The subphylum Unitary or Uterine Parietale is a well-known group of animals, with the exception of some taxonomic groups. As a subphylum, Uniramia belongs to Metatheria, a class that also includes several fishes. These include the sculpin skate, pufferfish, flathead catfish, devilfish, arowanas, damselfly, and many others. The most common fishes in this class are the leopard catfish, shark, piscivorous sharks, rainbow runners, and rainbow trout. All of these have evolved into adult forms.
The subphylum Arthropoda is even smaller, with only three recognized categories: crustaceans, eukaryotic crustaceans, and cephalopods. Among these, crustaceans are by far the most common, with over 50% of all crustaceans being arthropods. They also represent the largest part of the animal kingdom, which is why they are often classified under the phylum Chondrichia. Eukaryotic crustaceans belong to the class Protista. Cephalopods are not true crustaceans, as they lack an internal skeleton. This classification was made because these animals lack both a shell and an external one.
The subphylum Chondrichia has a few representatives in the animal kingdom, which are the common shrimp, leeches, and annelids. This class also includes some freshwater crustaceans like the puffed seaweed, Harlequin shrimp, and stone shrimp. Other crustaceans of this subphylum are the Harlequin shrimp and the annelids. The crustaceans of the subphylum Cephalopoda are the most diverse, with more than seven hundred species known. This includes the popular cephalopods such as the scalloped and boxcar snails.
The subphylum Vascularifera has representatives in the kingdom Protista as well as the Metazoa phylum, which is both present on earth. Vascularifera arthropods have elongated bodies and are usually found in freshwater. They are very diverse and possess a variety of appendages, but their most prominent member is the terminal flippers or claws. These appendages end in claws which are used for walking and moving about.
All crustaceans have paired pairs of antennae, with the exception of the tube worms. The antennae are situated above the mouth, while the paired pairs of antennae form the head. The body of crustaceans is generally divided into limbs, which are held together by soft stomach tissue. These limbs then proceed to form the various legs that are found in the animal.
The subphylum Prototheria also consists of two representative categories: the Prototheria unguium and the Prototheria gigas. Both these species possess elongated bodies, with the prothallium being considerably shorter than its palatal counterpart. The prothallium has an extended pair of antennae. Other notable features of this subphylum are the presence of compound eyes and the presence of several segments in the body.
Subphylum Ustularia consists of only two representatives:
the uninvited terrestrial mollusks (urchin-like crustaceans) and the encrusting terrestrial mollusks. Ustularians do not have compound eyes, since they do not have any visible external eye. However, they still possess several small ovular and rounded pore-sized structures where eye cells may reside. These structures, which are present on the undersides of the segments of the ovary, provide a source of nourishment for the eye tissues.
Subphylum Ethmoid requires a legume such as the crickets or grasshoppers. This phylum has a very diverse range of arthropods, with the exception of the mantis shrimp, which is an exclusively marine organism. The most commonly known representative of this subphylum is the earthworm, which has the distinction of being the only worm in the Earth that possesses both compound eyes and antennae. The most diverse subphylum in ethmoid is the plastida, with approximately 1800 species known. Some of the plastida species are well known for having anal sacs composed of a fluid that helps them move through their tunnels.