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Table 1. Characteristics of specific taxonomic levels relating to the Astyanax jordani.
Taxon Level Taxon Name Characteristic(s)
Domain Eukarya Membrane bound organelles with a nucleus
Kingdom Animalia Eukaryote without cell wall
Phylum Chordata Hollow nerve cord that lies dorsal to notochord
Superclass Osteichthyes Bony fishes: bone skeleton
Class Actinopterygii Ray-finned fishes
Superorder Ostariophysi Weberian Apparatus
Order Characinormes Possess a small, fleshy adipose fin between dorsal fin and tail
Family Characidae Freshwater subtropical and tropical tetra fish
Genus Astyanax Broadly distributed features among the Characidae (no studies that support its monophyly)
Species jordani "Blind" Cave fish: lack of eye sight (this name sometimes refers to its close relative the Astyanax mexicanus

Figure 1. Tree indicating morphological relationships among different taxonomic groups and their sister phyla. (data taken from eol.org)

Kingdom: Animalia

-This kingdom is comprised of a major group of organisms that can sometimes be referred to as the Metazoa, along with Animalia. Characteristics of this group are: multi-cellularity, eukaryotic, ingesting heterotrophs, possess some type of skeletal support system, possess levels of cellular, tissue, organ, and system organization, possess specialized cells for particular functions, and sexual reproduction.

Phylum: Chordata*
-This phylum of organisms is characterized by four defining traits.
          1. Notochord: this is a skeletal rod that runs down the dorsal side of an animal that helps support both embryonic and adult organisms. This notochord will later develop into the vertebrae.
          2. Dorsal Nerve Cord: this is a hollow cord that is dorsal to the notochord and runs the length of the body. This same cord is found on the ventral side of the body cavity is animals that are not part of the phylum Chordata. This hollow nerve cord branches and spreads to reach different muscles of the body, connecting them to the central nervous system.
          3. Gill Structures: this structure is used as a respiratory organ in aquatic animals so that, for example, a fish can breathe in oxygen that is dissolved in water.
          4. Post-Anal Tail: this is an extension of the body past the anal opening. This is sometimes a very obvious feature in animals, for example a dog, cat, or fish; however, some do not realize that humans also fall into this category by having a tail at some point in the embryonic stage.
*(Buchsbaum, Buchsbaum, Pearse and Pearse, 1987) and (North Virginia Community College, 2002)

Superclass: Osteichthyes**
-This superclass (comprised of the Greek words Osteon=bone and ichthyes=fish) comprises what are known as the bony fishes. This means that instead of having a cartilaginous skeletal system, they will have bone. Other characteristics that define this superclass are the operculum, a flap that is found on each side of the head that covers the external side of the gills. The ability to move these flaps helps the fish to breathe without having to move and consume a lot of energy. The bony fish make up more than 95% of all fish and half of all species of invertebrates. Although some of them are herbivores, most bony fish are carnivorous. Because this superclass contains many different species of animals, relatives of the Blind Cave Fish might not seem obvious. For example the Hippocampus kelloggi, or Great Seahorse, also belongs to this superclass even though its morphology doesn't resemble the Astyanax jordani. To see other ways that these organisms are alike and different, check out the Great Seahorse HERE.
**(North Virginia Community College, 2002)

Class: Actinopterygii***
-This class, and sometimes sub-class of fishes are made up of what are called “ray-finned fishes”. This is because they possess fin rays (lepidotrichia) meaning that their fins act as webs of skin that are held together and supported by bones or spines. These boney fin rays attach directly to the basal or proximal skeletal elements. This signifies the connection between the internal skeleton and the fins. Those that are not classified under this group will have fleshy, lobed fins as opposed to boney ones.
-This class is dominant in the Chordates and is made up of nearly 95% of the 25,000 species of fish. This class is not specific to one habitat and can be found throughout marine and freshwater enviroments at all different levels of the water column. Along with a diverse habitat, this class is also known for having a range of sizes, from 8mm to 11meters to 2,300 kilograms. Another fish that belongs to this class is the Bandit Angelfish. Although lacking many of the same morphological features that the Angelfish has, it and the A. jordani both relate by possessing ray-fins. To see this intriguing and beautiful fish check out its website HERE.
***(The Virtual Fossil Museum, 2012)

Superorder: Ostariophysi
-This superorder has three defining characteristics within it to help sort out organisms: auditory specializations of the inner ear, anterior vertebrae (Weberian complex), and a gas bladder. (Tree of Life Web Project, 2005). Auditory specializations can help the fish when other sensations, like sight, are lost along with helping buoncacy in the water. (Deng, Wagner, and Popper, 2013). The Weberian Complex is an apparatus that improves audition by consisting of a double chain of ossicles that helps connect the air bladder to the inner ear. (Diogo, 2009). Gas bladders in fish are connected to the auditory section of the fish and help to maintain buoyancy and also in some specific species, play a direct role in hearing. This gas-filled sac is located in the dorsal portion of the body cavity in this superorder.

Order: Characiformes****
-This order of fish breaks down into 10 families, 237 genera, and over 1,200 species of fish. We are able to see this group of fish ranging from North America to Central and South America to Africa (some fossils found) housing in completely freshwater groups. These fish possess jaw teeth that are well developed and possess replacement teeth if needed. Along with that, pharyngeal teeth are usually present, however, some species do not have specific specialized teeth. Adipose fin and scales are almost always present, only in rare occurrences do they not show up along with commonly absent barbels. Finally, most of the fish are relatively small bodied and very colorful.
****(SBS Texas BIO 354 Lecture, 2014)

Family: Characidae*****
-This family of fish tends to inhabit tropical frishwaters of Africa and Southern and Central America. Because this group is so diverse, it is difficult to state defining characteristics. Their length can range from 3cm to 100cm, they are seen in many different colors and patterns, and tend to physically be grouped in different “common names” such as: tetras, pirahnas, etc. This shows that their diet is also non-exclusive to this family; some tend to be fierce predators while others have been seen to eat fruit that has fallen from a tree in the rainforest.
*****(Characidae, 2011)

Genus: Astyanax
-This genus of fish is a great group of species being studied in the biological field at this time and is thought to be an ideal model to investigate the importance of a geographical separation of a population resulting in groups of closely related species versus the distribution of habitats biogeographically. This is because this genus of fish inhabits a wide array of areas and levels in the water column and also because its movement is controlled by freshwater routes in a tropical area, which are surrounded by marine oceans. This genus makes up over 107 recognized species and helps comprise (with Hyphesobrycon) the largest and most diverse Characiform species. (Ornelas-García, Domínguez-Domínguez, and Doadrio, 2008).
                                        Copyright approved: Paddy Ryan
Species: jordani
-This species of fish is said to have evolved from the Astyanax mexicanus, which is a close relative that inhabits the surface of water instead of the bottom of the water column. This species of fish is known for its habitat in cave areas where it is least vulnerable for being blind and having no pigmentation. Melanin pigmentation helps to protect an animal from UV light generally, however, with this fish living in dark spaces all the time, pigmentation is not necessary for survival. (Bilandzija, Li-Ma, Parkhurst, and Jeffery, 2013).
-Both the Astyanax jordani and the Astyanax mexicanus have taste buds that are ultra sensitive and highly formed. They are found to have three types of taste buds that are elevated at different levels along with taste buds appearing in the epithelia of the lips, oral cavity, and also in the lower jaw. (Boudriot and Reutter, 2001).

Copyright Approved








Figure 2. Subtree of Group I based on Cytb gene. Subtree of Group I for the Bayesian Inference and Maximun-Parsimony methods for Astyanax  and Bramocharax based on the Ctyb gene (Ornelas-Garcia, Dominguez-Dominguez and Doadrio, 2008).

Go back home!                                                    Now that you know all about the family tree of the A. jordani check out where it lives HERE!

Want to see other organisms created by UWL students:
Check out MultipleOrganisms.net!