Classification of the Polyrhachis lamellidens:

In order to become more familiar with this organism it is important to first understand what the scientific name of it means. In order to do this lets break it down into separate parts. 

           Poly=many,    rhachis=spine,    lamelli=thin plate,    dens=shoulder. 

 

 

Domain: Eukarya - This organism falls under the domain eukarya, because it contains a cell with a true nucleus, multiple linear chromosomes, and membrane bound organelles.  This organism also falls under this domain due to its capacity to reproduce sexually.

 

Kingdom: Animalia - It falls under this classification due to its lack of a cell wall. Without the restriction of a cell wall this organism is able to move quickly and freely.  One key attribute in its membership to the animals is that its life cycle does not involve a multicellular haploid stage, which means it does undergo an alternation of generations.

Phylum: Arthropoda -   All members of this phylum possess segmented bodies that are separated into distinct head and trunk regions.  A defining characteristic of this phylum is the presence of a protective outer covering called an exoskeleton, which in the Polyrhachis lamellidens is made up of a substance called chitin.

Class: Insecta - One key reason why this organism is classified as an insect is due to the process by which it sheds its chitinous exoskeleton as a means for growth and development.  More key classification features are its three pairs of legs found on the thorax and the three body sections known as the head, thorax, and abdomen.

Order: Hymenoptera - Members of this group are unique in that they all undergo complete metamorphosis.  The larva of the Polyrhachis lamellidens look completely different from the adult form. Organisms also possess chewing mouthparts, bent antennae, and in most cases a pair of wings.

 

Family: Formicidae - Members of the Formicidae live in colonies that divide labor between the sterile worker ants, the reproductive males, and the reproductive queens.  The ants that are able to reproduce also possess wings that are used in nuptial flights (explained later).

 

Genus: Polyrhachis - The most significant classifying features of this genus are the number of spines it possesses, the place of the spines, and form of the spines located on its dorsal region.  The Polyrhachis ants also share commonalities in the form of compound eyes, width of the head, and the arch of the head region.

Species: Polyrhachis lamellidens - Worker ants of this species have black colored heads, abdomens, and appendages.  They also possess a very well-armoured thorax that has a dark orange appearance.  The dorsal region of the thorax possess a pair of propodeal shoulders that form a pair of backwards spines.  One of the most recognizable features of this species are the two long spines that curve outward off of the petiole.

Phylogenetic Trees:

The phylogenetic tree pictured to the right was constructed using molecular data collected from small subunit ribosomal DNA.  The Polyrhachis lamellidens is a member of the kingdom animalia which is located directly under the domain eukarya.  All members of the eukarya share a few commonalities in that their cells possess a true nucleus and contain membrane bound organelles.  The tree above displays the animals and the fungi diverging from a common ancestor around 650-900 million years ago.  The significance of this is that the animals are actually more closely related to fungi than any other kingdom.  While evolution has created extreme diversity among these two kingdoms in the last 700 million years, fungi and our friend the Polyrhachis lamellidens do share one very special trait in common.  Ants along with many arthropods experience protection from an exoskeleton made up of chitin, and the main component in the cell walls of fungi is also chitin.  This shared derived characteristic is one key feature that links these two kingdoms together and supports the notion of a monophyletic relationship.

The phylogenetic tree to the left specifically deals with the relationship between different families of ants.  This phylogenetic tree was constructed using molecular data from DNA sequences featuring the nuclear genes 18S, 28S, and EF-1alpha.  The Polyrhachis lamellidens is a member of the subfamily Formicinae.  This tree shows that the closest relatives of the Formicinae are members of the subfamily Myrmicinae and Extatomminae.  These three subfamilies represent a monophyletic relationship, which means that they all share one common ancestor.  These subfamilies have derived many new characteristics since their divergence.  One unique feature that ants from both of these subfamilies share is that members of these two subfamilies build their nests in trees or in rotting wood.  One key difference between these two ants is the presence of a cocoon around the pupae of the Formicinae, and the pupae of the Myrmicinae lack the presence of cocoons.

 

 

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