Question

WHAT IF? Some molecular evidence suggests that the sister group of animals is not the choanoflagellates but rather a group of parasitic protists, Mesomycetozoa. Given that these parasites lack collar cells, can this hypothesis be correct? Explain.

Short answer

The choanoflagellates have a resemblance with the sponges by the presence of collar cells. This resemblance shows that the animals and protists may have resembled choanoflagellate.

In the case of mesomycetozoa, they can be the closest relative of animals. But, mesomycetozoa lack collar cells, so it can be said that they have evolved over time and hence, do not have any resemblance with choanoflagellates.

Step-by-step solution

Choanoflagellates

Choanoflagellates are the unicellular aquatic flagellates. They have a unique morphology as they possess a single cell structure with a flagellum surrounded by small microvilli called collar cells.

Choanoflagellates are well-known for their strong resemblance to the sponge collar cells.

Mesomycetozoa (parasitic protists)

Mesomycetozoea contains aquatic microbes that belong to the animal-fungal boundary. They belong to eukaryotes and are mostly the parasites of fishes and animals.

Mesomycetozoa structure mainly comprises spherical or oval spores. They originally belonged to several groups like protozoa, fungi, or algae. However, it is said that they have both animal and fungal origins.

Relationship between animals, choanoflagellates, and mesomycetozoa in relation with collar cells

It is observed that choanoflagellates have an ancestral and structural resemblance to sponges because of their structure called collar cells. Mesomycetozoa, however, does not possess collar cells; still, they are related to animals.

The relationship between mesomycetozoa and animals suggests that they may have originated from the same ancestors. In the process of evolution, the collar cells may have evolved in a certain way that did not cause any resemblance with choanoflagellates.

Thus, this hypothesis can be correct; even if mesomycetozoa lack the collar cells, they may have become the closest relative of the animals as choanoflagellates.