Question

Which class of arthropods includes the crabs and lobsters?

• A. Insecta
• B. Crustacea
• C. Arachnida
• D. Myriapoda

Answer 1

Answer:

B. Crustacea

Understanding Crustacea: The Class of Crabs and Lobsters

• The class Crustacea belongs to the phylum Arthropoda, which is the largest phylum in the animal kingdom, characterized by an exoskeleton, segmented body, and jointed appendages.
• Most crustaceans are aquatic, found in marine and freshwater environments, though some are terrestrial (e.g., woodlice).

• Key Characteristics of Crustacea:

  • Exoskeleton: They possess a hard, protective outer shell made primarily of chitin, often reinforced with calcium carbonate, which provides support and protection. This exoskeleton is shed periodically through a process called ecdysis or molting.
  • Respiration: Respiration typically occurs through gills, adapted for extracting oxygen from water.
  • Body Segmentation: The body is generally divided into two main regions: a fused cephalothorax (head and thorax combined) and an abdomen.
  • Appendages: A distinguishing feature is the presence of biramous appendages (meaning they have two branches), unlike the uniramous appendages of insects and myriapods. These appendages are highly specialized for functions like walking, swimming, feeding, and sensory perception.
  • Antennae: Crustaceans possess two pairs of antennae, which are primarily sensory organs used for touch, taste, and smell.
  • Compound Eyes: Many crustaceans have compound eyes, providing a wide field of vision.

• Examples of Crustaceans:

  • Common examples include crabs, lobsters, shrimp, prawns, krill, barnacles, and crayfish.
  • The Japanese spider crab (Macrocheira kaempferi) is notable for having the largest leg span of any arthropod, reaching up to 3.7 meters.
  • Daphnia (water fleas) and Copepods are microscopic crustaceans that form a vital part of the zooplankton, serving as a primary food source in aquatic food webs.

• Ecological and Economic Importance:

  • Crustaceans play crucial roles in aquatic ecosystems as both predators and prey, contributing significantly to nutrient cycling.
  • Many species, like crabs, lobsters, and shrimp, are of significant economic importance globally as a valuable food source for humans, supporting large-scale fishing industries.

• Distinction from other Arthropod Classes:

  • While sharing common arthropod features, Crustacea differ from classes like Insecta (six legs, usually wings, one pair of antennae, uniramous appendages), Arachnida (eight legs, no antennae, body divided into two tagmata), and Myriapoda (many segments, many legs, one pair of antennae).