Members of the Kingdom Animillia are multicellular and rely on other organisms to obtain food and nutrition. Octopuses lack compnents like cellulose that would classify them as a plant and have a complex and relative movement that classifies them as animilia.  Affiliates of this Kingdom also reproduce sexually and their development contains distinct stages such as a zygote like the E. megalocyathus or Emu (Myers, 2001).

The word Mollusca is derived from the Latin word Mollusscus, meaning soft (Barney, 2000). There is huge amount of variety in this group so it is difficult to apply a characteristic to every member.  Two main characteristics of this phylum include the assembly of the nervous system and a mantle that contains a major cavity for breathing and excretion.  Members tend to have no backbone and an internal cavity that contains the heart, gonads (organ that produces gametes) and kidney.  A shell composed of proteins and chitin that is strengthened with calcium carbonate and buried by the mantle that covers the entire superior surface is another common characteristic (Barney, 2000).  Other members of this phylum are the terrestrial snail and tapered vertigo.

Figure 2. The Phylum Mollusca is classified into seven different classes based on major morphological and anatomical features with the major synamorphy being conchifera, meaning shell bearing.  Each of the seven classes' names are constructed based on their plates/shells. Class Cephalopoda is then divided into seven orders based on their morphological features.  Karlissa McAtee 2013.

        The first class Aplacophora, means “without plates,” having no shell, head or mantle and instead having spicules. Bivalvia means “two valves” and also has no head with their foot extending through the two valves (Barney, 2000). Cephalopoda means “head-footed” and consists of organism that have a distinct head and great complex eyes. This group does not have an external shell and their “foot” is a set of arms that circle around the mouth. Our organism E. megalocyathus is classified into this group due to having all the features I just named. Another class called Gastropoda means “stomach foot,” having a large foot and a developed head with eyes and tentacles. Monoplacophora means “bearing one plate,” while also having bilateral symmetry with a head, foot, mantle and radula (Barney, 2000). The sixth class has no eyes, tentacles or radula and is called Polyplacophora means “bearing many plates.” It is a flat Mollusca that consists of eight overlapping shells (Barney, 2000). The final and eighth group is Scaphopoda meaning “boat-footed,”  having a tusk shaped shell with eyes, gills and tentacles (Barney, 2000).

       The class Cephalopoda is classified into seven different orders based on three major synamorphies. One of them is Nautiloidea, where all of the organisms possess a simple concave septa and siphuncle in which the septal neck points to the rear. Another one is Ammonidea, which consists of an extinct group of marine invertebrate animals that are more closely related to Coleodiea then Nautiloidea. The synamorphy Coleodiea, means similar to a sheath or scrotum and has no outer shell (Barney, 2000). The orders Octopoda, Sepiolida, Teuthida and Vampyromorphida are all classified within this synamorphy. Under Octopoda is where our organism E. megalocyathus resides, being classified within this group.

Class- Cephalopoda

This class contains some of the most intelligent invertebrates such as E. megalocyathus and many other octopui, as well as the humboldt squid.  Cephalopoda means "head foot" where their arms and funnels are byproducts of their foot.  An octopus is classified into this class because they have a completely merged head and foot along with a ring of tentacles that surround their head (Wheeler & Fautin, 2001).  Members of this class are usually carnivores and contain chromatophores that cause them to change color (Wheeler & Fautin, 2001).  They are also gonochoric meaning that they have one of at least two distinct sexes in one individual.  Affiliates of this class move by walking with their tentacles or jet propulsion, a propelling force of a backwards ejection of a high speed spurt of liquid.

Order - Octopoda

Octo means eight and poda means "those having feet."  This order is comprised of those with eight legs, like an octopus that does indeed have eight arms or "legs."  Benthic species like E. megalocyathus are generally what make up this order and also have a short and compact body, arms with suckers and a funnel.  Members of this order also contain a viscera, meaning their internal organs are in the main cavity of the body.