Biology 110ANIMAL LABPhylum ArthropodaCrayfishPhylum EchinodermStarfish Phylum ChordataFrog Spring 2006Phylum ArthropodaArthropods are considered to be the most successful group of animals to ever to live because of their diversity, distribution, and sheer numbers. Zoologists have identified over one million species and estimate there are between 2 to 30 million yet to be discovered. Arthropod’s success is attributed to 2 physical factors: jointed appendages and an exoskeleton or cuticle. To grow they must molt i.e. shed their old cuticle and secrete a new one. This Phylum is divided into five major classes: arachnids (spiders), insects, millipedes, centipedes, and crustaceans (crayfish).EXTERNAL ANATOMYThe outer covering is a hard shell made of layers of chitin and protein called the exoskeleton or cuticle. Layering permits the cuticle to be thick and armor like for protection or thin and flexible for easy joint movement. This covering additionally provides support and slows water loss.The segmented body is divided into 2 areas: cephalothorax and abdominal. Each body area has pairs of jointed appendages modified for special functions. There are antennaeand antennules, both possessing numerous sensory receptacles, e.g. smell, movement. Attached to the ventral side (belly) of the cephalothorax are five pairs of walking legs. The first and largest pair, chelipeds, is used in defense and attacking. The second pair assists in walking as well as moving food to the mandibles which are modified mouth parts used to grind food and stuff it into the mouth opening. The mandibles are located just forward of where the chelipeds attach to the body. You must move the feeding appendages, maxillipeds, to see them.Jointed appendages also include the five pairs of swimmerets found on the underside of the abdomen. In females (see below) they are long and flexible, additionally serving as attach points for fertile eggs. In males, the first 2 pairs (the ones nearest the cephalothorax) are long, somewhat ‘L’ shaped, and somewhat inflexible. These are the male’s claspers (5) and they function as sperm transporters. The last 3 pairs of swimmerets on the male are typically short. Be able to identify males from females!!!The exterior also includes a central tail fin, the telson and two fins to either side of this fin, the uropods. The area between the eyes is the rostrum. The carapace is that portion of the cephalothorax exoskeleton behind the rostrum.INTERNAL ANATOMY How to get inside:On the dorsal (back) side of the crayfish insert the tip of the scissors between the abdomen and the cephalothorax so that the blades are cutting towards the rostrum. Cut until ¼” behind the eyes.Then cut left and right behind the eyes through the side exoskeleton.Now you can remove the carapace from the underlying organs by carefully using a blunt probe to separate the exoskeleton from the fascia attaching it to the internal body parts.BE CAREFUL WHEN YOU EXAMINE THE INSIDES. GO SLOW ANDJUST DON’T SHOVE THINGS AROUND. IT ALL LOOKS THE SAMEAT FIRST.Face the crayfish away from you, so that you are going from tail to head. As you move from the abdomen into the cephalothorax, both sides are covered with feathery gills. Brush them back.The top of the exposed area might still be covered with a membrane. If so remove it. Centered about ½” from the abdomen you should see a small diamond shaped organ; this is the heart. It is small about ¼” by 1/8”, has an ‘empty’ color and if you cannot immediately find it, ask the instructor for help before pushing things around. It is easily lost, destroyed. Tan or yellow heptopancreatic tissue fills up a goodly portion of the internal cavity. It aids in digestion. Forward of this tissue is a large sac membrane, the stomach. It is somewhat dark in appearance and may have split/been cut open to reveal a black mass, itslast meal. Using blunt nosed tweezers, remove the stomach, cut it open, wash out its contents, and feel/see the gastric mill inside. These are black structures that function as teeth and look like teeth. See the demo on the counter.If the following are not readily seen, you must ‘clean up’ the area/remove the bottom portion of the stomach. Be delicate. At the bottom of the space where the stomach once was, you should see two thread-like structures, the ventral nerve chords. On either side of these chords, there are oval structures called green glands. These glands aid in