Classifying the Roly Poly bug

Phylogenetic Tree image courtesy of WikiMedia Commons

Armadillidium vulgare

Domain: Eukarya
The domain Eukarya evolved from the first prokaryotic organisms more than 1.7 billion years ago. Organisms under  the domain Eukarya have a true nucleus and membrane-bound organelles.  

Kingdom: Animalia
Animalia is an extremely diverse kingdom containing more than 1.5 million different species of animal. Armadillidium vulgare fall under the kingdom Animalia because they are not autotrophs and instead rely on other organisms as a food source (Encyclopedia 2013).

Phylum: Arthropoda
The arthropods are characterized by the bilateral symmetry of their bodies, segmented bodies with jointed appendages and a chitinous exoskeleton.  In order to grow, all arthropods undergo ecdysis, or molting, in which they shed their exoskeleton in order to have a new, larger one.  A.vulgare is an arthropod because it fulfills all of these characteristics, including ecdysis as shown below.

Class: Malacostraka
Armadillidium vulgare follow the general body plan of Malacostraka in that their bodies have three parts to them: a head (cephalon), thorax (pereon) and abdomen (pleon).  Inside their bodies they have a two chambered stomach and appendages on their abdomens called pleopods that are used for swimming, brooding eggs and catching food.  They have a centralized nervous system with a brain and ventral nerve cord.  A. vulgare fits into this class because it possesses all of these features (Discover Life in America 2010).

Order: Isopoda
Isopods have two sets of antennae and compound, sessile eyes (meaning they are not on the end of appendages, such as a crayfish’s eyes are).  They undergo ecdysis (molting) in two phases and have four sets of jaws (Tree of Life 1997).  The isopods use their pleopods (appendages on the abdomen) for swimming, brooding eggs, catching food and, specifically, as gills for breathing (Discover Life in America 2010).  A. vulgare display all of these characteristics.

Family: Armadilliidae
Most within the family Armadillidiidae are characterized by an hour-glass shaped telson.  A telson is the last segment in the abdomen of a crustacean (the subphylum of A.vulgare is Crustacea). A. vulgare also falls under this family because it has pigmentation patterns throughout its thorax, or the part of the body between the head and the abdomen (British myriapod n.d).

Armadillidium vulgare on patrol. Photo by Jeremy Royall, used with permission.

Genus: Armadillidium
The organisms within the genus Armadillidium lack a waxy cuticle layer to retain moisture within their bodies; this is the main reason why A.vulgare is nocturnal. Those within Armadillidium have seven pairs of legs, as opposed to those in the class Insecta, which only have three pairs.  Additionally, Armadillidium organisms are loosely classified under a size of approximately 15mm (Biotic Inventory 2010).  

Species: Armadillidium vulgare
The scientific name Armadillidium vulgare translated from Latin to English means common woodlice.  

Phylogeny of Opisthokonta. General tree created by the author.

The above phylogeny is a representation of different phyla within the major clade Opisthokonta based on morphological traits.  Armadillidium vulgare falls under the phylum Arthropoda due to its bilateral symmetry, chitenous exoskeleton and segmented body among other relative traits. 

Phylogenetic tree of isopod Wolbochia strains.  From the article "Evidence for a new feminizing Wolbachia strain in the isopod Armadillidium vulgare: evolutionary implications" (Cordaux 2004)

This particular phylogeny is based on strains of Wolbachia in specific species of isopods (for explained relationship with A.vulgare, visit the Interactions page).  Wolbachia is an endosymbiotic bacteria that has mostly parasitic interactions with the isopods in which it lives.  In A.vulgare specifically, Wolbachia suppresses important aspects of its immune system.  This phylogeny was determined through PCR-based studies of Wolbachia hosts (Cordaux 2004).

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