Ng Boon Yee/ Group B06/ A0099215Y
Comparison of Organisms from the Class Oligochaeta and Class Chilopoda Animal phylogeny is an interesting and rapidly changing field of study. To date, there are about 1.5 to 1.8 million species of animals that have been named and described by biologist with 15,000 to 20,000 new species named each year. However, millions more species are yet to be discovered and classified. Taxonomists have divided the animal kingdom into about 35 phyla (Solomon et al., 2011). Out of these, phylum Annelidia composed of about 15,000 species which is further divided into 3 main classes – the Polychaeta (marine worms), the Oligochaeta (earthworms and freshwater worms) and the Hirudinida (leeches). On the other hand, phylum Arthropoda is the largest animal phylum which is composed of millions of species with more than a million being described (Solomon et al., 2011). This phylum is further divided into five major subgroups – subphylum Myriapoida, subphylum Hexapoda, subphylum Chelicerata and subphylum Crustacea. In particular, the subphylum Myriapoida is further divided into two classes – the Chilopoda (centipedes) and the Diplopoda (millipedes). Lumbricus terrestris belongs to class Oligochaeta and is known as the common earthworm as it is commonly found in garden and agricultural soils of temperate regions. Similarly, Scutigera coleoptrata, also known as the house centipede from class Chilopoda, also prefers temperate climates and are often found in buildings, beneath stones or wood and in the soil. Although both species are classified under different phylum due to their phenotypic differences, biologists have assigned them into groups as the share certain ancestral characteristics with each another and also with other taxa. This essay will compare and contrast these organisms from the Class Oligochaeta (L. terrestris) and Class Chilopoda (S. coleoptrata). Although both species are easily distinguishable with an unaided eye, there are certain similarities between them. Firstly, both common earthworm and house centipede possess organ system level of body organization and are both assigned to the clade Bilateria as they both have bilateral symmetry (Solomon et al., 2011). Secondly, they are both assigned to a smaller clade, the Protostomia, due to similar pattern of early development (Solomon et al., 2011) and are also described as triplobastic as they form three germ layers during gastrulation of their blastula (Solomon et al., 2011). The three layers are ectoderm which gives rise to the tissues that form the outer covering of the body and nervous tissues, endoderm which forms the lining of the digestive tract, and mesoderm which allows the development of organs. They are both called coelomates as they possess a true coelom lined with their mesoderm which provides protection and space so that internal organs can develop and function (Solomon et al., 2011). Thirdly, both of the organisms are invertebrates and have a head and an elongated trunk with many segments (Solomon et al., 2011). The body of an adult common earthworm has more than 100 segments (Solomon et al., 2011) whereas the body of an adult house centipede has 15 segments (Ricks, 2001). Next, a complete digestive tube consisting of esophagus which is modified to form a thin-walled crop where food is stored, gizzard, intestine and anus are found in both species (Solomon et al., 2011). Lastly, both species have similar nervous system which consist of a simple brain and ventral nerve cord with ganglia (Solomon et al., 2011). Despite the similarities found between both species, they are assigned to two different groups due to certain aspects of their anatomy. To begin with, although both animals have bilateral symmetry, common earthworms have cylindrical body whereas house centipedes have dorsoventrally flattened body. Secondly, the number of segments is fixed in adult house centipedes (Ricks, 2001) but varies in common earthworms (Solomon et al.,...
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