Poriferans Are a Phylum That Is Also Known as Sponges - Essay Example

Phylum Polifera status; Paraphyletic or Monophyletic Poriferais a phylum that is also known as sponges. The sponges are multi-cellular organisms that have pored or channeled bodies. This allows water to circulate through the cells of an animal. The organisms also consists sandwiched and jelly like mesohyl in between the two layers of the cells. Polifera is a phylum of the Animalia kingdom, where as the particular phylum consists approximately five thousand species. The evolutionary branching event that created historical separation of the animals such as sponges from other metazoans led the sponges to follow their own evolutionary route of classification. The sponges were considered to be plant-animal classification until 19th Century because they were not able to move, especially during their adult life where they attach themselves to a rock. However, this paper aims to evaluate in a critical aspect about the notions that Phylum Porifera is paraphyletic rather than monophyletic. The essay achieves its purpose by providing credible sources to demonstrate the comparative knowledge of morphology and embryologoy in an effort of evaluating the suggested hypothesis. The paper demonstrates the suggestions of the notion in respect to bilaterian’s ancestors. The sponges are among the simplest animals in the Kingdom Animalia. Their feeding system is unique among other types of animals. However, the evolution of animals is believed to transform the sponges from their earlier form of multi-cellular organisms to the present day animals. As earlier mentioned, it is learnt that Poliferans had an early branching event, which resulted to their separation from other metazoans. The sponges differentiate themselves from other animals in different nature such as lacking digestive, nervous, and circulatory systems. On their side, they adapt themselves by maintaining the constant flow of water through their pored bodies in order to get oxygen and food, as well as removing waste from the body. In addition, their shape of the body is adaptive to maximal reliability of water flow though their central cavity, where it uses a hole called osculum to deposit the nutrients. Most of the sponge species feed on the food particles or bacteria in the water, where some of them host micro organisms for photosynthesizing processes to act as endosymbionts. Such associations ensure there is maximum production of oxygen and food in the water, as compared to what they consume. However, some sponges that live in environment with small or no food have become carnivores since they mainly prey on crustaceans or other living organisms. Majority of individual animals in this phylum Polifera are believed to be radically symmetrical. Furthermore, sponges are made up of layers of cells, three layers with the outer layer consisting of flattened cells that have numerous pores. This layer contains cells that are mobile and skeletal cells that result into the shape of the sponge. The innermost layer is made up of predominantly choanocytes. The choanocytes are made up of rings which surround the base of the flagella. The flagella’s main function is the facilitation of propelling of water via the pores to the body i.e. in the body central cavity. The phylum Polifera is classified into three distinct groups. This are the Hexactinellida, also referred to as the glass sponges, Calcarea, also referred to as calcareous sponges, and the Demospongia. In previous phylogenetic studies carried out by various researchers indicated that sponges are monophyletic. Recently, there has arisen several hypothesis that suggest that phylum Polifera is a paraphyletic rather than monophyletic. As it has been connoted above, phylum Polifera has been known to be monophyletic that exists within the metazoan. This is supported by various proofs ranging from the biphasic life cycle, choanocytes, filter feeding habits, aquiferous system, Pinacocytes, and choanocytes. The first phylamic activity in the investigation of higher sponge was done in the year 1992. The investigation was with molecular sequence data. This process involved the use of approximately 400 bp of 28S rDNA. In the analysis of the project, it was suggested that that sponges are Paraphyletic in Nature. Also, during the investigation, paraphyletic demosponges were found. In another different experiment carried out by Wachter and Van De Peer, in which the RNA secondary structure was used for guidance in the alignment of the 18S rDNA, approximately five hundred eukaryotic specieswere investigated. In this investigation, focus was not on the specie phylogeny. The result found illustrated that sponges were paraphyletic (Murphy, 2002). Moreover, classes that exist within this phylum Polifera can be well defined morphologically. This is due to the fact that they are characterized by triaxonic silica spicules, and the tissues forming the adult tissues are formed from syncytia, tetraxonic, monoaxonic, and polyaxonic silica spicules. Despite the fact that this Phylum Polifera is supported by molecular data, morphological analysis indicates different relation existing between the different scenarios of the monophyletic Polifera. In some of these exclusive scenarios, it has been suggested that a paraphyletic assemblage shares grade of construction, but not a common ancestry. The exclusion of sponges from monophyletic analogies is also supported by the use of minimizing the long branches attraction technique, as illustrated by Collins (1998). Some molecular studies tended to favour the monophyletic context of the sponges but Watkins and Beckenbach (1999) found the reason of having the weak statistical support. The paraphyletic position of the sponges seems to be more evidenced, especially on the basal of hexactinellid lineage in comparison to Calcarea or Demospongiae. The monophyletic nature of siliceous sponges cannot be dismissed, as there had been no clear evidence to demonstrate its paraphyletic. Or even the capabilities of determining the exact branching scenario between Demonspongiae and Hexactinellida, thereby leaving a lot of questionsfor determination. According to Kruse et al. (1998), there is weak statistical evidence claiming that Calcareous sponges are very close to Eumetazoa than other sponges, although this research study has strong evidence to demonstrate the paraphyletic assemblage of Phylum Porifera since it has more than one basal metazoan lineages. This provides a new indication of results that all ancestral organisms associated to the living metazoans were once like sponge organisms. Kumar & Rzhetsky (1996) also adds the Choanoflagellata to such scenario since it is a sister group of Metazoa. The concluded analogies of sponge paraphyly shows that even the metazoans that are non-sponge also originated from sponge ancestor by losing its adaptive systems and poriferan elements such as aquiferous and choanocyte systems. These latest analogies of molecular phylogenies have a great impact to the interference of sequential acquisition of learnt characters in early studies of animal revolution. This is because it changes the taxonomic insight of the existing history, including the taxonomic tree of evolutional routes of the particular species. For example, some analysis finds out that Homoscleromorpha was earlier grouped together with the demo-sponges but the latest studies indicate its close relations to eumetazoans, as compared to calcisponges. Such comparisons are established by the use of heir skeleton lineage that created up to three poriferan lineages with each a unique aspect. This means that the species have unique bilateral symmetry. For example, some might have the front and back end, as well as downside and upside. Others’ symmetrical scope is radially constructed like jellyfish that have only top and downside but with no front or back ends. In conclusion, the new taxonomical studies have established the new characteristics of the sponges that may change the taxonomical tree of evolutionary group of the particular animals. The sponges are said to evolve into carnivore aspect and other notions that makes them to adapt to deep sea environments since it displays a non-poriferan body lineage. The new evolutional change of the said lineage is claimed to be caused by loss of constraints that was imposed by the poriferan body structures and plan. Comparatively, the evolutional changed is focused in line with the Eumetazoa’s origin is another evidence. Dewel (2000) conducted a comparative analysis on morphology that illustrated the establishment of cnidarians grade body symmetry from poriferan grade body structure. All the analyzed evidences affirms the suggested notions from the recent studies that phylum Porifera is paraphyletic, rather than monophyletic. Moreover, the overall conclusion of the study affects the previous or historical taxonomy of ancestor groups of the Phylum Porifera. Works Cited Collins, A.G. 1998. Evaluating multiple alternative hypotheses for the origin of bilateria: an analysis of 18S rRNA molecular evidence. Proc. Nat. Acad. Sci. USA 95: 15458-15463. Dewel, R.A. 2000. Colonial origin for Eumetazoa: major morphological transitions and the origin of bilaterian complexity. J. Morph. 243: 35-74. eukaryotic kingdoms. J. Mol. Evol. 42: 183-193. Kruse, M., Leys, S.P., MuÈ ller, I.M. & MuÈ ller, W.E.G. 1998. Phylogenetic position of the Hexactinellida within the phylum Porifera based on the amino acid sequence of the protein kinase C from Rhabdocalyptus dawsoni. J. Mol. Evol. 46: 721-728. Kumar, S. & Rzhetsky, A. 1996. Evolutionary relationships of Murphy, Richard C. (2002). Coral Reefs: Cities Under The Seas. The Darwin Press, Inc. p. 51. ISBN 0-87850-138-X. Watkins, R.F. & Beckenbach, A.T. 1999. Partial sequence of a sponge mitochondrial genome reveals sequence similarity to Cnidaria in cytochrome oxidase subunit II and the large ribosomal RNA subunit. J. Mol. Evol. 48: 542-554. Read More