Skip to main content

#6: What defines an insect?



A general overview of arthropod body plans and phylogeny (relationships) of the four extant groups. <https://dev.biologists.org/content/129/5/1225/F1>

 Litinsects #6: What defines an insect?

I realize I’ve been throwing around words like arthropod and insect but maybe not everyone knows how these groups are related. Today I'm going through some classification basics.

First off, insects are ARTHROPODS, meaning they have paired JOINTED LIMBS. Arthropods include 5 main subgroups: (Future posts will go into each of the other arthropod groups in more detail...)
    • (1) Trilobites, which are extinct
    • (2) Chelicerates, which include spiders, scorpions, and mites
    • (3) Myriapods, consisting of millipedes and centipedes
    • (4) Crustaceans, including lobsters, crabs, and barnacles
    • (5) Hexapods, the group to which insects belong

  • Arthropods have a hard EXOSKELETON made of chitin that supports and protects the body. All arthropods grow by MOLTING, a process by which they shed their exoskeleton known as ECDYSIS

There are some defining anatomical features that ALL INSECTS have in common:


  • Different groups of arthropods vary in the number of leg pairs. Insects belong to the subgroup HEXAPODA since they have 6 LEGS!

  • The hexapods are divided into 2 groups, differing in the position of their mouthparts. All insects, aka Ectognatha from ecto “outside” and gnathos “jaw”, have EXTERNAL MOUTHPARTS. The other hexapod group is Entognatha, from ento “inside” and gnathos “jaw”, which have mouthparts recessed into a pouch in their heads. These include Collembola, Diplura, and Protura, all of which are apterous (wingless)

  • The insect body plan includes 3 basic units: 
    • (1) the HEAD, which include the eyes, antennae, and mouth parts
    • (2) the THORAX, to which the 6 legs and wings attach
    • (3) the ABDOMEN, which contains most of the reproductive, digestive, respiratory, and excretory structures

  • Each body unit is divided into segments. The word INSECT comes from the Latin insectum meaning “cut up” or “segmented”. With the word ENTOMOLOGY, it’s basically the same thing only in Greek; entomon means “cut into pieces” which then became the Greek word for insect.

I hope this cleared up some of the relationships among these groups and gave you a better idea of what actually defines an insect. TAXONOMY, or the classification of organisms, is a very interesting but very complex field. Some evolutionary relationships are still not fully understood or are constantly changing with new data. Scientists do their best to classify species based on most recent knowledge but these are not necessarily set in stone.

Thanks for reading... more to come tomorrow!
Labels:

Comments

Post a Comment

Popular posts from this blog

#13: Insect Legs

Litinsects #13: Insect Legs Insect legs can be as diverse as the animals themselves. Some are long and slender like a crane fly’s, some are short and hefty like a mole cricket’s. But what all insects share is the number and layout of those legs. Hexapods have 6 LEGS, a pair each of fore, mid, and hind legs that are made up of the same basic units. Starting closest to the body, they are:  (1) the coxa, which attaches the leg to the thorax  (2) the trochanter (3) the femur, which is oft en the thickest segment  (4) the tibia, often covered in tiny hairs (5) the tarsus, which contains 5 “pseudo-segments”  (6) the pretarsal claws, of which most insects have 2 on each leg The basic units of the leg always occur in this order but may be reduced or highly modified in some species to fit certain tasks such as running, digging, swimming, grasping, or jumping. This photo sums it up perfectly: from < https://wiki.bugwood.org/File:Insect...
Post a Comment
Read more

WELCOME: Social Distancing Entomology Course

All week I’ve been seeing videos and posts of the creative stuff people have been doing while social distancing, all the while thinking, what could I contribute to all the people sitting at home on social media all day?? Well this morning it hit me. I will do what I do best! And that is... drop some nerd knowledge on you all 🤓 Welcome to my social distancing ENTOMOLOGY COURSE!  Every day I will post an insect photo, most of which I’ve taken through my microscope, and explain about the insect group or the feature pictured. My hope is that you might learn something new about insects and maybe, just mayyyyybe, be a bit more fascinated and a bit less grossed out by the most diverse and arguably most successful group of animals to ever live... thanks for reading, stay tuned 🦋 🦟 🦗 🐞 🐜 🐛
Post a Comment
Read more

#22: Caterpillars

Litinsects #22: Caterpillars Since you are freshly familiar with metamorphosis from my last posts, I will today be talking about caterpillars 🐛 and some structures that change drastically in appearance from before to after metamorphosis: legs. Caterpillars are the worm-shaped larval stage of butterflies and moths. They have huge appetites; they mainly feed to grow and gain energy for their transformation into adulthood. In order to do this they need to get around, for which they use le gs because only adult stages have wings.  But insects only 3 pairs of legs, right? So where do all these extra legs come from all down the sides of their bodies?  Caterpillars have 3 pairs of TRUE LEGS, attached to their thorax, which are jointed and have little claws on the end. These legs are still present after metamorphosis, though they will have changed substantially Additionally, they usually have 2 to 5 pairs of PROLEGS, which are protrusions fr...
Post a Comment
Read more