Platyhelminthes (flatworms)

Platyhelminthes are frequently accepted as flatworms. Some of the examples of Platyhelminthes accommodate tapeworms and flukes. These flatworms usually abide as parasites which feeds on its host or it can abide as non-parasitic animals such as the planarians (Schmidtea mediterranea). On the alternative side, Annelida are annelids which accommodate mostly earthworms, abyssal worms and leeches. These annelids are mainly detritivores which augment on sediments that accommodate microorganism. Moreover, there are additionally some alternative annelids that are hunters as they bolt their casualty with jaws. Further assay on the morphological characteristics, blazon of anatomy cavity, centralized systems and changeable apparatus allows us to accomplish added comparisons amid these two alluring phyla.

At the aboriginal glance, both flatworms and annelids allotment agnate characteristics as bilaterian animals. Animals that are bilaterally balanced beggarly that their antecedent and after ends are different. In accession to that, their after and belly surfaces are additionally different. (Refer to Fig 1 and 2) In allegory to Cnidarians and Cetenophores, Platyhelminthes and Annelids accept a college morphological and physiological organisation as they accept developed agency systems. Both Platyhelminthes and annelids acquire authentic tissues that are organised into three antibody layers, namely the endoderm, covering and mesoderm (triploblastic). The mesoderm band gives acceleration to muscles, assorted agency systems and parenchyma tissues. (Alters, 2000) Additionally, both of them accept displayed some amount of cephalisation by developing arch and tail-like structures. Furthermore, these animals are bendable bodied invertebrates and do not accept any limbs. Hence, it is their morphological attributes and structural characteristics that accord acceleration to the similarities amid Platyhelminthes and Annelida phylum group.

The appropriate mentioned aloft call the structural similarities amid the Platyhelminthes and the Annelida phylum group. However, admitting the structural similarities, there are differences empiric amid these two phylum groups. In agreement of anatomy shape, Platyhelminthes are dorsoventrally bedfast and accept unsegmented anatomy parts. Annelids, on the alternative hand, are annular and affectation metamerism. (Refer to Fig 1 and 2) Although both Platyhelminthes and Annelida are triploblastic, Platyhelminthes are acoelomates, acceptation they do not accept authentic anatomy atrium and their organs are in acquaintance with epithelium. On the contrary, Annelida are eucoelomates, they formed authentic coelom with complete lining band alleged peritoneum. (RussellHYPERLINK “#_ENREF_3” et al.HYPERLINK “#_ENREF_3”, 2011)

Most of the flatworms and annelids allotment accepted similarities in their respiratory system. Both flatworms and annelids participate in aerial barter through gas circulation in their bark layer. Generally, they respire at their integument as they do not acquire any appropriate organs for aerial exchange. Comparing their circulatory systems, the annelids accept a bankrupt circulatory arrangement which contains claret argosy abreast their bark surfaces. These claret argosy contain

blood which carries comestible and oxygen throughout the body. Claret is pump by the contractile crabbed barge which acts like a affection aural the gut. The flatworms, in contrast, do not accept any claret argosy in their anatomy and there is no specialised circulatory arrangement aural the centralized body.

Most of the flatworms acquire an abridged digestive arrangement which consists of the mouth, pharynx and an civil with one opening. Similarly, the annelids additionally acquire a aperture and pharynx. However, it has a rather complete digestive arrangement in which their civil has two openings. The two openings in the civil acquiesce for aliment movement through the aperture and allows for decay elimination through the anus. When comparing excretory arrangement in flatworms with that of annelids, assorted distinctions are discovered. The flatworms defecate their decay into the gastrovascular atrium and annihilate their decay through their mouth. On the contrary, the annelids accept a brace of excretory glands accepted as metanephridia in anniversary articulation that excretes acrid wastes products. Add on to that, solid decay articles can additionally be excreted through the bastard anus. (RussellHYPERLINK “#_ENREF_3” et al.HYPERLINK “#_ENREF_3”, 2011) Hence, both these phyla accept altered means of decay excretion.

The flatworms accept a simple afraid arrangement which consists of two simple accuracy alleged ganglia. The ganglia are a array of fretfulness which connects to the longitudinal assumption cords and run throughout on the either ancillary of the body. In addition, they accept eye spots which acquiesce them to ascertain for ablaze signatures. (Alters, 2000) On the alternative side, the afraid arrangement of annelids is rather circuitous in nature. The annelids abide of a after academician with a brace of fretfulness on either side. They additionally abide of a brace of belly assumption cords affiliated to ganglia in anniversary segment. Furthermore, they additionally accept axle fretfulness adhering to the ganglia in anniversary articulation giving the complication of the afraid arrangement in annelids.

Both flatworms and annelids accept additionally adopted agnate changeable strategies to ensure their adaptation beyond time. In their changeable mechanisms, both flatworms and annelids are able to carbon asexually or sexually. In asexual reproduction, both of them are able to carbon through clonal fragmentation. When a flatworm or an annelid is breach into fragments, anniversary of these bits will bound change and advance into a new flatworm. In beastly reproduction, both flatworms and annelids accept hermaphroditic beastly organs which acquiesce them to cantankerous fertilise via copulation. After cross-fertilisation, the bastard secretes a cushion area the fertilised eggs are deposited. Such beastly and asexual changeable strategies acquiesce these worms to bear and anticipate them from afterlife beyond the time.

The abundant assortment of attributes is a aftereffect of a continued history of evolution. Classification of animals according to their morphological appropriate provides a greater detail of account to the beastly behaviour. The similarities in the morphological anatomy and reproduction systems amid the Platyhelminthes and Annelida advance their accepted ancestry. However, anticipation abandoned from their analysis and changeable arrangement abandoned is bereft to allocate these animals. Hence, we charge to attending into alternative key characteristics that acquiesce us to differentiate amid Platyhelminthes and Annelida. One of the best important key characteristics that acquiesce us to allocate animals is genetics. Modern abiogenetic techniques acquiesce us to analyze abiogenetic sequences to acknowledge their accepted ancestry. Therefore, atomic abstracts acquired from DNA will accommodate an authentic and advantageous apparatus for the identification of the beastly phyla.

Literature Cited

Alters, S., 2000. Biology: Understanding life. Jones and Barlette Publishers.

Moore, J., 2006. An addition to the invertebrates. Cambridge University Press.

Russell, P.J., P.E. Hertz and B. McMillan, 2011. Biology: The activating science. Cengage Learning.

Table 1: shows the similarities and differences amid Platyhelminthes and Annelida







Body symmetry

Bilateral symmetry

Body structure

Soft-bodied invertebrates, does not accept limbs

Dorsoventrally flattened,



Have a arch and a tail



Acoelomates(without anatomy cavity)

Gas exchange


Diffusion through skin

Absence of claret vessels

Circulatory System

No specialised circulatory system

Digestive System

Incomplete (gut has one opening)

Excretory system

Excrete decay by mouth

Nervous System

simple assumption ganglion, accept eye spots that ascertain light


Both accept asexual and beastly reproduction

Fig 1 shows the morphological anatomy of the annelids.

Fig 2 shows the morphological anatomy of the flatworm.

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