs" listed at a restaurant or in a grocery store or fish market, these are crabs who have just molted, but their new exoskeletons have not yet hardened.

3. What phylum does this group belong to?

Crustaceans are classified in the Kingdom Animalia, Phylum Arthropoda, Subphylum Crustacea.

4. How are the body of these animals divided?

Like all Arthropods, Crustacean bodies are made of three main divisions - the Head, Thorax and Abdomen. In many crustaceans, the head and thorax are fused into a cephalothorax. Each body division can be composed of several segments, each segment often having its own pair of appendages. The abdomen in crustaceans such as shrimp and lobsters is hinged in many segments, allowing them greater flexibility. In crabs, the abdomen is often folded under the animal, making them appear tail-less.

5. In which Bible passages can information be found about consuming crustaceans?

Discussions on eating crustaceans can be found in Mosaic food regulations in Leviticus 11:9-12 and Deuteronomy 14:9-10. God forbids eating them.

6. How are a siri and a crab different? Where can these animals be found?

Siri is another word for swimming crabs, in the genus Callinectes. The legs of walking crabs are referred to as pereopods, the modified appendages of swimming crabs as pleopods. The pleopods are flattened and oar-like, allowing the crabs to move through the water. Swimming crabs are found in many marine environments around the world, often in near shore areas with sandy bottoms. Walking crabs are found in both sandy and rocky areas offshore and onshore.

Common swimming crabs (siri) on the U.S. coast include the Blue Crab.

7. Name a land crab.

Ghost Crabs (Ocypode sp.) and Blue Land Crabs (Cardisoma guanhumi) are common land crabs along the U.S. south and east coasts.

8. How can you tell the difference between a male and female siri? Why is it important?

The tail flap that folds under the abdomen is much wider in female swimming crabs than in male swimming crabs. This wider flap is used for carrying eggs in the female.

9. What is the importance of small crustaceans for the environment?

Small crustaceans serve several important roles. They are often the first level of consumers in trophic webs, eating algae and phytoplankton, or serving as scavengers eating detritus and other decaying and waste material. As such, they are a critical component in keeping marine environments clean. But small crustaceans are also a very important component of the food webs as a source of nourishment for progressively larger animals, and crustaceans are among the most abundant organisms in numbers and weight in marine environments.

Perhaps the most striking relationship is between the Blue Whale and the crustacean Krill, one of its primary food sources. Blue whales can eat between two and four tons of krill a day, and by some accounts can, in particularly rich waters, gulp an astonishing thousand pounds of krill in a single mouthful.