1. How does the anterior-posterior orientation of flatworms affect their movement compared to the movement of more “primitive” organisms like Hydra?

The posterior-anterior orientation of flatworms is designed in such a way that the anterior helps them in moving towards their food while the posterior ensures that these organisms walk away from irritants (Reddien, 2018). Bodies that do not have these features are unable to function like flatworms.

• Are members of phylum Platyhelminthes diploblastic or triploblastic?

Members of phylum Platyhelminthes are triploblastic.

• Are members of phylum Rotifera diploblastic or triploblastic?

Members of phylum rotifer are diploblastic.

• Are members of phylum ctenophore diploblastic or triploblastic?

Members of phylum ctenophore are triploblastic.

3. What is the benefit of a life cycle with two or more forms?

One of the advantages is that these organisms can develop from the juvenile phase easily similar to how poriferans do. Another benefit is that during their second phase, they can move in water thus ensuring that they look for various types of foods.

4. Describe the difference between diploblastic and triploblastic organisms and provide an example for each.

Diploblastic organisms generate two primary germ layers, ectoderm and endoderm during the process of gastrulation (Pukhlyakova et al., 2018). Triploblastic microorganisms, on the other hand, make three primary layers of germs; mesoderm, ectoderm and endoderm. Examples of diploblastic organisms include comb jellies, jellyfish, sea anemones and corals. Examples of triploblastic organisms include worms, molluscs, vertebrates and arthropods.

5. What is the large opening in the top of the sponge called and what is its function?

The large opening in the sponge is called osculum, and it is the location through which water is directly pushed through.

6. What are the stinging cells of Phylum Cnidaria called? What is their function?

The stinging cells in phylum cnidarian are called nematocysts (stingers). The work of stingers is to restrain toxic prey inside the cells.

7. Which lower invertebrate phylum has the greatest diversity?

The arthropod is the lower invertebrate species with the most considerable diversity.

8. Discuss why stinging cells (cnidocytes)are an effective method of capturing prey jellyfish and sea anemones to catch prey.

Cnidocytes have cells which are specialized and are found in the epidermis of every organism that is located under the cnidarians group. The cnidocytes are situated inside the epidermis part of the tentacles. The cnidocytes are essential to these organisms since they help them in catching prey.

9. Sponges and cnidarians have no gills. How do they exchange gases with the environment?

Sponges and cnidarians exchange gases through diffusion which takes place between the cells that are found in the openings of the organisms (Morandini, Custódio & Marques, 2016). Every type of cell in these organisms gets oxygen from water through the process of diffusion.

10. How does the digestive process in sponges, comb jellies and cnidarians differ?

Sponges lack a certain digestive tract but instead depend on water flow where they get oxygen and food. Comb jellies, on the other hand, utilize special enzymes in their pharynx for purposes of liquefying their food after they have swallowed it. Cnidians have a gastrovascular tract that is located in a particular part of their body that offers a location where enzymes and other cellular reactions digest food.

11. Describe the difference between polyp and Medusa.

Medusa and polyp are two body types whereby one is non-motile while the other is characteristically free swimming and is located in the marine invertebrate cnidarian.

References

Morandini, A. C., Custódio, M. R., & Marques, A. C. (2016). Phylum porifera and cnidaria. Marine and Freshwater Toxins, 287-316.

Pukhlyakova, E., Kirillova, A., Kraus, Y., & Technau, U. (2018). Cadherin switch marks germ layer formation in the diploblastic sea anemone Nematostella vectensis. bioRxiv, 488270.

Reddien, P. W. (2018). The cellular and molecular basis for planarian regeneration. Cell, 175(2), 327-345.

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