Virtual Dissection Lab

Arthropod

Background Info

Arthropods make up 90% of the animal kingdom and come in a variety of shapes and sizes.

Arthropods are described by an exoskeleton, a body divided into different regions, jointed appendages, and bilateral symmetry. All insects and crustaceans are arthropods but their are some small differences you will note in todays dissection so pay attention.

Objective

Today we will be dissecting and comparing to arthropods, the grasshopper and the crayfish. Lets begin with the grasshopper. On the external anatomy you can clearly see the segmentation, the eyes, the antennae, the wings, and the appendages. All insects have 3 pairs of legs. The grasshopper has highly modified hind legs. In the mouth their are mandibles that cause the physical breakdown of food. Now make an incision of the dorsal surface of the grasshopper from the thorax to the anus. Then pin back the exoskeleton. If you see large pronounced tubular structures then you have a females specimen and those are eggs. Remove the eggs if yours is female to view the other organs more clearly. On the region near the head their are some fibrous flaps. Those are muscle tissue. The digestive system consists of a mouth, then a pharynx, crop/food storage, finally the gizzard that performs mechanical breakdown. Above the gizzard are gastric ceca that produce enzymes to break down food. Then come the intestine, rectum and anus. You'll se a coil of fibrous tubes that are malpighian tubules. They act as kidneys.


Now we will move on to the crayfish. The crayfish is a freshwater crustacean. They have modified frontal appendages that are their claws. They are also segmented. Now take a look at its external features. The crayfish has 2 pairs of antennae, five pairs of limbs, a very hard exoskeleton. As crayfish grow they have to shed their exoskeleton. They only have two body regions, the cephalothorax and the abdomen. Crayfish have swimmerets for locomotion and water circulation. Females have modified swimmerets for egg care. While males have large hard swimmerets for sperm transfer. Remember that fertilization is external. Now we will begin opening up the crayfish. Now we will remove the dorsal exoskeleton and view the internal organs. Their are anterior and posterior gastric muscles. They are involved in digestion. The digestive system starts with the cardiac stomach and then the pyloric stomach. Their are some large digestive glands. Then the intestine ending at the anus. crayfish also have gastric teeth. On males the testis are small white pair of glands. The heart is near that. The heart has an open circulatory system. The antennal gland acts like a kidney.

Grasshopper Anatomy Part 1
Crayfish Anatomy Part 1

Arthropod Respiration

Aquatic arthropod poses gills for gas exchange in aquatic environments. This then connects to the circulatory system where its is carried through blood throughout the body. In terrestrial arthropods the trachea and book lungs take in oxygen and perform respiration for the bodies functions. In the grasshopper pores on the side of the abdomen ta in oxygen.

Taxonomy


Crayfish

Kingdom:Animalia

Phylum:Arthropoda

Subphylum:Crustacea

Class:Malacostraca

Order:Decapoda

Suborder:Pleocyemata

Infraorder:Astacidea




Grasshopper


Kingdom:Animalia

Phylum:Arthropoda

Subphylum:Hexapoda

Class:Insecta

Order:Orthoptera

Suborder:Caelifera

Evolution

Arthropods are segmented animals wit an exoskeleton, joined appendages, and body regions. Over time specialized appendages have developed in both the grasshopper and the crayfish. This is easy to see because of the crayfish's claw and the grasshopper's highly modified back legs. This is produced by generations of natural selection and environmental influences. The claws on a crayfish are for hunting and food gathering while the legs on a grasshopper are for locomotion.

Ecology

Grasshoppers are mostly herbivores that eat wild grasses and shrubs. They are considered pests by humans because they eat out grain crops. Grasshoppers are an important prey item to many animals, especially insectivores. They are commonly available and breed rapidly. Grasshoppers are found in most climates, but prefer grasslands.


Crayfish are freshwater crustaceans that are scavengers/carnivores. they use their modified front legs to tear pieces of food to eat. Crayfish play a key role in keeping water bodies clean from decay. they are also a delicacy from humans. The rising temperatures have messed up their mating habits inhibiting population grow while crayfish are continually being harvested. Through all this They are still able to survive.

Body Systems

Both animals have a respiratory, excretory, circulatory, digestive, and reproductive systems. Crayfish have gills and grasshoppers have book lungs and trachea for gas exchange. They both have a circulatory system with hearts and vein networks. The crayfish has an open circulatory system. The grasshopper has a crop and a gizzard while the crayfish has a stomach with internal teeth. The reproductive systems are similar with ovaries and testis, but the crayfish fertilization is external.

Human Impact

The use of insecticides and changing environments affect both of these animals in negative ways. Through crop dusting, because grasshoppers are consider pests, whole populations have died out. The only way they are able to survive is because of their amazing devotion to reproduction. The same can't be said for the crayfish as both changing climate and overfishing have destroyed their populations. Both are not currently endangered, but if this cycle continues the outcome could be unwanted.

Fun Facts

  • Crustacean shells are made of chitin
  • Arthropods are 90% of the animalia
  • All arthropods have segmented bodies
  • the majority of a female grasshopper's body is devoted to reproduction