When classifying organisms, scientists follow a specific method. They organize them into groups and then smaller subgroups of that group. In this classifying system they follow the order Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. 

The harp seal is classified as follows:
Domain: Eukarya
    Kingdom: Animalia
        Phylum: Chordata
            Class: Mammalia
                   Order: Carnivora
                        Superfamily: Pinnipedia
                            Family: Phocidae
                                Genus: Pagophilus
                                    Species: P. groenlandicus
Due to the fact that the harp seal has cells that contain complex structures within a membrane, it is classified as eukaryotic.
From there they are classified as Animalia because harp seals are multicellular, heterotrophic (meaning they consume other organisms for nutrition), lack cell walls, and most exclusively to animals their embryos pass through a blastula stage. The blastula stage is the early stage of development where an embryo is a “hollow” ball of cells created when the fertilized egg goes through cell division called cleavage.  (Animals are a part of the supergroup Unikonta then the sub-supergroup Opisthokonta because the reproductive cells have a single flagella at base).
Harp seals are then classified as Chordate because at some stage of development they contain these five characteristics:  a notochord (also known as a skeletal rod), a dorsal, tubular nerve chord, pharyngeal pouches (also known as gill slits), an endostyle (which in the most basic terms can be described as a pre-thyroid gland), and lastly a post-anal tail. These are not the only characteristics of chordates, but they are the only ones that are uniquely applicable to chordates alone.

     chordata tree
     Diploblasty: two kinds of body tissue, ectoderm and endoderm
     Triploblasty: three kinds of body tissue, ectoderm, endoderm, and mesoderm
     Radial symmetry: can be split in more than 2 ways providing equal halves.
     Bilateral symmetry: only one way to split organism and create equal halves.

Next harp seals are classified in the order Carnivora because they consume other organisms that are heterotrophic. Even more simply stated, they are carnivores because they eat the meat of other organisms, not plants.

From there they are considered to be a part of the superfamily Pinniped, which literally means “fin foot” because they use their fins as feet for locomotion on land.

The family that harp seals are considered to be a part of is known as Phocidea or the earless seals due to the fact that they do not have true ears on their heads. Sometimes animals in this family are called crawling seals in order to set them apart from the fur seals and sea lions of the family Otariidae.

Finally the genus they belong to is known as Phagocillus because it is a harp seal, and they are not closely related to any other marine mammal. Recently they have been made into their own genus because they are less related to other marine species than scientists once thought they were. Previously harp seals went under the genus Phoca along with some other seal types.

The scientific name is Phagocillus groenlandicus because most harp seals can be found in Greenland. It literally means "ice-lover from Greenland", or if you are looking at its synonym Phoca greolandica that means “Greenland seal”.  They were then given their common name after the dark harp shaped mark that is displayed on the backs of organisms belonging to this species.

 phylogeny of seals
 SM Carr & HD Marshall, unpublished data 2004
    This phylogenetic tree demonstrates that, according to a molecular systematic classification, harp seals are no longer known as Phoca greolandica because they are in fact not as closely related to the hood seals, or Phoca vitulina as morphological trees would suggest. They are actually more related to the Histriophoca or spotted seals.

If you would like to learn about the adaptations of the harp seal, follow this link! ADAPTATIONS