Amazing Arthropods

ASHLEY MOODY VU-PAPBIO-3 4/9/14

Crayfish

Crayfish live in freshwater ecosystems, such as streams, rivers, and lakes. They are crustaceans that look like the smaller version of a lobster. Its eyes allow it to have a broad range of vision because of their location. Crayfish are mostly nocturnal, meaning they feed eat and travel at night. They are located at the bottom of bodies of water among the rocks, so they eat mostly dead insects, worm, fish, and algae. The crayfish uses its strong tail to quickly escape from predators, who include fish, birds, alligators, and humans.

Grasshoppers

Located on every continent except Antarctica, there are over 11,000 species of grasshoppers. The females are bigger than males and have pointed abdomens to help them lay eggs, but both genders have two pairs of wings, two antennae, two hind legs, mandibles, and exceptional jumping skills. Most are camouflaged to match their surroundings. Grasshoppers are mainly herbivores, eating plants and vegetables, but will eat dead insects. A few have been known to eat toxic plants and then store the toxins for future use against predators, who include birds, reptiles, rodents, spiders, beetles, other insects, and even humans. Chocolate-covered grasshoppers are a delicacy in some parts of the world!

Objectives

Students will observe the exterior anatomy of arthropods, specifically the crayfish and the grasshopper. They will observe the similarities and differences between the two species by focusing mainly on the integumentary system.

Arthropod Evolution and Success on Land

  • Evolutionary peak of protostomes
  • Exoskeleton gives support and shapes their bodies (when on land)
  • Small in size
  • Very mobile, insects have wings
  • Waxy cuticle (in arachnids and insects) prevents water loss
  • Stability with a light body and long legs
  • Tracheal system of tubes for respiration, can carry air around body
  • Birth live young, care for them
  • Live in a wide range of habitats
  • No other real competition for food and space

Taxonomy- Crayfish

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Crustacea

Class: Malacostraca

Order: Decapoda

Suborder: Pleocyemata

Infraorder: Astacidea

Superfamily: Astacoidea or Parastacoidea

Taxonomy- Grasshopper

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Hexapoda

Class: Insecta

Order: Orthoptera

Suborder: Caelifera

Crayfish Anatomy Part 1
Grasshopper Anatomy Part 1

Integumentary System- What Holds It All Together

Both crayfish and grasshoppers have an exoskeleton made of chitin. Chitin is a polysaccharide with nitrogen groups. Because they are continually growing, they often have to go through a molting process. This happens about 6 to 10 times in their first year of life but only 3 to 5 in their second, and often last, year. Both arthropods have jointed legs with separate sections, though grasshoppers have 3 pairs of legs while crayfish have 5 pairs. Additionally, their bodies are divided into 3 separate regions: the head, the thorax, and the abdomen, which is also segmented. However, the head and thorax of the crayfish are fused together to create the cephalothorax. The combined exoskeleton acts as a sort of armor that provides protection against predators, support of inner organs, and strength against prey.

Fun Facts

  • There are 3 times as many different species of arthropods as any other animal on Earth, with perhaps millions still undiscovered
  • Have existed for millions of years
  • At any point in time, there are about 1018 (10 billion billion) living arthropods
  • About 3/4 of all living animals
  • 3 pairs of fused cerebral ganglia form the brain
  • Sensitive hairs on their body create a highly advanced nervous system
  • Insects use spiracles for respiration, which is why they're so small
  • Open circulatory system
  • Waste that is excreted is almost completely dry to conserve water
  • Arthro in Greek means "joints" and poda means "legs" (literally called jointed legs)

Human/Ecological Impact

Arthropods are the basis for most food chains and webs, especially the class Insecta. Aquatic arthropods like the crayfish are an important part of those ecosystems, as well as being a source of food for humans. However, terrestrial arthropods such as the grasshopper have the most significant impacts. These insects are responsible for a large portion of the natural pollination of plants and crops. Some insects travel up to 10 miles to find food, so they distribute pollen grains to a wide variety of regions. This is crucial for humans because it saves labor costs of manually pollinating plants. They are also a form of natural pest control. Arthropods, especially arachnids, consume creatures that are pests to humans such as mosquitoes and flies. Although, they can also be carriers of diseases. We humans, however, are not returning their favors very well. Clear-cutting forests and creating suburbs moves into and destroys many of their natural habitats, and commercial fishing can greatly reduce the population of crayfish.