Arthropod Analysis

Anusha De 4/9/14 Vu-PAP Bio- P3

Objective

The objective of this dissection is to examine two preserved arthropods - a grasshopper and a crayfish - and to identify phylum traits (similarities ) and class traits (differences).

Taxonomy

  • Kingdom: Animalia - eukaryotic, multicellular
  • Phylum: Arthropoda - segmentation, bilateral symmetry, jointed paired appendages, chitinous exoskeleton


Grasshopper

  • Class: Insecta - 3 main body parts, compound eyes, metamorphosis
  • Order: Orthoptera - cylindrical body, hind legs
  • Family: Acrididae - short or absent wings, short antennae
  • Genus: Melanoplus
  • Species: Differentialis


Crayfish

  • Class: Crustacea - gills, exoskeleton, filter feeder
  • Order: Decapod - chelipeds, 10 legs
  • Family: Cambaridae - 2 main body parts, large pincers
  • Genus: Cambarus
  • Species: Bartonii

Arthropods at a Glance

The phylum Arthropoda makes up more than 90% of kingdom Animalia. Some characteristics of arthropods are an exoskeleton, jointed appendages, and bilateral symmetry. Two classes within the phylum Arthropoda are Insecta and Crustacea:


Insecta (Grasshopper)

All organisms in class Insecta have bodies divided into 3 parts (head, thorax, abdomen), 6 legs attached to the thorax, two antennae, and lateral compound eyes. Melanoplus differentialis, otherwise known as grasshoppers, are organisms that have olive green, brown, or yellow cylindrical bodies that can be up to 1.75 inches in length. They have enlarged femora (hind legs) which have distinctive black markings. Grasshoppers eat most types of plants, and have a variety of predators. Grasshopper adaptations include enlarged femora for jumping and the ability to detect moisture in the environment (through antennae).


Crustacea (Crayfish)

All organisms in class Crustacea have 2 body regions, 2 pairs of antennae, at least 5 pairs of legs, and are primary aquatic. Cambarus bartonii, otherwise known as crayfish, are organisms that have 10 legs. The front two legs are actually large claws called chellae. Crayfish use their chellae for self-defense and to attack prey.

Evolution

Both the grasshopper and the crayfish have an exoskeleton, jointed appendages, and bilateral symmetry because they are both arthropods. However, arthropods evolution can clearly be seen in the differences between grasshoppers and crayfish. For example, in the crayfish, the 2 front legs have evolved to become a large set of pincers. This is a valuable adaptation for self-defense and finding food. The exoskeleton has evolved to a hard shell on the crayfish's back called a carapace. This is another ecological adaptation that provides protection from the crayfish's numerous predators. Grasshoppers have also evolved to become better adapted to their environment. The hind legs of grasshoppers have evolved into an enlarged femora, which is an important adaptation because it enables the grasshopper to jump away quickly when it is being pursued by a predator. Grasshoppers have also evolved to have a hard exoskeleton with which they can repel enemies.

Anatomy and Dissection

Refer to the following videos and images for an overview of the external and internal anatomy of both the grasshopper and the crayfish, along with guided dissections.
Grasshopper Dissection
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Crayfish Dissection
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The Respiratory System

The function of the respiratory system in arthropods is to deliver oxygen to the cells in the body and remove carbon dioxide. Although their functions somewhat overlap, the respiratory system is separate from the circulatory system. The respiratory system consists of spiracles, tracheae, and tracheoles. Specialized openings in the exoskeleton called spiracles allow air to reach the tracheae. Spiracles can be opened and closed by valves to prevent water loss if needed. Tracheae are a series of cuticle-lined air ducts that branch into tubes that carry oxygen throughout the body. These tubes are called tracheoles. The oxygen carried in tracheoles reaches cells by diffusing across the cell membrane. Carbon dioxide is released when the cells undergo cellular respiration. Each organ in an arthropod's respiratory system performs a different function:

  • spiracles - let air in
  • tracheae - carry oxygen throughout the body
  • tracheoles - carry oxygen directly to cells

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2. Insect respiratory system

Arthropod Ecology

Grasshopper

Grasshoppers are most commonly found in fields, woods, and the edges of water bodies such as ponds, streams, and lakes. In the first food chain below, grasshoppers would be classified as primary consumers because they are consuming grass, the producer. Grasshopper prey includes plants such as grass, weeds, crops, clover, and fruit. Predators of the grasshopper include a variety of animals: birds, frogs, lizards, turtles, raccoons, fish, yellow jackets, snakes, ants, centipedes, dragonflies, and crickets.


Crayfish

Crayfish are most commonly found in wet meadow environments, near farm ponds, in irrigation ditches, and generally any freshwater environment that has heavy soil. Crayfish tend to burrow underneath rocks relative to their size. In the second food web below, crayfish would be classified as secondary consumers because they are consuming honeybees (primary consumers), which are consuming dandelions (producers). Crayfish prey on both plants and animals. Some examples of crayfish prey are worms, insects, fish eggs, frogs, toads, and salamanders. Animals such as raccoons, opossums, snakes, and muskrats are predators of crayfish.

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Human Impact

Grasshopper

Grasshoppers are classified as agricultural pests because they eat so much plant life that they have the potential to devastate entire farms, especially when in groups. Each grasshopper can consume up to half its body weight in vegetation each day. This has happened many times in history, each with horrible results. An example of this, Grasshopper Plague of 1874, can be seen in the link below. To prevent heavy grasshopper infestations, many farmers and gardeners use a biological control protozoan called Nosema loucustae, or a chitin inhibitor called diflubenzuron.


Crayfish

Contrary to grasshoppers, crayfish are widely sought out by humans because they are so good to eat and are easy to find. Overfishing crayfish is a foreseeable problem because in addition to endangering the crayfish, it could severely disrupt the food chain in the crayfish's habitat.

Fun Facts

  • Ancestral arthropods were the first land animals.
  • Arthropods molt their exoskeleton as they grow.
  • All arthropods undergo metamorphosis at some point in their life cycle.
  • Arthropods have been on Earth for 428 million years.
  • Arthropods do not have blood vessels.
  • Arthropods are cold-blooded.
  • Arthropod means 'jointed foot' in Greek.
  • All arthropods have multiple pairs of limbs.
  • Arthropods live in a wide range of habitats, from deserts to oceans.
  • Arthropods have been responsible for the most devastated plagues and famines in the history of mankind.