Every animal has a body composition that is fit and adapted to the habitat that they reside within. Photinus marginellus species live within the terrain of the woods and underneath the cover of leafy underbrush. To fit in with this environment that can change from hot/tropic to cold the Photinus marginellus need to have a body that can adapt to any type of environment they migrate to. Different things such as their chitonous exoskeleton, appendages, and light organelles help Photinus marginellus navigate within their environment. These means of adaptation all play a role to help in their survival.
         A distinct feature of being an insect is having a exoskeleton. An exoskeleton is comprised of chitin and is found on the outside of an insect, by means of protection. (Click here for another organism who has a chitonous exoskeleton). The exoskeleton is an attachment site for muscles and provides support for the whole organism. Most Insects with an exoskeleton require a process called molting. For the Photinus marginellus molting occurs during each stage of its life process or cycle by ridding of the exoskeleton that is currently has to make room for the new skeleton that is underneath it, which allows the firefly to grow bigger. The only down side to this part of their life cycle is that after the molting has occurred, the Photinus marginellus is then vulnerable because of the new exoskeleton it obtained due to the skeleton not yet strengthened or hardened enough to protect the insect properly (Hadley, Debbie, 2013).   
    The Photinus marginellus has two different styles of exoskeleton which has been caused by a mutation. The first style of exoskeleton that the Photinus marginellus possesses is an exoskeleton with a dark pattern on the top. The dark area on the top has a black area on the inside surrounded by a yellow outline. The other style is a light pattern that is the same as the other darker pattern except instead of a black color on the top, the color is more of a light brown to a tan. These differences in color are due to an evolutionary mutation. Both insects seem to survive equally well  (Luk et al, 2011).  The Photinus marginellus exoskeleton has many other purposes than color.

 Courtesy of Wikipedia
                                                                                                                                                                                                                              Figure 1. Depicts the distinct body regions of the Photinus pyralis, which is closely related to Photinus marginellus. This photograph shows the sheath wings. The uppermost wing is hard for protection, while the bottom wing remains flexible for flight. 

 *Exoskeleton advantages:                                          *Exoskeleton Disadvantages
-covers the muscles and other                                     - limits the possible size of the animal
 soft tissues from harm.                                               -Surface area to volume ratio is limited
- Better protected against immediate attacks
- The outer layer is very strong and resists
          Aside from providing colors to the organism, The Photinus marginellus exoskeleton has more beneficial purposes. The exoskeleton for the Photinus marginellus is the attachment site for six jointed or segmented legs, two antennae, and a divided body that consists of three different parts that are called the head, thorax and the abdomen.
           The head houses both the antennae, which are used to find food and notice enemies, along with housing the eyes. Photinus marginellus has compound eyes which have multiple light-sensitive sensors and each one has its one refractive system that helps to form part of the entire image (Farlex, 2013; Luk et al, 2011).  The compound eye is very beneficial to Photinus marginellus because the eyes are able to pick up more light and movement faster than a simple eye. This gives the Photinus marginellus a faster reaction time, which is good because of its small size (Museum of Science Boston, 2013).
          Photinus marginellus uses its six segmented legs to crawl around the forest environment which it inhabits. The six segmented legs are found on the thorax; the middle section of the body, along with the wings and the light organelles in the back of the abdomen to help with mating signals and mimicry (McKenzie, J. 2001).  The thorax is the main site and adaptation for movement. The legs are all segmented which allow for a full range of motion that help the firefly move throughout its terrestrial environment by way of walking or crawling. Next are the wings that are used for flying. The outermost wing is called Elytra which is a hard front wings that serve as protective covers for membranous hind wings. The back wing is the more flexible wing which is used for flight(Fig 1) (Kinsey, B., 2005; Museum of Science, Boston, 2013). 
            The last section of the organism is the abdomen. The abdomen is segmented and also happens to be where the light organelles are located. (See the Reproduction page for more information on the benefits of the light organelles). The light organs are the way to tell the difference between the male and the female. The light organelles of a female Photinus marginellus is located only on the second to last section of the abdomen (Fig 2). The male light organelle is located on the last two sections of the abdomen (Museum of Science of Boston, 2013).  To find out more information and for a better understanding on how to read a flash chart try going to the Museum of Science, Boston website. The flash chart shows the different ways that the Photinus marginellus use the light organelles to communicate. Another place to look for more information about different body plans and see amazing pictures that have both Photinus marginellus and others fireflies look into the Canadian Journal of Arthropod Identification, "The Fireflies of Ontario (Coleptera: Lampyridae)" it will show you more of the connections between different species of Photinus based on different body parts and body plans.

Permission granted by Tom Murray

Figure 2. Shows the Photinus marginellus and the light organelles located in the abdomen. This figure distinguishes this particular Photinus marginellus is a female due to the light organ only visible on the second to last section of the abdomen.

      Without the protective exoskeleton, the Photinus marginellus would not be able to function physically. The exoskeleton allows for this locomotion, but the nutrients for growth are just as important for physical health of the organism.  Check out the nutrition page to find out what the Photinus marginellus eats to obtain its essential nutrients!

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