Comparison of Poriferans and Cnidarians

Animals are organisms belonging to kingdom Animalia and they have multiple cells and have cell tissues except for the sponges. However, unlike in plants, they lack a cell wall. Also, animals have both complex and relative movements, reproduce sexually, undergo an embryonic development consisting a blastula stage, have the ability to ingest food and they possess a nervous system. Poriferans are well known as sponges. They are primarily found in water and thus can be termed as marine organisms particularly found in sea and oceans. They are simple animals exhibiting common characteristics just like animals and only lack tissues and specialized organs. Sponges’ bodies are made up of numerous pores that allows water to circulate into their bodies enhancing wastes removal, free circulation of food and gaseous exchange. The flow of water is enhanced by the constant beating-flagella. The porous pores in their bodies have the ability to constrict and regulate the amount of water flowing into the body. Sponges have three types of cells namely pinacocytes, mesenchyme and choanocytes cells. Furthermore, sponges reproduce both sexually and asexually. For those that reproduce sexually, the male sponges release the sperms into the water and meets the egg cells of female sponges. Inside the female’s body they have very special cells called archaeocytes that transports the sperms all the way inside the female until it accomplishes the key purpose of fertilizing the female egg. On the other hand, those that reproduce asexually, form colonies where division takes place through the two processes: division of collar cells and division via the process of meiosis to form gametes that fuses to form zygotes.

Sponges have similarities as well as differences as compared to other animals. Sponges lack complex movements as most animals do and instead have limited movement mostly glued to the surface of water. In fact, some species exhibit very minimal movements. They also lack complex organs like animals and instead have skeleton-look like organs. For example, they do not have major organs like the heart, mouth, muscle and brain. In addition, they lack nervous system. Also, most of the species lack a digestive opening and instead have rampant openings on their bodies used for feeding. However, some of the sponges can change their position as well can contract just as exhibited by other species as well as absence of transport system due to efficient diffusion fostered with contact of cells with water.

Cnidarians just like poriferans predominantly live in marine or fresh water. They possess stinging cells called cnidoblast that releases cnidocysts. Their main distinguishing feature is the organized specialized cells known as cnidocytes mainly used for capturing prey. Unlike simple cells associated with porifernas, cnidarians have a bit more organized cell structures. Cnidarians belong to the group of diploblastic organisms; they have two germ layer, lower endoderm and outer ectoderm. The bodies of cnidarians are made of mesoglea that contains a substance made of one cell membrane thick and has epithelium tissue. The nervous system is quite simple as compared with other animals. Neither do they have a brain nor a nervous system. Alternatively, they possess independent-sensory nerves to smell. Additionally, they have some type of motor neurons that have the ability to contract muscles. Both these adaptations are used to detect the prey location and to determine when the enemies are attacking. As indicated before, the unique nervous system also can release cnidocyte, which is the attacking tool to the prey as it completely weakens the prey. Also, they have a mouth that can adjust to different size to capture a prey of any size. They have an incomplete digestive system formed with a gastro vascular cavity. Cnidarians lack a coelom.

Platyhelminthes are known to have three germ layers namely; ectoderm, mesoderm and endoderm, therefore, called triploblastic organisms. The mesoderm is adapted to allow for various key body functions which are beneficial to platyhelminthes. It is this unique feature that enables the muscles to be developed in the body wall aiding the body with processes. They also have advanced cells that give growth for elaborate organs enabling specialization and division of labor. It gives platyhelminthes more advantage than the cnidarians. The organs associated with these organisms are combination of myriad tissues that are specialized to perform common function. They are multi-cellular with cell tissues unlike sponges. While growing, mouth develops first during gastrulation at embryonic level of development. That explains the reason as to why these organisms are called protostomes. They are made of a bilateral symmetry that is tailored for front end cephalization. Body shape is normally elongated and slender, and it has a leaf-like or long and ribbon-like body shape. The flat body facilitates the organisms to rely on diffusion for breathing in air, absorbing nutrients and excretion of wastes. They exhibit animal characteristic of sense organs and even has a simple brain. Furthermore, this adaptation enables more efficient search for mates and food.

Platyhelminthes are also known as flatworms. Their nervous system is somewhat complex to some degree since some of them are parasites although they lack most of the organs found in other animals. Therefore, they possess some more advanced nervous system compared with the cnidarians and other phylum typically used to undertake a successful attack on other animals for food. Platyhelminthes are found in different categories of colors. Both have common features. For instance, they have the ability to alert in case of poison. Also, their nervous system is positioned in a strategic position enabling them to tell about their surrounding environment. Furthermore, the various species are endowed with different unique adaptations for survivability. Succinctly, these species comprises of trematodas distinguished with the numerous large nerves that surrounds critical parts of their bodies.

Cestoda is a simpler class of platyhelminthes but has its unique nervous system. Cestoda have scolex-type of organs that have the ability to sense and detects their prey and the enemy. Normally, the more scolex-type of sensory organs they have, the more they are advanced.

Additionally, there is the class Turbellaria, whose nerve system is centrally located at the head and has several nerves around the head. They have close resemblance to the phylum cnidarian. However, this class camouflages with the environment due to their brightly-appearance. They form the most primitive group of flatworms.

Mesoderm is one of the three key layers as the embryo develops. Development of mesoderm forms the basis of how other complex process functions takes place in both the classes and also determines how the embryo will develop. The mesoderm is the foundation where the important organs develop. When the embryo grows fully, these organs forms the important parts of the body which includes the skin tissue, muscles, reproductive and urinary system, bones and several internal body organs. Moreover, this layer forms the body cavity at the later stages of development that is beneficial to the entire body as it houses the key delicate organs of the body providing protection. Schizocoelom are a type of coelom that is formed when the mesoderm splits, while enterocoelom are formed due to pinching of mesoderm tissues normally takes place when the embryo has reached a gastrula stage of development.

Flatworms do not have a multi-functional mouth which can act as both as channel where food is taken and also a point of releasing body wastes. The excretory system comprises of connected tubules that are in the same connection with the various opening pores in the body. As such, that aids the mouth in facilitating easy excretion of wastes in the body. The flatworm has two openings. They have a mouth for the food to enter the body and an anus that releases the wastes from the body. The food is digested in the stomach where there is a gizzard that ground up food ready to be absorbed. Segmented worms have a simple excretory system. They lack re acoelomate (lack coelom), hence there is no reason for transport system. Segmented worms have various excretory organs that vary widely and have correlations with the type of diet they feed in. some have no gut and gain nutrients from symbiotic bacteria that lives inside them. The gut is a straight tube that is harnessed by vertical partition within segments and ends up with the anus. Along the gut can be located as lining that houses symbiotic bacteria on other species.

Coelom is a body cavity that is filled with fluid that normally arises from the mesoderm found in embryo as one of the layers. It is predominantly associated with multi-cellular organisms. Coelom has myriad functions but primarily serves as protection to other critical organs. Coelom provides protection for the fertilization during early process of embryonic development. Also, it is used as transport mechanism for transport of gases, nutrients, hormones and wastes to several parts of the body. Besides, coelom ensures safe storage of sperms and eggs during maturation periods and also serves as temporary storage of metabolic wastes before elimination.

Cnidarians have four key patterns in their life processes. First the matured colony female and male release eggs and sperms respectively. The two mate and the egg develop into a mature planula larva. At this level, the matured larvae can grow into a polyp but there are typical bacteria, Alteromonas, which trigger their development into a polyp. The bacteria have a substance called lipophilic fluid that serves as the food for the larvae. At this stage, food is prerequisite for process continuation otherwise without food the larvae will die. Primary polyp grows to a mature Cnidarian colony and completes the process of metamorphosis.

On the other hand, Platyhelminthes undergo key process of their life cycle. At initial stage, eggs are produced that is commonly known as shelled embryo. It is surrounded by vitelline cells that becomes the food of the egg once it hatches. Then it grows into a free-swimming larva that has massive differences with the adult. First larval parasitic stage that has not gut and depend on reserved food for survival. Free living adult platyhelminths emerges and majorly feeds predacious on the dead organisms that they come across. The adult stage is then attained and the organism has enough capability to defend and feed itself.

In Mollusca, development involves two types; direct development and indirect development. In indirect development, the larvae stage takes place while direct development there is no larval stages. In Mollusca phylum, there are three types of larval stages, trochophore larva where the larva is ciliated and has distinct features such as mouth, stomach and anus. In some classes of Mollusca, this can be the final stage of metamorphosis and others they advance to the second stage called veliger. Veliger is distinguished as the most delicate stage and the larvae is usually protected with a shell. The larvae do not take any food at this stage for some time. There is growth of more complex organs like the heart and kidney that are situated at the anterior part of the body alimentary canal is matured at this stage. The cilia developed in stage one further grows long and can be used for locomotion. The next step of metamorphosis is the glochidium larvae. The larvae here have attained a highly modified organism. It is now ready to act on fish as a parasite and look for food. For Micrura (Nemertea), the egg hatches and evolves to lecitotrophic larva where it lives for a very short period of time before going through metamorphosis to become an adult.

The term “primitive characteristics” refers to those features that the organisms previously possessed over longer period of time. Advanced characteristic are the most recent characteristics that organisms have developed in order to adapt them to the changes that have taken place in recent times. Such characteristics puts the animal exhibiting them on an advantage level as compared to other animals. For this case, annelids and anthropods have transformed their body structure to accommodate for the latest changes.

Annelids belong to the Animalia kingdom that is inclusive of segmented worms and they are both terrestrial and aquatic. They have a bilateral symmetry. They are uniquely identified with coelomates (have coelom) that is elongated and segmented in shape. They have a true digestive system with the mouth as an opening and the anus as the ending and respiration takes place within their body surface. They have numerous simple hearts within their bodies with a closed respiratory system. Most parts of the bodies are not distinct. For instance, they lack a distinct head. Besides, they have a matemaric segmentation. Both internal and external fertilization takes place in annelids. Reproduction is both asexual and sexual. Asexual reproduction is advantageous in that it has the ability to increase without the need of a partner worm that saves the energetic resources that otherwise might be needed and advantage to regenerate lost parts. Sexual reproduction encompasses mixing of genomes and production of thousands of eggs to increase the probability of fertilization.

Anthropods have jointed-appendages mostly associated with this class and absent in the class annelids. Body structures are distinct with the head, thorax, abdomen and a single heart. Another characteristic is the open circulatory system. Respiratory gaseous exchange takes place at the common point gills, trachea or book lungs unlike in the annelids where gaseous exchange takes place through the skin. Although the two classes have different features, they too have similar characteristics including, bilateral symmetry, belonging to the same kingdom, have organized organs, segmented body structures, consist of hydrostatic skeleton, undergo sexual reproduction and have a complete digestive system. All these features are modified by each variety of respective class to adapt with the changes in the competition for survivability among each group.

Works Cited

Adamo, Shelly Anne. ”Norepinephrine and Octopamine: Linking Stress and Immune Function Across Phyla.” Invertebrate Survival Journal, vol. 5, 2008, pp. 12-19.

Barnes, Richard S.K. The Invertebrates: A Synthesis. John Wiley & Sons, 2009.

Friesen, Larry J. Animal Diversity. Hawaii: Nature Journal, 2018.

Jiménez‐Alfaro, Borja, et al. ”Disentangling Vegetation Diversity from Climate–Energy and Habitat Heterogeneity for Explaining Animal Geographic Patterns.” Ecology and Evolution,

vol. 6, no. 5, 2016, pp. 1515-1526.

Zagata, Craig, et al. ”Animal Diversity.” Animal Diversity Web, n.d., http://animaldiversity.org/ Accessed 13 Feb. 2018.