Lab Report Comparing the Anatomy of Crayfish and Grasshopper
Introduction
The aim of the investigation is to compare and contrast the external anatomical characteristics of two classes of the Phylum Arthropoda, Class Crustacea and Class Insecta. A crayfish was used to represent the Class Crustacea and a grasshopper was to represent the Class Insecta.
Arthropods are the most abundant and diverse group of animals on the planet. The organisms in this Phyla share common characteristics which include: the body of most arthropods is covered with chitin hardened into an exoskeleton. In crustacean, the chitin is hardened by calcium. In insects, the chitin is tanned, chemically bonded with protein. The bodies of arthropods are made of many segments. They have jointed appendages which are modified into many specialized organs used for grasping, walking and eating. Arthropods have a double ventral nerve cord with ganglia at each segment. The brain ganglion is located above the digestive system. They have an open circulatory system. Blood flows through a dorsal vessel towards the brain. The open system allows blood to flow back through the body. Arthropods are bilaterally symmetrical. The body is divisible into two equal parts through one plane. They reproduce through sexual reproduction. This involves the uniting of male and female gametes. However, some insects reproduce without mating. Haplodiploidy is common among the honey bee.
Insects fall under the Class Insecta. They have three body parts, i.e. head, thorax and abdomen, three pairs of legs that are attached to the thorax, one pair of antenna connected to the head, mouthparts which are modified for sucking or chewing, and two pairs of wings. Other insects may have one pair of wings or may be wingless. They breathe through spiracles and have an open circulatory system. Crayfish fall under the Class Crustacea. The body of a crayfish is divided into two main parts, i.e. the cephalothorax and the abdomen. The cephalothorax includes the head and the thorax. The abdomen is flexible and ends at the telson. They have two long antenna and two shorter antennules located between the antennas. They have mouthparts modified for biting and chewing. They have four pairs of walking legs attached to the thorax. In addition, they have chelipeds, which they use for defense and to capture prey. Crayfish breathe through gills and blood flows through an open circulatory system.
- Lab apron
- Gloves
- Eyeglasses
- Dissecting kit with forceps and scalpel
- T-pins
- Magnifying glass
- Preserved grasshopper
- Preserved crayfish
- Paper
- Pen
Procedure:
- Preserved grasshopper and crayfish were obtained and placed on the dissecting pan.
- It was observed that the grasshopper has three body parts while the crustacean has two body parts. The body parts of these two organisms were labeled.
- The heads of the two organisms were located and the different parts labeled. These included: the antennae, the eyes and mouth parts.
- Forceps were used to remove the appendages from the head
- The appendages on the thorax were examined and their different functions noted.
- Forceps were used to remove the walking legs and the different parts identified and labeled.
- A magnifying glass was used to locate spiracles for respiration on either side of the abdominal segments.
- Using forceps, the carapace on either side of the crayfish were lifted and the gills (for respiration) noted.
Discussion:
Following the steps outlined in the procedure several differences and slight similarities were observed in the external anatomies of the crayfish and grasshopper. Grasshoppers have three body parts namely head, thorax and abdomen. Crayfish have two body parts namely cephalothorax and abdomen. The cephalothorax comprises of the head and the thorax. Their exoskeletons are both made of chitin and serve to offer protection especially from dessication.
Grasshopper
Crayfish
A slight difference is observed in their number of antennas. The grasshopper has a single pair while the crayfish has two pairs. The first pair of the crayfish is homologous to that of the grasshopper and is for sensory function, the second pair is not homologous. A glaring difference is the presence of two pairs of wings in the grasshopper. The first pair is called the mesothoracic wings. They are narrow and leathery. The second pair is called the metathoracic wings. They form the hindwings and lie beneath the mesothoracic wings. They are folded and thin.
Both organisms have compound eyes. The grasshopper has two compound eyes. It is nonetheless important to note that the grasshopper also has three simple eyes-ocelli-located between the compound eyes. The mouth parts of the two are largely similar as both have mandibles and maxillae with the grasshopper also possessing a labium and labrum. Crayfish have a pair of mandibles, two pairs of maxillae, and three pairs of maxillipeds. Grasshoppers have two mandibles and two maxilla in addition to having one labrum and labium.
Crayfish Mouthparts
Grasshopper Mouthparts
The thorax of the crayfish is divided into five segments each with a pair of legs. The first pair of legs is called the chelipeds, which they use for defense. The remaining four pairs of legs are used for walking. The grasshopper has three pairs of legs in the thorax. The first two pairs are used for walking while the last pair is used for jumping. Respiration is carried out by different structures in the two, the difference brought about by their environments-terrestrial and aquatic. The grasshopper has eight pairs of spiracles in the abdominal segments. Gills are observed under the carapace in the crayfish with some extending to the thorax.
In both organisms, there are slight differences in the abdomens of the male and female. In the grasshopper, the male has a rounded abdomen while the female has a tapered abdomen ending in an ovipositor (egg laying tube). In the crayfish, the telson (last segment of the abdomen) in males is pointed while that of the female is broad.
Conclusion:
As pointed out, the crayfish and grasshopper have several similarities and differences in their external anatomy. Their similarities highlight the fact that they are in the same phylum arthropoda- they both have jointed appendages, their bodies are divided into segments and have an exoskeleton of chitin among other similarities.However, their differences necessitated the need for their classification into different classes. Class Crustacea are divided into two body parts, are wingless and undertake respiration with gills while Class Insecta are divided into three body parts can be winged or wingless and undertake respiration with spiracles.
Works Cited
Alcamo, Edward and I. Edward Alcamo. Biology Coloring Workbook. New York: The Princeton Review, 2007.
Capinera, John L. Encyclopedia of Entomology. New York: Springer, 2008.
Coulson, Robert N. Forest Entomology: Ecology and Management. New York: John Wiley & Sons, 2006.
