Cladogram of Arthropods

Cladogram of Arthropods

A Cladogram is a diagram that is used to show the evolutionary relationship among and between groups of organisms. As such, a Cladogram is based in a phylogeny that is a field of study meant to show evolutionary relationships. As such, cladistics is a form of analysis that focuses on the features of organisms, which are considered as innovations of new features that mainly focus on the purpose of classification. To make a Cladogram, it is essential to look at the animals that are being studied and establish the characteristics, which they share in common and the ones that are unique to each group. The animal’s names are labeled on top of the Cladogram branched as well as the derived characters at the bottom of the Cladogram.

The exercise aims to apply the accumulated knowledge of evolutionary relationships of animals to act as a guide to reconstruct an accurate Cladogram of 15 animal species and also to make an analysis of musculoskeletal systems’ diversity within animals. The animals will be observed in or around Seattle. These will comprise of arthropods of all variety. The animal species are then identified by noting both common and scientific names (Edgecombe, 2010). Also, the evolution of each musculoskeletal will be mapped onto the diagram, by indicating which type of system that each of the species possesses. Also, a table will be created that will compare and contrast the anatomy, functions, as well as mechanisms of action of each of the three types of musculoskeletal systems, regardless of whether they appear in the animal species.

The arthropods are considered an influential group is accounting for about 80% of the total species. Also, they play a fundamental role in the ecological system. Moreover, the origin of arthropods has been one of the most debated subjects, especially in evolutionary biology (Edgecombe, & Legg, 2014). The arthropods are through to be closely related to annelids. However. Based on the new molecular information, the two groups are believed to be distinct from each other (Legg et al., 2012). Molecular evidence mainly favors the monophyletic arthropod origin, whereas the morphological, as well as developmental research, provides support to a polyphyletic arthropod origin. Research on extant clades can offer a precious information that can be used to trace the evolutionary history of animal species based on the living crown groups, which is considered to be somewhat inconclusive and speculative based due to lack of direct evidence for the actual ancestors.

Research on extant groups offers a key to understand the early evolution of as well as phylogenetic relationships between animal phyla. Traditionally, arthropods have been divided into four classes (Edgecombe & Legg, 2014). Arthropods are invertebrates with exoskeletons, a segmented body, coupled with paired jointed appendages.  They form the phylum Arthropoda, which comprise of insects, crustaceans, arachnids, as well as myriapods. They are mainly characterized by jointed limbs and cuticle made of chitin (Legg et al., 2012).  The body plans comprise of segments having a pair of appendages. The organisms are bilaterally symmetrical, and their bodies possess exoskeletons. The actual number of arthropods is not easy to determine. However, they are essential members of marine, freshwater, land, as well as air ecosystems.

Major Characteristics of Arthropods

There are significant characteristics of arthropods. These comprise of external and internal body segmentation that have regional specialization. The organisms also have paired articulated appendages that are mainly surrounded by chitin. Also, the cuticle forms a well-developed exoskeleton, which is generally having thick sclerotized plates. Also, the organisms have paired compound eyes that are usually present (Legg et al., 2012).  Furthermore, microorganisms grow through the process of molting. The muscles are striated and are arranged in isolated segmental bands.

The exoskeletons are non-cellular materials that are secreted by the epidermis. However, they mainly vary in the details of the structure. The exocuticle and endocuticle are jointly regarded as procuticle. Each body segment, coupled with the limb section are both hardened and protected with a hardened cuticle (Edgecombe, & Legg, 2014). A recent hypothesis indicates that biomineralization in the organisms allows them to grow larger and stronger through providing more rigid skeletons.

Although all arthropods use muscles attached to the inside of the exoskeleton, some organisms have been noted to make use of a hydraulic pressure to make them extended. Also, since the exoskeletons cannot stretch, they mainly restrict growth in the organisms. As such, the organisms replace them through molting (Legg et al., 2012). This is a process that involves shedding off the old exoskeleton after a new one has grown, which is not hardened. During the initial state of shedding off the exoskeleton, the organisms stop feeding. As a result, the endocuticle is digested and detaches.  This stage begins when the epidermis secretes a new epicuticle that is used to protect it from the enzymes.  When the stage comes to an end, the body swells through taking large amounts of water and air (Legg et al., 2012). As a result, the old cuticle splits during the process. Moreover, since the arthropods are not protected and almost immobile until a new cuticle gets hard, they are usually in gander of being trapped in the old cuticle or getting attacked by the predators.

Internal Organs

The bodies of the organisms are segmented internally. These comprise of the nervous system, muscular system, circulatory system, as well as the excretory system.  The organisms emerge from a lineage of organisms that have a membrane lined cavity, especially between the gut and the body wall (Edgecombe, & Legg, 2014). These are mainly used to protect the internal organs.  The organisms also have strong segmented limbs that mostly eliminate the need of having a hydrostatic skeleton (Edgecombe, & Legg, 2014). Muscles compress these to change the shape of the organisms and allow locomotion. However, its place is taken mainly by a cavity, which mainly runs most of the body length, and that assists in the blood flow.

Respiration and Circulation

The organisms have an open circulatory system, although most of them have open-ended arteries. On the other hand, among the crustaceans, oxygen is mainly channeled to the issues by the blood. However, in the hexapods, the air is channeled to the body tissues through the trachea. The organisms have a typical muscular tube, which mainly runs under the back (Edgecombe, & Legg, 2014). Moreover, the sections that are expanded connect the heart to the body. In the heart, some valves permit the blood to flow to the heart. However, the non-returning valves cannot prevent the blood from leaving. The organisms also have a wide variety of respiratory systems (Edgecombe, & Legg, 2014). This is attributed to the fact that they have a high surface ratio to their volume. These provide for simple diffusion of gasses through the body surface to supply oxygen. The trachea delivers oxygen directly to the cells in most organisms.

Nervous System

The organisms have paired nerve cords, which mainly run along with their bodies. Their brains are positioned in the head and are above the esophagus (Edgecombe, & Legg, 2014).  Also, the brains comprise fused ganglia and the first segments that form the head. In most arthropods, there are three pairs of ganglia, whereas the chelicerates only have two. On the other hand, the ganglia of the different head segments are positioned very close to the brain and are considered to function as part of it.

Figure 1: Cladogram of Arthropods

Figure 2: Cladogram of arthropods (Edgecombe, 2010).
References

Edgecombe, G. D. (2010). Palaeomorphology: fossils and the inference of cladistic relationships. Acta Zoologica, 91(1), 72-80. Retrieved from https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1463-6395.2009.00426.x.

Legg, D. A., Sutton, M. D., Edgecombe, G. D., & Caron, J. B. (2012). Cambrian bivalved arthropod reveals the origin of arthrodization. Proceedings of the Royal Society B: Biological Sciences, 279(1748), 4699-4704. Retrieved from https://royalsocietypublishing.org/doi/abs/10.1098/rspb.2012.1958.

Edgecombe, G. D., & Legg, D. A. (2014). Origins and early evolution of arthropods. Paleontology, 57(3), 457-468. Retrieved from https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12105

References