Relationship of Class Insecta with Other Classes of Arthropoda
Class Insecta, belonging to the subphylum Mandibulata, is the largest and most diverse group of arthropods. Insects share several features with other arthropod classes but also exhibit distinct characteristics that set them apart. Below is a comparative analysis of the relationships between Insecta and other major arthropod classes.
- Relationship with Class Myriapoda (Millipedes and Centipedes)
Similarities:
- Both Insecta and Myriapoda belong to the subphylum Mandibulata and possess mandibles for feeding.
- Both groups have a terrestrial habitat and breathe through tracheae.
- They exhibit segmented bodies and jointed appendages.
- Their nervous system is similar, with a ventral nerve cord and paired ganglia.
Differences:
Feature | Insecta | Myriapoda |
Body Segmentation | Divided into head, thorax, abdomen | Divided into head and trunk |
Number of Legs | Three pairs (6 legs) | Many pairs (Millipedes: 2 pairs/segment, Centipedes: 1 pair/segment) |
Antennae | One pair | One pair |
Wings | Usually present | Absent |
Eyes | Compound eyes | Simple eyes |
Feeding Habit | Herbivorous, carnivorous, omnivorous | Millipedes: Herbivorous, Centipedes: Carnivorous |
- Relationship with Class Crustacea (Crabs, Lobsters, Prawns)
Similarities:
- Both belong to the subphylum Mandibulata, meaning they have mandibles for chewing food.
- Their bodies are segmented, and they have jointed appendages.
- Both exhibit chitinous exoskeletons that require molting for growth.
- Some primitive insects, such as silverfish (Thysanura), share features with crustaceans.
Differences:
Feature | Insecta | Crustacea |
Habitat | Mostly terrestrial | Mostly aquatic |
Number of Legs | Six legs (3 pairs) | Five or more pairs |
Antennae | One pair | Two pairs |
Appendages | Uniramous (unbranched) | Biramous (branched) |
Respiration | Tracheal system | Gills |
Eyes | Compound eyes (on head) | Compound eyes (often on stalks) |
Some crustaceans like isopods (pillbugs/woodlice) are terrestrial, showing an evolutionary link between aquatic and land arthropods.
- Relationship with Class Arachnida (Spiders, Scorpions, Ticks, Mites)
Similarities:
- Both belong to phylum Arthropoda, exhibiting segmented bodies, exoskeletons, and jointed legs.
- Both have a ventral nerve cord and compound/simple eyes.
- Many arachnids and insects have tracheal respiration or book lungs.
- Some arachnids and insects are predators (e.g., spiders and praying mantises).
Differences:
Feature | Insecta | Arachnida |
Body Division | Head, thorax, abdomen | Cephalothorax and abdomen |
Number of Legs | Six legs (3 pairs) | Eight legs (4 pairs) |
Antennae | Present (one pair) | Absent |
Wings | Present in most | Absent |
Mouthparts | Mandibles (chewing, sucking, piercing, etc.) | Chelicerae (fangs, pincers) |
Respiration | Tracheal system | Book lungs/tracheae |
Insects and arachnids both have chitinous exoskeletons, but arachnids lack antennae and wings, making them quite distinct.
- Relationship with Class Merostomata (Horseshoe Crabs)
Similarities:
- Both are arthropods with exoskeletons and jointed appendages.
- Both exhibit segmentation and molting (ecdysis).
- Horseshoe crabs have compound eyes, like insects.
Differences:
Feature | Insecta | Merostomata |
Habitat | Terrestrial | Aquatic (marine) |
Body Structure | Three-part division (head, thorax, abdomen) | Cephalothorax and abdomen |
Number of Legs | Six legs (3 pairs) | Five pairs (10 legs) |
Antennae | One pair | Absent |
Respiration | Tracheal system | Book gills |
Horseshoe crabs are more closely related to arachnids than insects.
Conclusion
Class Insecta is closely related to Myriapoda and Crustacea due to their shared mandibulate characteristics but differs significantly from Arachnida and Merostomata, which belong to Chelicerata.
Evolutionary Perspective:
- Crustaceans and insects share a common ancestor and are sometimes grouped under Pancrustacea, indicating a closer relationship.
- Myriapods and insects share similarities in their terrestrial adaptations, but insects evolved wings and more complex sensory structures.
- Arachnids and merostomes are more distantly related to insects due to their chelicerae-based feeding and lack of antennae.
Insects are the most successful arthropods due to their ability to fly, diverse feeding habits, and adaptability to various habitats.
